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1. make install Basic File Operations ls p mv rm In List files in a directory Copy a file Rename move a file Delete remove a file Create links alternative names to a file One of the first things yov ll need to do on a Linux system is manipulate files copying renaming deleting and so forth Basic File Operations 37 Is options files coreutils bin stdin stdout file opt help version The 1s command pronounced as it is spelled ell ess lists attributes of files and directories You can list files in the current directory 1s in given directories ls dirt dir2 dir3 or individually 1s file1 file2 file3 The most important options are a and 1 By default 1s hides files whose names begin with a dot the a option displays all files The 1 option produces a long listing Yw Y Y 1 smith users 149 Oct 28 2002 my data that includes from left to right the file s permissions rw r r owner smith group users size 149 bytes last modification date Oct 28 2002 and name See File Protections on page 19 for more information on permissions Useful options a List all files including those whose names begin with a dot 1 Long listing including file attributes Add the h option human readable to print file sizes in kilobytes megabytes and gigabytes instead of bytes F Decorate certain filenames with meaningful symbols
2. Figure 3 File permission bits explained In the third form each string consists of three parts an optional scope a command and permissions Scope optional u for user g for group o for other users not in the group a for all users The default is a Command to add permissions to remove permissions to set abso lute permissions ignoring existing ones Permissions r for read w for write modify x for execute for directories this is permission to cd into the directory X for conditional execute explained later u to duplicate the user permissions g to dupli cate the group permissions o to duplicate the other users permissions s for setuid or setgid and t for the sticky bit For example ug rw would add read and write permission for the user and the group a x or just x would remove execute permis sion for everyone and u r would first remove all existing permissions and then make the file readable only by its owner You can combine these strings by separating them with commas such as ug rw a x Setuid and setgid apply to executable files programs and scripts Suppose we have an executable file F owned by user smith and the group friends If file F has setuid set user ID enabled then anyone who runs F will become user smith with all her rights and privileges for the duration of the program Likewise if F has setgid File Properties 63 set group ID enabled anyo
3. y y Baie REILLY A 7 by KESTA x h gA Lh CAO e a O j Wade Bg SRW J Adi ee AU DANIEL J BARRETT E K LINUX TIAL COMMANDS LINUX POCKET GUIDE If you re looking for a quick guide to Linux you ve found it The Linux Pocket Guide covers the most useful and important parts of day to day Linux in a i M AN concise and friendly style to get you working productively in no time The Linux Pocket Guide is both a quick reference for experienced users and a guided tour for beginners It starts with general concepts like files and directories the shell and X windows and then presents detailed overviews of the most essential commands with examples You ll learn each command s purpose usage options location on disk and even the RPM package that installed it Commands are grouped by function not just alphabetically to provide an organized learning path This book is tailored to Fedora Linux the latest spinoff of Red Hat Linux but most of the information applies to any Linux system If you need to get up to speed quickly on practical Linux use or want a short functional reference by your side the Linux Pocket Guide is for you Daniel J Barrett is co author of the popular SSH The Secure Shell and Linux Security Cookbook Visit O Reilly on the Web at www oreilly com ous g8 O REILLY i 9 780596 006280 ISBN 0 596 00628 4 Linux Pocket Guide
4. Available escape characters are listed below a Alert play a beep b Backspace c Don t print the final newline same effect as n f Form feed n Line feed newline r Carriage return t Horizontal tab v Vertical tab A backslash y Single quote Double quote nnn The character whose ASCII value is nnn in octal Screen Output 145 printf format_string arguments bash shell built in stdin stdout file opt help version The printf command is an enhanced echo it prints formatted strings on standard output It operates much like the C program ming language function printf which applies a format string to a sequence of arguments to create some specified output For example printf User s is d years old n sandy 29 User sandy is 29 years old The first argument is the format string which in our example contains two format specifications s and d The subsequent arguments sandy and 29 are substituted by printf into the format string and then printed Format specifications can get fancy with floating point numbers printf That ll be 0 2f sir n 3 That ll be 3 00 sir There are two printf commands available in Linux one built into the bash shell and one in usr bin printf The two are identical except for one format specification q supported only by the bash built in it prints escape symbols so its output can be used as shell input safely Note the diffe
5. 5 gt gt HEADER lt lt opcode QUERY status NOERROR id 50419 33 flags qr rd ra QUERY 1 ANSWER 1 AUTHORITY 3 ADDITIONAL 3 124 Linux Pocket Guide 33 QUESTION SECTION jwww redhat com IN ANY 33 ANSWER SECTION www redhat com 196 IN A 66 187 232 50 33 AUTHORITY SECTION redhat com 90535 IN NS _ ns2 redhat com redhat com 90535 IN NS _ ns3 redhat com redhat com 90535 IN NS _ ns1 redhat com 33 ADDITIONAL SECTION ns2 redhat com 143358 IN A 66 187 224 210 ns3 redhat com 143358 IN A 66 187 229 10 nsi redhat com 143358 IN A 66 187 233 210 but a full discussion of nameservers is beyond the scope of this book The final optional server parameter lets you specify a particular nameserver for the query Here s one at comcast net host www redhat com ns01 jdc01 pa comcast net Using domain server Name ns01 jdc01 pa comcast net Address 66 45 25 71 53 Aliases www redhat com has address 66 187 232 50 To see all options type host by itself Useful options a Display all available information t Choose the type of nameserver query A AXFR CNAME HINFO KEY MX NS PTR SIG SOA andso on host t MX redhat com redhat com mail is handled by 20 mx2 redhat com redhat com mail is handled by 10 mx1 redhat com If the host command doesn t do what you want try dig another powerful DNS lookup utility You might also encounter the nslookup command mostly obsolete these days but st
6. Add the v option to tar to print filenames as they are processed bzip2 options files bzip2 usr bin stdin stdout file opt help version bzip2 and bunzip2 compress and uncompress files in Burrows Wheeler format Compressed files have the suffix bz2 Sample commands bzip2 file Compress file to create file bz2 Original file is deleted bzip2 c file Produce compressed data on standard output cat file bzip2 Produce compressed data on standard output bunzip2 file bz2 Uncompress file bz2 to create file Original file bz2 is deleted bunzip2 c file bz2 Uncompress the data on standard output cat file bz2 bunzip2 Uncompress the data on standard output bzcat file bz2 Uncompress the data on standard output 84 Linux Pocket Guide bzipped tar files sample commands tar cjf myfile tar bz2 dirname Pack tar tjf myfile tar bz2 List contents tar xjf myfile tar bz2 Unpack Add the v option to tar to print filenames as they are processed zip options files zip usr bin stdin stdout file opt help version zip and unzip compress and uncompress files in Windows Zip format Compressed files have the suffix zip Unlike gzip compress and bzip2 zip does not delete the original file s zip myfile zip file1 file2 file3 Pack zip r myfile zip dirname Pack recursively unzip l myfile zip List contents unzip myfile zip Unpack uuencode options newfile infile sharutils
7. Linux Pocket Guide Action Meaning Click EQ button Display graphic equalizer Double click track in playlist Play track Right click on playlist Display playlist menu audacity files audacity not included in Fedora stdin stdout file opt help version audacity is a graphical audio file editor for making changes to WAV MP3 and Ogg files Once a file is loaded you can view its waveform cut and paste audio data apply filters and special effects to the sound echo bass boost reverse etc and more Audacity is not included with Fedora but it s a highly recom mended download from http audacity sourceforge net xcdroast options xcdroast usr bin stdin stdout file opt help version xcdroast is a CD burning program with a graphical user interface It supports only SCSI CD drives If your CD writer is an IDE drive you ll need to configure it to use the ide scsi emulation module This task is far beyond the scope of our little book but basically if your CD drives show up in the output of cdrecord scanbus you should be OK Otherwise consult the CD Writing Howto at http www tldp org HOWTO CD Writing HOWTO himl Addition ally before using xcdroast visit http www xcdroast org and read the documentation especially the FAQ because setup can be tricky Then run xcdroast Click Setup and make sure all your settings are as you want them Click Save Configuration then OK to return to
8. cat myfile def File Text Manipulation 77 xyz abc sort myfile abc def xyz Useful options f Case insensitive sorting n Sort numerically i e 9 comes before 10 instead of alphabetically 10 comes before 9 because it begins with a 1 g Another numerical sorting method with a different algorithm that among other things recognizes scientific notation 7 4e3 means 7 4 times ten to the third power or 7400 Run info sort for full technical details u Unique sort ignore duplicate lines If used with c for checking sorted files fail if any consecutive lines are identical C Don t sort just check if the input is already sorted If it is print nothing otherwise print an error message b gnore leading blanks Y Reverse the output sort from greatest to least t X Use X as the field delimiter for the k option k F1 C1 F2 C2 Choose sorting keys A sorting key is a portion of a line that s considered when sorting instead of considering the entire line An example is the fifth character of each line Normally sort would consider these lines to be in sorted order aaaaz bbbby but if your sorting key is the fifth character of each line then the lines are reversed because y comes before z The syntax means ltem Meaning Default if not supplied F1 Starting field Required C1 Starting position within with field 1 1 78 Linux Pocket Guide Item Meaning
9. usr bin stdin stdout file opt help version Before the days of email attachments and MIME binary files took some work to transmit by email You would first uuencode the files pronounced you you encode into an ASCII format that looks like this begin 644 myfile M R NSE S P lt JF 60E B 4G5N lt R F 7 S W 85N 8009V 1 F lt 6X M 6YD97 1TY 344 G1R87 gt PH 1E lt WO 6X B134TA 04 3E1 24 E end Upon receiving this data the recipient would uudecode you you decode it to restore the original data To convert a file myfile into uuencoded format creating myfile uu uuencode newfile myfile gt myfile uu File Compression and Packaging 85 The first argument new file is the file to be created at decoding time It will appear in the first line of uuencoded output begin 644 newfile M R N8F S P lt F F 60E B 4GSN lt R F 7 S W amp 5N 8009V I F lt 6X To decode this uudecoded file myfile uu creating newfile uudecode myfile uu File Comparison diff Line by line comparison of two files or directories comm Line by line comparison of two sorted files cmp Byte by byte comparison of two files md5sum Compute a checksum of the given files MD5 There are three ways to compare Linux files e Line by line diff diff3 sdiff comm best suited to text files e Byte by byte cmp often used for binary files e By comparing checksums md5sum sum cksum These programs a
10. 1 PRR Oow Useful options W Print leading zeroes as necessary to give all lines the same width seq w 8 10 08 09 10 f format_string Format the output lines with a print f like format string which must include either g the default e or f seq f g 3 KKK KD KK AQ k 148 Linux Pocket Guide s string Use the given string as a separator between the numbers By default a newline is printed i e one number per line seq s 10 1 2 3 4 5 6 7 8 9 10 clear ncurses usr bin stdin stdout file opt help version This command simply clears your display or shell window Math and Calculations xcalc Display a graphical calculator expr Evaluate simple math on the command line dc Text based calculator Need a calculator Linux provides not only a familiar graphi cal calculator but also some command line programs to compute mathematical truths for you xcalc options XFree86 tools usr X11R6 bin stdin stdout file opt help version The xcalc command displays a simple graphical calculator in an X window The default is a traditional calculator if you prefer a reverse polish notation RPN calculator supply the rpn option expr expression coreutils usr bin stdin stdout file opt help version The expr command does simple math and other expression eval uation on the command line expr 7 3 10 expr 7 3 14 Special shell chara
11. 93 Don t unmount a filesystem that s in use in fact the umount command will refuse to do so for safety reasons fsck options devices e2fsprogs sbin stdin stdout file opt help version The fsck filesystem check command validates a Linux disk parti tion and if requested repairs errors found on it fsck is run automatically when your system boots however you can run it manually if you like In general unmount a device before checking it so no other programs are operating on it at the same time umount dev hda10 fsck f dev hda10 Pass 1 Checking inodes blocks and sizes Pass 2 Checking directory structure Pass 3 Checking directory connectivity Pass 4 Checking reference counts Pass 5 Checking group summary information home 172 1281696 files 11 6 non contiguous 1405555 2562359 blocks fsck is a frontend for a set of filesystem checking programs found in sbin with names beginning fsck Only certain types of file systems are supported you can list them with the command Is sbin fsck cut d f2 Useful options A Check all disks listed in etc fstab in order N Print a description of the checking that would be done but exit without performing any checking Y Fix errors interactively prompting before each fix a Fix errors automatically only if you really know what you re doing if not you can seriously mess up a filesystem sync coreutils bin st
12. HOME My home is home sally echo HOME home smith The original value is unaffected Search path A very important variable is PATH which instructs the shell where to find programs When you type any command who 24 Linux Pocket Guide the shell has to find the program s in question It consults the value of PATH which is a sequence of directories sepa rated by colons echo PATH usr local bin bin usr bin usr X11R6 bin home smith bin and looks for the who command in each of these directories If it finds who say usr bin who it rans the command Other wise it reports bash who command not found To add directories to your shell s search path temporarily modify its PATH variable For example to append usr sbin to your shell s search path PATH PATH usr sbin echo PATH usr local bin bin usr bin usr X11R6 bin home smith bin usr sbin To make this change permanent modify the PATH variable in your startup file bash_profile as explained in Tailoring Shell Behavior on page 33 Then log out and log back in Aliases The built in command alias defines a convenient shorthand for a longer command to save typing For example alias ll Is 1 defines a new command 11 that runs 1s 1 11 total 436 Yw Y Y 1 smith 3584 Oct 11 14 59 file1 YWXY XY X 1 smith 72 Aug 6 23 04 file2 Define aliases in your bashrc file see Tailoring Shell Behav ior
13. Instant Messaging on page 142 A plus sign means yes a minus sign means no and a question mark means unknown m Display information only about yourself i e the user associated with the current terminal q Quick display of usernames only and a count of users Much like the users command but it adds a count users filename coreutils usr bin stdin stdout file opt help version The users command prints a quick listing of users who have login sessions If a user is running multiple shells she appears multiple times users barrett jones smith smith smith Like the who command users reads var log utmp by default but can read from another supplied file instead finger options user host finger usr bin stdin stdout file opt help version The finger command prints user information in a short form finger Login Name Tty Idle Login Time smith Sandy Smith 0 Sep 6 17 09 barrett Daniel Barrett pts 1 24 Sep 6 17 10 jones Jill Jones pts 2 Sep 8 20 58 or a long form finger smith Login smith Name Sandy Smith Directory home smith Shell bin bash On since Sat Sep 6 17 09 EDT on 0 Last login Mon Sep 8 21 07 EDT on pts 6 from localhost o mail Project Enhance world peace Plan Mistrust first impulses they are always right Users and Their Environment 113 The user argument can be a local username or a remote user in the form user host Remote hosts will r
14. Run editor in current window emacs nw file vim file Run EditorinanewXwindow emacs file gvim file Type text text i text ESC Save amp quit x s then x c wg Quit without saving AXC zq Respond no when asked to save buffers Save x s w Save As X Ww wfilename Undo Ari u Suspend editor not in X AZ Z Switch to edit mode N A ESC Switch to command mode M x Abort command in progress g ESC Move forward f orright arrow 1 or right arrow Move backward b or left arrow h or left arrow Move up p orup arrow k or up arrow Move down n or down arrow j or down arrow Move to next word M w File Creation and Editing 53 Table 1 Basic keystrokes in emacs and vim continued Task emacs vim Move to previous word M b b Move to beginning of line a 0 Move to end of line e Move down 1 screen y nf Move up 1 screen M v b Move to beginning of buffer M lt gg Move to end of buffer M gt G Delete next character d x Delete previous character BACKSPACE X Delete next word M d de Delete previous word M BACKSPACE db Delete current line a k k dd Delete to end of line k d Define region type this keystroke Spacebar v to mark the beginning of the region then move the cursor to the end of the desired region Cut region w d Copy region M w y Paste region y p Get help h shelp Get user manual hi shelp umask options mask bash shell built in stdin stdout file opt help
15. displays a DVI file in an X window If you prefer convert a DVI file to Postscript via the dvips command and then use GhostView gv to display it dvips o myfile ps myfile dvi gv myfile ps While displaying a file xdvi has a column of buttons down the right hand side with obvious uses such as Next to move to the next page You can hide the buttons by invoking xdvi with the expert option You can also navigate the file by keystroke Keystroke Meaning q Quit n Spacebar Enter Jump to next page Precede it with a number N to jump by N Pagedown pages p Backspace Delete Jump to previous page Precede it with a number N to jump Pageup by N pages lt Jump to first page gt Jump to last page 50 Linux Pocket Guide Keystroke Meaning AL Redisplay the page R Reread the DVI file say after you ve modified it Press mouse buttons Magnify a rectangular region under the mouse cursor xdvi has dozens of command line options for tailoring its colors geometry zoom and overall behavior File Creation and Editing emacs Text editor from Free Software Foundation vim Text editor extension of Unix vi umask Set a default mode for new files and directories soffice Office suite for editing Microsoft Word Excel and PowerPoint documents abiword Edit Microsoft Word documents gnumeric Edit Excel spreadsheets To get far with Linux you must become proficient with one of its text editors The two major o
16. example to search your current directory hierarchy for files containing the word myxomatosis find printo xargs 0 grep myxomatosis 68 Linux Pocket Guide slocate options slocate usr bin stdin stdout file opt help version The slocate secure locate command creates an index database of file locations and searches it quickly If you plan to locate many files over time in a directory hierarchy that doesn t change much slocate is a good choice For locating a single file or performing more complex processing of found files use find Fedora Linux automatically indexes the entire filesystem once a day but if you ever need to create an index yourself say storing it in tmp myindex run slocate u o tmp myindex To create an index of a given directory and all its subdirectories slocate U directory o tmp myindex Then to search for a string in the index slocate d tmp myindex string What makes slocate secure During searches it will not display files that you ordinarily would not have permission to see So if the superuser created an index of a protected directory a non superuser could search it but not see the protected files Indexing options u Create index from the root directory downward U directory Create index from directory downward 1 0 1 Turn security off 0 or on 1 The default is 1 e directories Exclude one or more directories from the index S
17. indicating their types Appends to directories to executables to symbolic links to named pipes and to sockets These are just visual indicators for you not part of the filenames i Prepend the inode numbers of the files S Prepend the size of the file in blocks useful for sorting files by their size 1s s sort n R If listing a directory list its contents recursively d If listing a directory do not list its contents just the directory itself 38 Linux Pocket Guide cp options files file dir coreutils bin stdin stdout file opt help version The cp command normally copies a file cp file file2 or copies multiple files into a directory cp filet file2 file3 file4 dir Using the a or R option you can also recursively copy directories Useful options p Copy not only the file contents but also the file s permissions timestamps and if you have sufficient permission to do so its owner and group Normally the copies will be owned by you timestamped now with permissions set by applying your umask to the original permissions a Copy a directory hierarchy recursively preserving special files permissions symbolic links and hard link relationships This combines the options R recursive copy including special files p permissions and d links i Interactive mode Ask before overwriting destination files f Force the copy If
18. much more It also has a full featured email program and Usenet news reader In the Help menu select Help Contents to get started and visit http www mozilla org for full information Some other web browsers for Linux include Firebird a stripped down Mozilla http www mozilla org products firebird Netscape based on the same engine as Mozilla http www netscape com Opera http www opera com Konquerer for KDE http www konquerer org Epiphany for GNOME http www gnome org and Galeon also based on Mozilla http galeon sourceforge net lynx options URL lynx usr bin stdin stdout file opt help version lynx is a text only web browser a rarity these days but quite useful when graphics don t matter or over slow network connections lynx http www yahoo com 136 Linux Pocket Guide All browsing is done by keyboard not mouse Many pages will not look quite right especially if they use tables or frames exten sively but usually you can find your way around a site Keystroke k G q Enter Left arrow Right arrow 8 p Spacebar b Down arrow Up arrow A SE m Meaning Get help List all keystrokes and their meanings Cancel a command in progress Quit lynx Click the current link or finish the current form field Back to previous page Forward to next page or click the current link Go to a URL you ll be prompted to enter it Save print
19. or mail the current page Scroll down Scroll up Go to the next link or form field Go to the previous link or form field Go to top of page Go to end of page Return to the main home page Search for text on the page Bookmark the current page View your bookmark list Delete a bookmark Display properties of the current page and link View HTML source type again to return to normal view lynx has over 100 command line options so the manpage is well worth exploring Web Browsing 137 Useful options dump Print the rendered page to standard output and exit Compare to source source Print the HTML source to standard output and exit Compare to the wget and curl commands emacskeys Make lynx obey keystrokes reminiscent of the emacs editor vikeys Make lynx obey keystrokes reminiscent of the vim or vi editor homepage URL Set your home page URL to be URL color Turn colored text mode on and off nocolor wget options URL wget usr bin stdin stdout file opt help version The wget command hits a URL and downloads the information to a file or standard output It s great for capturing individual pages or entire web page hierarchies to arbitrary depth For example let s capture the Yahoo home page wget http www yahoo com 23 19 51 http www yahoo com gt index html Resolving www yahoo com done Connecting to www yahoo com 216 109 118 66 80 connec
20. special characters 27 basename command 42 bash Bourne Again Shell 2 20 33 command line editing 28 printf command 146 programming with shell scripts 166 176 type command 66 70 bg command 31 jobs command and 30 bin directory 16 Booleans in shell scripts 167 170 boot directory 18 Bourne Again Shell see bash brace expansion 23 break command 174 browsing the web 136 140 bunzip2 command 84 burning CDs 99 165 bzcat command 84 bzip2 command 84 tar j command and 99 C C and C languages 178 C command killing programs 32 cal command 153 Calc program soffice 56 calculator command dc 151 calculator programs 149 152 case statement 171 cat command 43 tee command and 80 CD burning programs 99 165 cd command 14 41 home directories locating 14 cdparanoia command 164 cdrecord command 99 xcdroast command and 165 cgi bin directory 16 chattr change attributes command 64 checksums comparing 90 chfn change finger command 117 chgrp command 20 62 120 chmod command 20 62 64 chown command 20 61 chsh change shell command 118 cksum program 86 90 clear command 149 clock programs 152 cmp command 86 89 columns of text extracting from files 75 combining commands 26 comm command 86 88 command line arguments in shell scripts 177 command line editing with bash 28 commands 3 combining 26 history related 29 killing 32 109 comparing file
21. two periods in a row The former means your current direc tory and the latter means your parent directory one level above So if your current directory is one two three then refers to this directory and refers to one two You move your shell from one directory to another using the cd command cd one two three More technically this command changes your shell s current working directory to be one two three This is an absolute change since the directory begins with of course you can make relative moves as well cd d Enter subdirectory d cd mydir Go up to my parent then into directory mydir File and directory names may contain most characters you expect capital and small letters numbers periods dashes underscores and most other symbols just not it s reserved for separating directories In general however avoid using spaces asterisks parentheses and other characters that have special meaning to the shell Otherwise you ll need to quote or escape these characters all the time See Quoting on page 27 Home Directories Users personal files are often found in home for ordinary users or root for superusers Your home directory is typically home your username home smith home jones etc There are several ways to locate or refer to your home directory cd With no arguments the cd command returns you i e sets the shell s working directory to your h
22. version The umask command sets or prints your default mode for creating files and directories whether they are readable writable and or executable by yourself your group and the world See File Protections on page 19 and the chmod command in File Proper ties on page 56 for more information umask 0002 54 Linux Pocket Guide umask S U IWX IWX O IX First some technical talk A umask value is a mask i e a binary value that is combined using the binary NOT AND operation with 0666 for files and 0777 for directories to produce your default protection mode For example 0002 NOT AND 0666 yields 0664 for files and 0002 NOT AND 0777 yields mode 0775 for directories If that explanation seems from outer space here is a simple recipe Use mask 0022 to give yourself full privileges and all others read execute privileges only umask 0022 touch newfile amp amp mkdir dir ls ld newfile dir YW Y Y 1 smith smith O Nov 11 12 25 newfile drwxr xr x 2 smith smith 4096 Nov 11 12 25 dir Use mask 0002 to give yourself and your default group full privi leges and read execute to others umask 0002 touch newfile amp amp mkdir dir ls ld newfile dir YW YW Y 1 smith smith O Nov 11 12 26 newfile drwxrwxr x 2 smith smith 4096 Nov 11 12 26 dir Use mask 0077 to give yourself full privileges with nothing for anyone else umask 0077 touch newfile amp amp mkdir dir
23. 1 Long output print all differences byte by byte cmp 1 myfile yourfile 494 164 172 This means at offset 494 in decimal myfile has t octal 164 but yourfile has z octal 172 sS Silent output don t print anything just exit with an appropriate return code O if the files match 1 if they don t Or other codes if the comparison fails for some reason File Comparison 89 md5sum files check file coreutils usr bin stdin stdout file opt help version The md5sum command prints a 32 byte checksum of the given files using the MD5 algorithm see http www faqs org rfcs rfc1321 html for the technical details mdSsum myfile dd63602df1cceb57966d085524c3980f myfile Two different files are highly unlikely to have the same MD5 checksum so comparing checksums is a reasonably reliable way to detect if two files differ mdSsum myfile1 cut c1 32 gt sum mdSsum myfile2 cut c1 32 gt sum2 diff q sum1 sum2 Files sum1 and sum2 differ or if a set of files has changed using check mdSsum file1 file2 file3 gt mysum mdSsum check mysum file1 OK file2 OK file3 OK echo new data gt file2 mdSsum check mysum file1 OK file2 FAILED file3 OK md5sum WARNING 1 of 3 computed checksums did NOT match Two other programs similar to mdSsum are sum and cksum which use different algorithms to compute their checksums sum is compatible with other Unix systems
24. 62 setting ownership of 61 viewing 43 51 word count program 58 ilesystem Linux 13 20 ind command 66 68 inger command 113 117 Firebird web browser 136 floppy program 95 onts directory 16 or loops 173 command line arguments and 177 oreground bringing jobs into 32 ormatting disks 91 95 FORTRAN language 178 ree command 108 sck command 94 shutdown command and 12 tp File Transfer Protocol program 131 G g77 program 178 gaim program 142 Galeon web browser 136 gcc program 178 184 Index ghostview command 49 DVI files and 50 GIMP GNU Image Manipulation Program 161 gnat program 178 GNOME graphical environment 2 Epiphany web browser 136 Fedora Linux and 10 getting help with 8 logging out shutting down 11 running shells within 11 xclock command 152 xscreensaver program 162 gnome terminal program 11 gnumeric program 56 gnuplot program 162 Google getting help from 9 gqview image viewer 160 graphical desktop 9 graphics viewing editing 160 163 grep command 71 egrep command and 73 fgrep command and 74 manipulating RPM packages 35 ps command and 105 grip command 163 groupadd command 120 groupdel command 120 groupmod command 121 groups command 119 id Gn command and 112 gunzip command 83 gv command 49 DVI files and 50 gzip command 83 software installation and 34 tar z command and 99 H hard links 40 head command 45 help and tut
25. Daniel J Barrett O REILLY Beijing Cambridge Farnham K ln Paris Sebastopol Taipei Tokyo Linux Pocket Guide by Daniel J Barrett Copyright 2004 O Reilly Media Inc All rights reserved Printed in the United States of America Published by O Reilly Media Inc 1005 Gravenstein Highway North Sebastopol CA 95472 O Reilly Media Inc books may be purchased for educational business or sales promotional use Online editions are also available for most titles safari oreilly com For more information contact our corporate institutional sales department 800 998 9938 or corporate oreilly com Editor Mike Loukides Production Editor Colleen Gorman Cover Designer Emma Colby Interior Designer David Futato Printing History February 2004 First Edition Nutshell Handbook the Nutshell Handbook logo and the O Reilly logo are registered trademarks of O Reilly Media Inc The Pocket Guide series designations Linux Pocket Guide the image of a roper and related trade dress are trademarks of O Reilly Media Inc Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks Where those designations appear in this book and O Reilly Media Inc was aware of a trademark claim the designations have been printed in caps or initial caps While every precaution has been taken in the preparation of this book the publisher and author assume no resp
26. File Text Manipulation 75 paste numbers letters A B C paste letters numbers 1 DAWrwAnPWNnNPHUS Wm PwWwn Useful options d delimiters Use the given delimiters characters between columns the default is a tab character You can provide a single character d to be used always or a list of characters dxyz to be applied in sequence on each line the first delimiter is x then y then z then x then y sS Transpose the rows and columns of output paste s letters numbers A B C 1 2 3 4 5 tr options charset1 charset2 coreutils usr bin stdin stdout file opt help version The tr command performs some simple useful translations of one set of characters into another For example to change all vowels into asterisks cat myfile This is a very wonderful file cat myfile tr aeiouAEIOU Th s s v ry w nd rf 1 f 1 or to delete all vowels cat myfile tr d aeiouAEIOU Ths s vry wndrfl fl or to capitalize everything in the file cat myfile tr a z A Z THIS IS A VERY WONDERFUL FILE 76 Linux Pocket Guide tr translates the first character in charset into the first character in charset2 the second into the second the third into the third etc If the length of charset1 is N only the first N characters in charset2 are used If charsetd is longer than charset2 see the t option Character sets can have the following forms Form Meaning ABCD The
27. Jobs Graphics and Screensavers Audio and Video Programming with Shell Scripts Whitespace and Linebreaks Variables Input and Output Booleans and Return Codes Conditionals Loops Break and Continue 118 119 121 124 128 132 136 140 142 144 149 152 155 160 163 166 166 166 167 167 170 172 174 Contents vii Creating and Running Shell Scripts Command Line Arguments Exiting with a Return Code Beyond Shell Scripting Final Words Acknowledgments 176 177 178 178 179 179 viii Contents Linux Pocket Guide Welcome to Linux If you re a new user this book can serve as a quick introduction to Linux in general and Fedora Linux specifically as well as a guide to common and practi cal commands If you have Linux experience feel free to skip the introductory material What s in This Book This book is a short guide not a comprehensive reference We cover important useful aspects of Linux so you can work productively We do not however present every single com mand and every last option our apologies if your favorite was omitted nor delve into detail about operating system internals Short sweet and essential that s our motto We focus on commands those pesky little words you type on a command line to tell a Linux system what to do like 1s list files grep search for text in a file xmms play audio files and df measure free disk space We touch briefly on gr
28. a small but powerful programming language Here s an example of plotting the curve y x2 from x 1 to 10 which will appear in an X window on your display gnuplot gnuplot gt plot 1 10 x 2 gnuplot gt quit To do the same saving the results as a Postscript file echo set terminal postscript plot 1 10 x 2 gnuplot gt output ps See http www gnuplot info for full details xscreensaver xscreensaver ust X11R6 bin stdin stdout file opt help version The xscreensaver system is a versatile screen saver with hundreds of animations available It runs in the background and you can control it in various ways After a period of inactivity By default Fedora s graphical user interfaces KDE or GNOME run xscreensaver automatically after five minutes of inactivity You can configure this from the main menu In KDE run the Control Center application then choose Appearance amp Themes then Screen Saver Alter natively right click your mouse on the desktop choose Con figure Desktop then choose Screen Saver In GNOME choose Preferences Screensaver from the main menu As a screen locker At any time in GNOME or KDE open the main menu and choose Lock Screen Your display will remain locked until you enter your login password 162 Linux Pocket Guide On the command line Run xscreensaver demo to preview the many animations and set things up the way you like Then run xscreensaver command to con
29. and PCPU columns top options procps usr bin stdin stdout file opt help version The top command lets you monitor the most active processes updating the display at regular intervals say every second It is a screen based program that updates the display in place interactively top 116 processes 104 sleeping 1 running 0 zombie 11 stopped CPU states 1 1 user 0 5 system 0 0 nice 4 5 idle 106 Linux Pocket Guide Mem 523812K av 502328K used 21484K free OK shrd 160436K buff Swap 530104K av OK used 530104K free 115300K cached PID USER PRI NI SIZE RSS SHARE STAT CPU MEM TIME COMMAND 26265 smith 10 O 1092 1092 840 R 4 7 0 2 0 00 top 1 root 00 540 540 472 S 0 0 0 1 0 07 init 2 root 00 0 O oO SW 0 0 0 0 0 00 kflushd While top is running you can press keys to change its behavior such as setting the update speed s hiding idle processes i or killing processes k Type h to see a complete list and q to quit Useful options nN Perform N updates then quit dN Update the display every N seconds pN pM Display only the processes with PID N M up to 20 processes c Display the command line arguments of processes b Print on standard output noninteractively without playing screen tricks top b n1 gt outfile saves a quick snapshot to a file xload XFree86 tools usr X11R6 bin stdin stdout file opt help version Run xload to see a graphical display of the s
30. connects two users logged in on the same or different hosts for one to one communication It s supplied on Linux and Unix machines and has been ported to other platforms and runs in a text window such as an xterm It splits the window horizon tally so you can see your own typing and that of your partner talk friend example com If your partner is logged in multiple times you can specify one of his ttys for the talk connection write user tty util linux usr bin stdin stdout file opt help version The write program is more primitive than talk it sends lines of text from one logged in user to another on the same Linux machine write smith Hi how are you See you later D D ends the connection write is also useful in pipelines for quick one off messages echo Howdy write smith Instant Messaging 143 mesg y n SysVinit usr bin stdin stdout file opt help version The mesg program controls whether talk and write connections can reach your terminal mesg y permits them mesg n denies them and mesg prints the current status y or n mesg has no effect on modern instant messaging programs like gaim mesg is n mesg y tty coreutils usr bin stdin stdout file opt help version The tty program prints the name of the terminal device associ ated with the current shell tty dev pts 4 Screen Output echo Print simple text on standard output pri
31. display information in a longer format Iprm options job_IDs cups usr bin stdin stdout file opt help version The lprm line printer remove command cancels one or more print jobs Use lpq to learn the ID of the desired print jobs say 61 and 78 then type lprm P printername 61 78 If you don t supply any job IDs your current print job is canceled Only the superuser can cancel other users jobs The P option specifies which print queue contains the job Spelling Operations look Look up the spelling of a word quickly aspell Interactive spelling checker spell Batch spelling checker 102 Linux Pocket Guide Linux has several spellcheckers built in If you re accus tomed to graphical spellcheckers you might find Linux s fairly primitive but they can be used in pipelines which is quite powerful look options prefix dictionary_file util linux usr bin stdin stdout file opt help version The look command prints on standard output words that begin with a given string prefix The words are located in a dictionary file default usr share dict words For instance look bigg prints bigger biggest Biggs If you supply your own dictionary file any text file with alpha betically sorted lines look will print all lines beginning with the given prefix Useful options f Ignore case t X Match the prefix only up to and including the termination character X For insta
32. example use to match an asterisk or to match a backslash Alternatively put the literal character inside square brackets like or File Text Manipulation 73 Table 3 Differences plain and extended regular expressions Plain Extended Meaning Or One or more repetitions of a regular expression Zero or one occurrence of a regular expression n n Exactly n repetitions of a regular expression n n nor more repetitions of a regular expression n m n m Between n and m inclusive repetitions of a regular expression n lt m fgrep options fixed_strings files grep bin stdin stdout file opt help version The fgrep command is just like grep but instead of accepting a regular expression it accepts a list of fixed strings separated by newlines It s the same as grep F For example to search for the strings one two and three in a file fgrep one Note we are typing newline characters two three myfile fgrep is commonly used with the lowercase f option which reads patterns from a file For example if you have a dictionary file full of strings one per line cat my_dictionary file aardvark aback abandon you can conveniently search for those strings in a set of input files fgrep f my_dictionary file fgrep also is good for searching for nonalphanumeric characters like and because they are taken literally not as metachar
33. is simple given one or more files print all lines in those files that match a particular regular expression pattern For example if a file contains these lines The quick brown fox jumped over the lazy dogs My very eager mother just served us nine pancakes Film at eleven File Text Manipulation 71 and we search for all lines containing pancake we get grep pancake myfile My very eager mother just served us nine pancakes grep can use two different types of regular expressions which it calls basic and extended They are equally powerful just different and you may prefer one over the other based on your experience with other grep implementations The basic syntax is in Table 2 and Table 3 Useful options v Print only lines that do not match the regular expression 1 Print only the names of files that contain matching lines not the lines themselves L Print only the names of files that do not contain matching lines C Print only a count of matching lines n In front of each line of matching output print its original line number b In front of each line of matching output print the byte offset of the line in the input file i Case insensitive match W Match only complete words i e words that match the entire regular expression X Match only complete lines i e lines that match the entire regular expression Overrides w A N After each matching line print the next N lines from its fil
34. local_spec remote_spec openssh clients usr bin stdin stdout file opt help version The scp secure copy command copies files and directories from one computer to another in batch For an interactive user inter face see sftp It encrypts all communication between the two machines scp myfile remote example com newfile scp r mydir remote example com scp remote example com myfile scp r remote example com mydir To specify an alternate username on the remote system use the username host syntax scp myfile smith remote example com Useful options p Duplicate all file attributes permissions timestamps when copying Y Recursively copy a directory and its contents v Produce verbose output useful for debugging sftp host username host openssh clients usr bin stdin stdout file opt help version The sftp program copies files interactively between two computers As opposed to scp which copies files in batch The user interface is much like that of ftp sftp remote example com Password sftp gt cd MyFiles sftp gt Is README filet file2 file3 sftp gt get file2 Fetching home smith MyFiles file2 to file2 sftp gt quit 130 Linux Pocket Guide If your username on the remote system is different from your local one use the username host argument sftp smith remote example com Command Meaning help View a list of available commands Is
35. message to another mailbox Delete the current message While writing a message after you exit your text editor the commands in Table 5 are available Table 5 mutt commands available while writing a message Keystroke a c b wn a nN lt Meaning Attach a file an attachment to the message Set the CC list Set the BCC list Edit the message again Edit the Reply To field Edit the subject line Send the message Copy the message to a file Postpone the message without sending it The commands in Table 6 are always available Table 6 Other mutt commands Keystroke G q Meaning See a list of all commands type SPACEBAR to scroll down q to quit Cancel the command in progress Quit 134 Linux Pocket Guide The official mutt site is http www mutt org and there s a short mutt tutorial at http www cs utk edu help mail mutt_starting php mail options recipient MailX bin stdin stdout file opt help version The mail program equivalently Mail is a quick simple email client Most people want a more powerful program for regular use but for quick messages from the command line or in scripts mail is really handy To send a quick message mail smith example com Subject my subject I m typing a message To end it I type a period by itself on a line Ce jones example com To send a quick message using a single command echo Hello wor
36. name is my friend done Programming with Shell Scripts 173 myscript Tom is my friend Jack is my friend Harry is my friend The for loop is particularly handy for processing lists of files for example all files of a certain type in the current directory for file in doc do echo file is a stinky Microsoft Word file done For an infinite loop use while with the condition true or until with the condition false while true do echo forever done until false do echo forever again done Presumably you would use break or exit to terminate these loops based on some condition Break and Continue The break command jumps out of the nearest enclosing loop Consider this simple script called myscript for name in Tom Jack Harry do echo name echo again done echo all done myscript Tom again Jack again 174 Linux Pocket Guide Harry again all done Now with a break for name in Tom Jack Harry do echo name if name Jack then break fi echo again done echo all done myscript Tom again Jack The break occurs all done The continue command forces a loop to jump to its next iteration for name in Tom Jack Harry do echo name if name Jack then continue fi echo again done echo all done myscript Tom again Jack The continue occurs Harry again all done break and continue also accept a numeric argument break
37. ownership as another given file See Working with Groups on page 119 for more information on groups Useful options dereference Follow symbolic links and operate on the files they point to R Recursively change the ownership within a directory hierarchy chmod options permissions files coreutils bin stdin stdout file opt help version The chmod change mode command sets access permissions for files and directories Not every file should be available to everyone this isn t Windows 95 y know and chmod is the tool for ensuring this Typical permissions are read write and execute and they may be limited to the file owner the file s group owner and or other users The permissions argument can take three different forms e reference file to set the same permissions as another given file e An octal number up to four digits long that specifies the file s absolute permissions in bits The leftmost digit is special described later and the second third and fourth represent the file s owner the file s group and all users See Figure 3 for an example displaying the meaning of mode 0640 One or more strings specifying absolute or relative permis sions i e relative to the file s existing permissions to be applied separated by commas 62 Linux Pocket Guide Octal 0 6 4 0 Symbolic SSE YWX YwXx wx Special User Group Other attributes u 9 o All a
38. page 29 processes are part of the operating system whereas jobs are known only to the shell in which they re running A running program comprises one or more processes a job con sists of one or more programs executed as a shell command ps options procps bin stdin stdout file opt help version The ps command displays information about your running processes and optionally the processes of other users ps PID TTY TIME CMD 4706 pts 2 00 00 01 bash 15007 pts 2 00 00 00 emacs 16729 pts 2 00 00 00 ps 104 Linux Pocket Guide ps has at least 80 options we ll cover just a few useful combina tions If the options seem arbitrary or inconsistent it s because the supplied ps command GNU ps incorporates the features of several other Unix ps commands attempting to be compatible with all of them To view your processes ps ux all of user smith s processes ps U smith all occurrences of a program ps C program name processes on terminal N ps tN particular processes 1 2 and 3505 ps p1 2 3505 all processes with command lines truncated to screen width ps ef all processes with full command lines ps efww and all processes in a threaded view which indents child processes below their parents ps efH Remember you can extract information more finely from the output of ps using grep or other filter programs uptime procps usr bin stdin stdout file opt help vers
39. sequence of characters A B C D A B The range of characters from A to B x y y repetitions of the character x class The same character classes alnum digit etc accepted by grep tr also understands the escape characters a G ring bell b H backspace f L formfeed n J newline r M return t I tab and v K vertical tab accepted by printf see Screen Output on page 144 as well as the nota tion nnn to mean the character with octal value nnn tr is great for quick and simple translations but for more powerful jobs consider sed awk or perl Useful options d Delete the characters in charset from the input sS Eliminate adjacent duplicates found in charset1 from the input For example tr s aeiouAEIOU would squeeze adjacent duplicate vowels to be single vowels reeeeeeally would become really C Operate on all characters not found in charset1 t If charset1 is longer than charset2 make them the same length by truncating charset1 If t isnot present the last character of charset2 is invisibly repeated until charset2 is the same length as charset1 sort options files coreutils bin stdin stdout file opt help version The sort command prints lines of text in alphabetical order or sorted by some other rule you specify All provided files are concatenated and the result is sorted and printed
40. shells to work in a particular way edit the files bash_profile and bashrc in your home directory These files execute each time you log in bash_profile or open a shell bashrc They can set variables and aliases run programs print your horoscope or whatever you like These two files are examples of shell scripts executable files that contain shell commands We ll cover this feature in more detail in Programming with Shell Scripts on page 166 Installing Software You will probably want to add further software to your Linux system from time to time The most common forms of pack aged software for Fedora and many other Linux distros are Control D indicates end of file to any program reading from standard input In this case the program is the shell itself which terminates Installing Software 33 rpm files Red Hat Package Manager RPM files These are installed and managed with the programs rpm manually and up2date automatically tar gz files tar Z files and tar bz2 files Compressed tar files They are packaged with tar and compressed with gzip gz compress Z or bzip2 bz2 Most new software must be installed by the superuser so you ll need to run the su command or equivalent before installation For example su 1 Password KkEkkk rpm ivh mypackage rpm Ebes To locate new software check your Linux CD ROMs or visit fine sites like these http freshm
41. stdout file opt help version The cd change directory command sets your current working directory With no directory supplied cd defaults to your home directory pwd bash shell built in stdin stdout file opt help version The pwd command prints the absolute path of your current working directory pwd users smith mydir Directory Operations 41 basename path coreutils bin stdin stdout file opt help version The basename command prints the final component in a file path so for the example above basename users smith mydir mydir dirname path coreutils usr bin stdin stdout file opt help version The dirname command removes the final component from a file path dirname users smith mydir users smith dirname simply manipulates a string that is a directory name It does not change your current working directory mkdir options directories coreutils bin stdin stdout file opt help version mkdir creates one or more directories mkdir d1 d2 d3 Useful options p If you supply a directory path not just a simple directory name create any necessary parent directories automatically mkdir p one two three will create one and one two if they don t already exist then one two three m mode Create the directory with the given permissions mkdir 0755 mydir By default your shell s umask controls the permissions See the chmod command in
42. that is a command like any other so it is fol lowed by individual arguments separated by whitespace So if you mistakenly forget some whitespace 5 lt 4 No space between 4 and bash missing 168 Linux Pocket Guide then test thinks the final argument is the string 4 and complains that the final bracket is missing Table 12 Some common arguments for the test command File tests d name File name is a directory f name File name is a regular file L name File name is a symbolic link r name File name exists and is readable w name File name exists and is writable x name File name exists and is executable s name File name exists and its size is nonzero fi nt f2 File f1 is newer than file f2 fi ot f2 File 2 is older than file f2 String tests s1 52 String s1 equals string s2 s1 52 String s1 does not equal string s2 Z s1 String s1 has zero length n s1 String s1 has nonzero length Numeric tests a eq b ntegers a and b are equal a ne b ntegers a and b are not equal a gt b nteger a is greater than integer b a ge b nteger a is greater than or equal to integer b a lt b nteger a is less than integer b a le b nteger a is less than or equal to integer b Combining and negating tests t1 a t1 And Both tests t1 and t2 are true t1 o t2 Or Either test t1 or t2 is true your_test Negate the test i e your_test is false your_test Parentheses are
43. the user who created a file is its owner but relationships can get more complex Additionally a predefined group of users may have per mission to access a file Groups are defined by the sys tem administrator and are covered in Working with Groups on page 119 Finally a file or directory can be opened to all users with login accounts on the system Youll also see this set of users called the world or simply other What kind of permission is granted File owners groups and the world may each have permission to read write modify and execute run particular files Permissions also extend to directories which users may read access files within the directory write create and delete files within the directory and execute enter the directory To see the ownership and permissions of a file run ls 1 filename The Filesystem 19 To see the ownership and permissions of a directory run ls ld directory name The file permissions are the 10 leftmost characters in the out put a string of r read w write x execute and other let ters For example drwxr x Here s what these letters and symbols mean Position Meaning 1 File type file d directory 1 symbolic link p named pipe c character device b block device 2 4 Read write and execute permissions for the file s owner 5 7 Read write and execute permissions for the file s group 8 10 Read write and execute perm
44. the main screen From there choose Duplicate CD or Create CD whichever you want and continue from there Depending on how your system is configured you might need to be the superuser to burn CDs Audio and Video 165 Programming with Shell Scripts Earlier when we covered the shell bash we said it had a programming language built in In fact you can write pro grams or shell scripts to accomplish tasks that a single com mand cannot Like any good programming language the shell has variables conditionals if then else loops input and output and more Entire books have been written on shell scripting so we ll be covering the bare minimum to get you started For full documentation run info bash Whitespace and Linebreaks bash shell scripts are very sensitive to whitespace and line breaks Because the keywords of this programming lan guage are actually commands evaluated by the shell you need to separate arguments with whitespace Likewise a linebreak in the middle of a command will mislead the shell into thinking the command is incomplete Follow the con ventions we present here and you should be fine Variables We described variables earlier MYVAR 6 echo MYVAR 6 All values held in variables are strings but if they are numeric the shell will treat them as numbers when appropriate NUMBER 10 expr NUMBER 5 15 When you refer to a variable s value in a shell script it
45. the shell into the actual set of filenames they match So if you type ls a the shell first expands a into the filenames that begin with COE a in your current directory as if you had typed ls aardvark adamantium apple ls never knows you used a wildcard it sees only the final list of filenames after the shell expansion Wildcard Meaning Any set of characters except a leading period Any single character set Any single character in the given set most commonly a sequence of characters like aeiouAEIOU for all vowels or a range with a dash like A Z for all capital letters set Any single character not in the given set as above set When using sets if you want to include a literal dash in the set put it first or last To include a literal closing square bracket in the set put it first To include a or literally don t put it first 22 Linux Pocket Guide Brace expansion Similar to wildcards expressions with curly braces also expand to become multiple arguments to a command The comma separated expression a b cc ddd expands to a b cc dddd Braces work with any strings unlike wildcards which are limited to filenames For example sand X Y ZZZ wich expands to echo sand X Y ZZZ wich sandXwich sandYwich sandZZZwich regardless of what files are in the current directory Tilde expansion The shell treats tildes as special characters if they appear alone or at th
46. two digit day hh is the two digit hour mm is the two digit minute and ss is the two digit second For example t 20030812150047 represents August 12 2003 at 15 00 47 chown options user_spec files coreutils bin stdin stdout file opt help version The chown change owner command sets the ownership of files and directories chown smith myfile myfile2 mydir The user_spec parameter may be any of these possibilities e A username or numeric user ID to set the owner e A username or numeric user ID optionally followed by a colon and a group name or numeric group ID to set the owner and group e A username or numeric user ID followed by a colon to set the owner and to set the group to the invoking user s login group A group name or numeric group ID preceded by a colon to set the group only e reference file to set the same owner and group as another given file Useful options dereference Follow symbolic links and operate on the files they point to R Recursively change the ownership within a directory hierarchy File Properties 61 chgrp options group_spec files coreutils bin stdin stdout file opt help version The chgrp change group command sets the group ownership of files and directories chgrp smith myfile myfile2 mydir The group_spec parameter may be any of these possibilities e A group name or numeric group ID e reference file to set the same group
47. used for grouping as in algebra Programming with Shell Scripts 169 true and false bash has built in commands true and false which simply set their exit status to 0 and 1 respectively true echo 0 false echo 1 These will be useful when we discuss conditionals and loops Conditionals The if statement chooses between alternatives each of which may have a complex test The simplest form is the if then statement if command If exit status of command is 0 then body fi For example if whoami root then echo You are the superuser fi Next is the if then else statement if command then body1 else body2 fi For example if whoami root then echo You are the superuser else echo You are an ordinary dude fi 170 Linux Pocket Guide Finally we have the form if then elif else which may have as many tests as you like if command1 then body1 elif command2 then body2 elif else bodyN fi For example if whoami root then echo You are the superuser elif USER root then echo You might be the superuser elif bribe gt 10000 then echo You can pay to be the superuser else echo You are still an ordinary dude fi The case statement evaluates a single value and branches to an appropriate piece of code echo What would you like to do read answer case answer in eat echo OK
48. 2 1 44 1e 1062130572 1059016181 1059016308 stat tf myfile myfile bffff358 fffffffF 255 ef53 2016068 875984 773571 4096 1026144 912372 Useful options 1 Follow symbolic links and report on the file they point to f Report on the filesystem containing the file not the file itself t Terse mode print information on a single line wC options files coreutils usr bin stdin stdout file opt help version The wc word count program prints a count of bytes words and lines in presumably a text file wc myfile 24 62 428 myfile This file has 24 lines 62 whitespace delimited words and 428 bytes Useful options 1 Print the line count only W Print the word count only C Print the byte character count only L Locate the longest line in each file and print its length in bytes 58 Linux Pocket Guide du options files directories coreutils usr bin stdin stdout file opt help version The du disk usage command measures the disk space occupied by files or directories By default it measures the current direc tory and all its subdirectories printing totals in blocks for each with a grand total at the bottom du 8 Notes 36 Mail 340 Files mine 40 Files bob 416 Files 216 PC 2404 However it can also measure the size of files du myfile myfile2 4 myfile 16 myfile2 Useful options b k m Measure usage in bytes b kilobytes k
49. Default if not supplied F2 Ending field Last field C2 Starting position within ending field 1 So sort k1 5 sorts based on the first field beginning at its fifth character and sort k2 8 5 means from the eighth character of the second field to the first character of the fifth field You can repeat the k option to define multiple keys which will be applied from first to last as you specify them on the command line uniq options files coreutils usr bin stdin stdout file opt help version The uniq command operates on consecutive duplicate lines of text For example if you have a file myfile cat myfile Tana Tow then unig would detect and process in whatever way you specify the two consecutive b s but not the third b uniq myfile a b c b uniq is often used after sorting a file sort myfile uniq a b G In this case only a single b remains Also you can count dupli cate lines instead of eliminating them sort myfile uniq c 1a 3 b 1c File Text Manipulation 79 Useful options C Count adjacent duplicate lines i Case insensitive operation u Print unique lines only d Print duplicate lines only s N Ignore the first N characters on each line when detecting duplicates f N Ignore the first N whitespace separated fields on each line when detecting duplicates w N Consider only the first N characters on each line when detecting duplicates If u
50. Display a graphical clock cal Print a calendar date Print or set the date and time ntpdate Set the system time using a remote timeserver Need a date How about a good time Try these programs to display and set dates and times on your system xclock options XFree86 tools usr X11R6 bin stdin stdout file opt help version The xclock command displays a simple graphical clock in an X window If you prefer a different style there are other clock programs included such as oclock round t3d 3 D bouncing balls located outside your search path in usr X11R6 lib xscreensaver t3d and the taskbar clocks displayed by GNOME and KDE Useful options analog An analog clock with hands digital brief A digital clock with full date and time add brief to show only the time update N Update the time display every N seconds 152 Linux Pocket Guide cal options month year util linux usr bin stdin stdout file opt help version The cal command prints a calendar by default the current month cal September 2003 Su Mo Tu We Th Fr Sa 123 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 To print a different calendar supply a month and four digit year cal 8 2002 If you omit the month cal 2002 the entire year is printed Useful options y Print the current year s calendar m Business week calendar Make Monday the leftmost day j Number each day by its position
51. Fedora or other Linux system you re likely to be greeted by a graphical desktop like Figure 1 which contains e A Windows like taskbar across the bottom with A red hat icon in the lower left which when clicked pops up a main menu of programs Icons to run various programs such as the Mozilla web browser Evolution email program and Print Manager for configuring printers A desktop switcher the square with four boxes in it which lets you maintain and switch between multi ple desktops A blue checkmark indicating that your system soft ware is up to date or a red exclamation point warn ing you that it isn t A clock e Other icons on the desktop such as a trash can for delet ing files a floppy disk and your home directory folder for storing personal files Unless you re logging in remotely over the network in which case you ll see a command line prompting you to type a command Fedora AFirst View 9 Figure 1 Fedora graphical desktop Fedora comes with several similar looking interfaces and the one you re viewing is either GNOME or KDE You can tell the difference by clicking the red hat icon to bring up the main menu and choosing Help The Help window that appears will clearly indicate GNOME or KDE The Role of the Shell Explore the environment of icons and menus in GNOME and KDE These graphical interfaces are for some users the primary way to compute with Li
52. File Properties on page 56 groups usernames coreutils usr bin stdin stdout file opt help version The groups command prints the Linux groups to which you belong or to which other users belong whoami smith groups smith users groups jones root jones jones users root root bin daemon sys adm disk wheel src groupadd options group shadow utils usr sbin stdin stdout file opt help version The groupadd command creates a new group In most cases you should use the f option to prevent duplicate groups from being created groupadd f friends Useful options g gid Specify your own numeric group ID instead of letting groupadd choose one f If the specified group exists already complain and exit Different systems may store the group member list in other ways 120 Linux Pocket Guide groupdel group shadow utils usr sbin stdin stdout file opt help version The groupdel command deletes an existing group groupdel friends Before doing this it s a good idea to identify all files that have their group ID set to the given group so you can deal with them later find group friends print because groupdel does not change the group ownership of any files It simply removes the group name from the system s records groupmod options group shadow utils usr sbin stdin stdout file opt help version The groupmod command modifies the given g
53. File Properties on page 56 and File Protections on page 19 rmdir options directories coreutils bin stdin stdout file opt help version The rmdir remove directory command deletes one or more empty directories you name To delete a nonempty directory and its contents use carefully rm r directory Use rm ri directory 42 Linux Pocket Guide to delete interactively or rm rf directory to annihilate without any error messages or confirmation Useful options p Ifyou supply a directory path not just a simple directory name delete not only the given directory but the specified parent directories automatically all of which must be otherwise empty So rmdir p one two three will delete not only one two three but also one two and one if they exist File Viewing cat View files in their entirety less View files one page at atime head View the first lines of a file tail View the last lines of a file nl View files with their lines numbered od View data in octal or other formats xxd View data in hexadecimal gv View Postscript or PDF files xdvi View TeX DVI files In Linux you ll encounter various types of files to view plain text Postscript binary data and more Here we ll explain how to view them Note that commands for viewing graph ics files are covered in Graphics and Screensavers on page 160 and audio files in Audio and Video on page 163 cat options files coreut
54. Games surprise usr Files pertaining to the Kerberos authentication system kerberos usr local System files developed locally either for your organization or your individual computer usr X11R6 Files pertaining to the X window system So for a category like lib libraries your Linux system might have directories lib usr lib usr local lib usr games lib and usr X11R6 ib You might have other scopes as suits the sys tem administrator my company lib my division lib and so on The Filesystem 17 There isn t a clear distinction between and usr in practice but there is a sense that is lower level and closer to the operating system So bin contains fundamental programs like 1s and cat usr bin contains a wide variety of applica tions supplied with your Linux distribution and usr local bin contains programs your system administrator chose to install These are not hard and fast rules but typical cases Directory path part 3 application The application part of a directory path is usually the name of a program After the scope and category say usr local doc a program may have its own subdirectory say usr local doc myprogram containing files it needs Operating System Directories boot Files for booting the system This is where the kernel lives typically named boot vmlinuz lost found Damaged files that were rescued by a disk recovery tool proc Describes currently runn
55. List the files in the current remote 1s or local 11s lls directory pwd Print the remote pwd or local 1pwd working directory lpwd cd dir Change your remote cd or local 1cd directory to be dir lcd dir get file1 file2 Copy remote filez to local machine optionally renamed as file2 put file1 file2 Copy local file1 to remote machine optionally renamed as file2 mget file Copy multiple remote files to the local machine using wildcards and mput file Copy multiple local files to the remote machine using wildcards and quit Exit sftp ftp options host ftp usr bin stdin stdout file opt help version The ftp File Transfer Protocol program copies files between computers but not in a secure manner your username and pass word travel over the network as plain text Use sftp instead whenever possible The same commands we listed for sftp also work for ftp However the two programs support other differing commands too Network Connections 131 Email evolution GUI email client mutt Text based mail client mail Minimal text based mail client Fedora includes a number of mail readers We ll look at three with different purposes and strengths Other Linux mailers include pine the RMAIL and vm applications built into emacs and mozilla s Mail amp News To see the progress of email messages you send and receive view the logfile var log maillog As root you can use the mailq command to
56. N continue N to control multiple layers of loops e g jump out Programming with Shell Scripts 175 of N layers of loops but this kind of scripting leads to spa ghetti code and we don t recommend it Creating and Running Shell Scripts To create a shell script simply put bash commands into a file as you would type them To run the script you have three choices Prepend bin bash and make the file executable This is the most common way to run scripts Add the line bin bash to the very top of the script file It must be the first line of the file left justified Then make the file executable chmod x myscript Optionally move it into a directory in your search path Then run it like any other command myscript If the script is in your current directory but the current directory is not in your search path you ll need to prepend so the shell finds the script myscript The current directory is generally not in your search path for security reasons Pass to bash bash will interpret its argument as the name of a script and run it bash myscript Run in current shell with The preceding methods run your script as an indepen dent entity that has no effect on your current shell If you want your script to make changes to your current Technically it runs in a separate shell a subshell or child shell that inherits the attributes of the original shell but cannot al
57. a destination file exists overwrite it unconditionally mv options source target coreutils bin stdin stdout file opt help version The mv move command can rename a file mv file1 file2 or move files and directories into a destination directory mv file1 file2 dir3 dir4 destination directory Useful options i Interactive mode Ask before overwriting destination files f Force the move If a destination file exists overwrite it unconditionally rm options files directories coreutils bin stdin stdout file opt help version The rm remove command can delete files rm filet file2 file3 Basic File Operations 39 or recursively delete directories rm r dir1 dir2 Useful options i Interactive mode Ask before deleting each file f Force the deletion ignoring any errors or warnings Y Recursively remove a directory and its contents Use with caution especially if combined with the f option In options source target coreutils bin stdin stdout file opt help version A link is a reference to another file created by the 1n command There are two kinds of links A symbolic link refers to another file by its path much like a Windows shortcut or a Macintosh alias ln s myfile softlink If you delete the original file the now dangling link will be invalid pointing to a nonexistent file path A hard link on the other hand is simply a second name for a p
58. acks it as a job When the command completes the associated job disap pears Jobs are at a higher level than Linux processes the Linux operating system knows nothing about them They are merely constructs of the shell Some important vocabulary about job control is foreground job Running in a shell occupying the shell prompt so you cannot run another command background job Running in a shell but not occupying the shell prompt so you can run another command in the same shell suspend To stop a foreground job temporarily resume To cause a suspended job to start running again jobs The built in command jobs lists the jobs running in your current shell jobs 1 Running emacs myfile amp 2 Stopped su The integer on the left is the job number and the plus sign identi fies the default job affected by the fg foreground and bg background commands amp Placed at the end of a command line the ampersand causes the given command to run as a background job emacs myfile amp 2 28090 30 Linux Pocket Guide The shell s response includes the job number 2 and the process ID of the command 28090 Z Typing Z in a shell while a job is running in the foreground will suspend that job It simply stops running but its state is remembered mybigprogram Z 1 Stopped mybigprogram Now you re ready to type bg to put the command into the back ground or fg to resume it in t
59. acters in regular expressions 74 Linux Pocket Guide cut b c f range options files coreutils usr bin stdin stdout file opt help version The cut command extracts columns of text from files A column is defined either by character offsets e g the nineteenth char acter of each line cut c19 myfile by byte offsets which are often the same as characters unless you have multibyte characters in your language cut b19 myfile or by delimited fields e g the fifth field in each line of a comma delimited file cut d f5 myfile You aren t limited to printing a single column you can provide a range 3 16 a comma separated sequence 3 4 5 6 8 16 or both 3 4 8 16 For ranges if you omit the first number 16 a 1 is assumed 1 16 if you omit the last number 5 the end of line is used Useful options d C Use character C as the input delimiter character between fields for f By default it s a tab character output delimiter C Use character C as the output delimiter character between fields for f By default it s a tab character sS Suppress don t print lines that don t contain the delimiter character paste options files coreutils usr bin stdin stdout file opt help version The paste command is the opposite of cut treat several files as vertical columns and combine them on standard output cat letters A cat numbers WNRHOADW
60. already present on your system rpm e package _names Erase delete packages from your system In this case do not include the package version number just the pack age name For example if you install the GNU Emacs package emacs 20 7 17 i386 rpm you would uninstall it with rpm e emacs not rpm e emacs 20 7 17 rpm tar gz and tar bz2 files Packaged software files with names ending tar gz and tar bz2 typically contain source code that you ll need to compile build before installation 1 List the package contents one file per line Assure your self that each file when extracted won t overwrite 36 Linux Pocket Guide something precious on your system either accidentally or maliciously 2 Ifsa tar tvzf package tar gz less For gzip files tar tvjf package tar bz2 less For bzip2 files isfied extract the files into a new directory mkdir newdir cd newdir tar xvzf lt path gt package tar gz For gzip files tar xvjf lt path gt package tar bz2 For bzip2 files 3 Look for an extracted file named INSTALL or README Read it to learn how to build the software for example cd newdir less INSTALL 4 Usually the INSTALL or README file will tell you to run a script called configure in the current directory then run make then run make install Examine the options you may pass to the configure script configure help Then install the software configure options make su Password
61. and u options dump 0O u f dev tape usr This is called a level zero dump The u option writes a note to the file etc dumpdates to say that the backup was performed 96 Linux Pocket Guide Incremental backups may have levels 1 through 9 a level i backup stores all new and changed files since the last level i 1 backup dump 1 u f dev tape usr Don t run dump on a live filesystem actively in use unmount it first when possible restore options files sbin dump stdin stdout file opt help version The restore command reads a backup created by dump It can then restore the files to disk compare them against those on disk and other operations The friendliest way to use restore is with the i flag for interactive operation which lets you browse the tape contents just like a filesystem selecting files and directories and finally restoring them restore i f dev tape restore then prompts you for commands like the ones listed below help quit cd directory ls pwd add add filename add dir delete delete filename delete dir extract Print a help message Exit the program without restoring any files Like the shell s cd command set your current working directory within the dump for working with files Like the Linux 1s command view all files in the current working directory within the dump Like the shell s pwd command print the name of your current
62. and IRC client talk Linux Unix chat program write Send messages to a terminal mesg Prohibit talk and write tty Print your terminal device name Linux provides various ways to send messages to other users on the same machine or elsewhere on the Internet These range from the ancient programs talk and write which work over Linux terminal devices ttys to more modern Instant Messaging clients like gaim gaim options gaim usr bin stdin stdout file opt help version gaim is a instant messaging client that works with many different protocols including AOL MSN Yahoo and more It is also an IRC Internet Relay Chat client It runs in an X window gaim amp 142 Linux Pocket Guide If you don t already have an account with one of these IM services you ll need to create one first for example visit http www aim com to create an AOL Instant Messenger account Once this is done simply click the Accounts button to indicate your account to gaim enter your screen name and password in the login window and you should be connected Useful options u screenname Set your default account to be screenname 1 Automatically log in when invoking gaim assuming your password is stored w message Set yourself to be away with an optional away message talk user host tty talk usr bin stdin stdout file opt help version The talk program predates modern instant messaging by a few decades it
63. and then edit and re execute them Some useful history related commands are listed below Command Meaning history Print your history history N Print the most recent V commands in your history history c Clear delete your history L Previous command IN Command number N in your history L N The command you typed N commands ago I The last parameter from the previous command great for checking that files are present before removing them ls a xm All parameters from the previous command Filename completion Press the TAB key while you are in the middle of typing a filename and the shell will automatically complete finish typing the filename for you If several filenames match what you ve typed so far the shell will beep indicating the match is ambiguous Immediately press TAB again and the shell will present the alternatives Try this cd usr bin ls un lt TAB gt lt TAB gt Job Control jobs List your jobs amp Run a job in the background Z Suspend the current foreground job suspend Suspend a shell fg Unsuspend a job bring it into the foreground bg Make a suspended job run in the background The Shell 29 All Linux shells have job control the ability to run programs in the background multitasking behind the scenes and fore ground running as the active process at your shell prompt A job is simply the shell s unit of work When you run a command interactively your current shell tr
64. anent Any program can be made your default editor as long as it accepts a filename as an argument Regardless of how you set these variables all system admin istrators should know at least basic vim and emacs com mands in case a system tool suddenly runs an editor on a critical file emacs options files emacs usr bin stdin stdout file opt help version emacs is an extremely powerful editing environment with more commands than you could possibly imagine and a complete programming language built in to define your own editing features To invoke the emacs tutorial run emacs and type h t Most emacs keystroke commands involve the control key like F or the meta key which is usually the Escape key or the Alt key emacs s own documentation notates the meta key as M as in M F 52 Linux Pocket Guide to mean hold the meta key and type F so we will too For basic keystrokes see Table 1 vim options files vim enhanced usr bin stdin stdout file opt help version vim is an enhanced version of the old standard Unix editor vi To run the vim tutorial run vimtutor vim is a mode based editor It operates in two modes insert and normal Insert mode is for entering text in the usual manner while normal mode is for running commands like delete a line or copy paste For basic keystrokes in normal mode see Table 1 Table 1 Basic keystrokes in emacs and vim Task emacs vim
65. aphical windowing environments like GNOME and KDE each of which could fill a Pocket Guide by itself We ve organized the material by function to provide a con cise learning path For example to help you view the con tents of a file we introduce all file viewing commands together cat for short text files less for longer ones od for binary files ghostview for Postscript and so on Then we explain each of these commands in turn briefly presenting its common uses and options We assume you have an account on a Linux system and know how to log in with your username and password If not speak with your system administrator or if the system is your own use the account created when you installed Linux What s Linux Linux is a popular open source computer software environ ment that competes with Microsoft Windows and the Apple Macintosh It has four major parts The kernel The low level operating system handling files disks net working and other necessities we take for granted Supplied programs Thousands of programs for file manipulation text edit ing mathematics typesetting audio video computer programming web site creation encryption CD burn ing you name it The shell A user interface for typing commands executing them and displaying the results There are various shells in existence the Bourne shell Korn shell C shell and oth ers This book focuses on bash the Bourne Again Shell which is
66. ar File Access 0644 rw r r Uid 600 smith Gid 620 users Device 30a Inode 99492 Links 1 Access Fri Aug 29 00 16 12 2003 Modify Wed Jul 23 23 09 41 2003 Change Wed Jul 23 23 11 48 2003 and includes the filename size in bytes 1264 size in blocks 8 file type Regular File permissions in octal 0644 permissions in the format of ls rw r r owner s user ID 600 owner s name smith owner s group ID 620 owner s group name users device type 30a inode number 99492 number of hard links 1 and timestamps of the file s most recent access modifi cation and status change Filesystem information looks like stat f myfile File myfile ID bffff358 ffffftff Namelen 255 Type EXT2 Blocks Total 2016068 Free 876122 Available 773709 Size 4096 Inodes Total 1026144 Free 912372 File Properties 57 and includes the filename myfile filesystem ID bffff358 ffffffff maximum length of a filename for that filesystem 255 bytes file system type EXT2 the counts of total free and available blocks in the filesystem 2016068 876122 and 773709 respectively block size for the filesystem 4096 and the counts of total and free inodes 1026144 and 912372 respectively The t option presents the same data but on a single line without headings This is handy for processing by shell scripts or other programs stat t myfile myfile 1264 8 81a4 500 500 30a 9949
67. ard output cat file gzip Produce compressed data from a pipeline gunzip file gz Uncompress file gz to create file Original file gz is deleted gunzip c file gz Uncompress the data on standard output cat file gz gunzip Uncompress the data from a pipeline zcat file z Uncompress the data on standard output gzipped tar files sample commands tar czf myfile tar gz dirname Pack directory dirname tar tzf myfile tar gz List contents tar xzf myfile tar gz Unpack Add the v option to tar to print filenames as they are processed compress options files ncompress usr bin stdin stdout file opt help version compress and uncompress compress and uncompress files in stan dard Unix compression format Lempel Ziv Compressed files have the suffix Z File Compression and Packaging 83 Sample commands compress file Compress file to create file Z Original file is deleted compress c file Produce compressed data on standard output cat file compress Produce compressed data from a pipeline uncompress file Z Uncompress file Z to create file Original file Z is deleted uncompress c file Z Uncompress the data on standard output cat file Z uncompress Uncompress the data from a pipeline zcat file z Uncompress the data on standard output Compressed tar files sample commands tar cZf myfile tar Z dirname Pack directory dirname tar tZf myfile tar Z List contents tar xZf myfile tar Z Unpack
68. aying information about 123 news Usenet 9 140 142 nice command 109 nisdomainname command 121 nlcommand 46 cat command and 44 nslookup command 125 ntpdate command 155 0 oclock program 152 octal dump od command 47 od octal dump command 47 OLDPWD variable 24 OpenOffice org package 55 Opera web browser 136 operating system directories 18 options for commands 3 output in shell scripts 167 ownership of files 19 38 62 64 P parted program 95 partitioning disks 91 95 passwd command 117 paste command 75 patch command context diff 87 PATH variable 24 25 Perl language 178 permissions file 19 38 62 64 pidof command 109 pine mail program 132 ping command 126 pipe operator 26 printenv command 114 at command and 157 printf command 146 147 script output provided by 167 printf option find command 68 printing systems in Linux 101 proc directory 17 18 processes controlling 108 110 viewing 104 108 ps command 104 109 public_html directory 16 pwd command 41 PWD variable 24 Python language 178 Q quoting on command line 27 Index 187 R rc d directory 16 resdiff program 87 read command 167 Red Hat Linux 3 Red Hat Package Manager RPM files 34 redhat config printer command 102 redirecting input output 26 regular expressions awk filter and 81 egrep command 73 find regex command 66 grep command 71 less command and 44
69. b pages html Web pages public_html Web pages typically in users home directories www Web pages Categories for display fonts Fonts surprise X11 X window system files 16 Linux Pocket Guide Categories for hardware dev Device files for interfacing with disks and other hardware mnt Mount points directories that provide access to disks misc Categories for runtime files var Files specific to this computer created and updated as the computer runs lock Lock files created by programs to say I am running the existence of a lock file may prevent another program or another instance of the same program from running or performing an action log Log files that track important system events containing error warning and informational messages mail Mailboxes for incoming mail run PID files which contain the IDs of running processes these files are often consulted to track or kill particular processes spool Files queued or in transit such as outgoing email print jobs and scheduled jobs tmp Temporary storage for programs and or people to use proc Operating system state see Operating System Directories on page 18 Directory path part 2 scope The scope of a directory path describes at a high level the pur pose of an entire directory hierarchy Some common ones are System files supplied with Linux pronounced root usr More system files supplied with Linux pronounced user usr games
70. bose output useful for debugging telnet options host port telnet usr bin stdin stdout file opt help version The telnet program logs you into a remote machine where you already have an account telnet remote example com Avoid telnet for remote logins most implementations are inse cure and send your password over the network in plain text for anyone to steal Use ssh instead which protects your password and data via encryption There are two exceptions e In a Kerberos environment using enhanced kerberized Telnet software on both the client and server side Fedora telnet can work with Kerberos See http web mit edu kerberos for more information Connecting to a remote port when you aren t sending any sensitive information at all For example to check for the presence of a web server port 80 on a remote system telnet remote example com 80 Trying 192 168 55 21 Connected to remote example com 192 168 55 21 Escape character is XXX Type some junk and press Enter lt HTML gt lt HEAD gt Yep it s a web server lt TITLE gt 400 Bad Request lt TITLE gt lt HEAD gt lt BODY gt lt H1 gt Bad Request lt H1 gt Your browser sent a request that this server could not understand lt P gt lt BODY gt lt HTML gt Connection closed by foreign host Network Connections 129 To discourage you further from using telnet we aren t even going to describe its options scp
71. cast 192 168 0 255 Mask 255 255 255 0 UP BROADCAST RUNNING MULTICAST MTU 1500 Metric 4 RX packets 1955231 errors 0 dropped 0 overruns 0 frame 0 TX packets 1314765 errors 0 dropped 0 overruns 0 carrier 0 collisions 0 txqueuelen 100 BasicHost Information 123 RX bytes 2320504831 2213 0 Mb TX bytes 152785756 145 7 Mb Interrupt 11 Base address 0x6000 This includes your MAC address 00 50 BA 48 4F BA your IP address 192 168 0 21 your netmask 255 255 255 0 and various other information To view all loaded network interfaces run ifconfig a If you re experienced with networking see the ifconfig manpage to learn more Host Location host Look up hostnames IP addresses and DNS info whois Look up the registrants of Internet domains ping Check if a remote host is reachable traceroute View the network path to a remote host When dealing with remote computers you might want to know more about them Who owns them What are the IP addresses Where on the network are they located host options name server bind utils usr bin stdin stdout file opt help version The host command looks up the hostname or IP address of a remote machine by querying DNS host www redhat com www redhat com has address 66 187 232 50 host 66 187 232 50 50 232 187 66 in addr arpa domain name pointer www redhat com It can also find out much more host a www redhat com Trying www redhat com
72. cated bin the RPM package that installed the command coreutils and six properties of the command printed in black supported or gray unsupported stdin The command reads from standard input i e your keyboard by default stdout The command writes to standard output i e your screen by default file If you supply a dash argument in place of an input file name the command reads from standard input and likewise if the dash is supplied as an output filename the command writes to standard output For example the following wc word count command line reads the files file1 and file2 then standard input then file3 wc filet file2 file3 opt If you supply the command line option it means end of options anything appearing later on the command line is not an option This is sometimes necessary to operate on a file whose name begins with a dash which otherwise would be mistakenly treated as an option For example if you have a file named foo the command wc foo will fail because foo will be treated as an invalid option wc foo works If a command does not support you can prepend the current COE 6 Linux Pocket Guide directory path to the filename so the dash is no longer the first character wc foo help The option help makes the command print a help message explaining proper usage then exit version The option version makes the command print its
73. cdrecord rsync options source destination rsync usr bin stdin stdout file opt help version The rsync command copies a set of files It can make an exact copy including file permissions and other attributes called mirroring or it can just copy the data It can run over a network or on a single machine rsync has many uses and over 50 options we ll present just a few common cases relating to backups To mirror the directory D1 and its contents into another direc tory D2 on a single machine rsync a D1 D2 In order to mirror directory D1 over the network to another host server example com where you have an account with username smith securing the connection with SSH to prevent eavesdropping rsync a e ssh D1 smith server example com Useful options 0 Copy the ownership of the files You probably need superuser privileges on the remote host g Copy the group ownership of the files You might need superuser privileges on the remote host 100 Linux Pocket Guide p Copy the file permissions t Copy the file timestamps r Copy directories recursively i e including their contents 1 Permit symbolic links to be copied not the files they point to D Permit devices to be copied Superuser only a Mirroring copy all attributes of the original files This implies all of the options Dgloprt v Verbose mode print information about what s happening during the copy Add progre
74. ch will be executed in your login environment so you can refer to environment variables like HOME and expect them to work Use only absolute paths to your commands e g usr bin who instead of who as a general rule Table 11 shows some example time specifications Table 11 Example time specifications for crontab te Every minute 45 ee 45 minutes after each hour 1 45 2 45 etc 459 Every day at 9 45 am 459 8 The eighth day of every month at 9 45 am 45 9 8 12 Every December 8 at 9 45 am 45 9 8 dec Every December 8 at 9 45 am 459 6 Every Saturday at 9 45 am 45 9 sat Every Saturday at 9 45 am 45 9 12 6 Every Saturday in December at 9 45 am 459 8 12 6 Every December 8 AND every Saturday at 9 45 am If the command produces any output upon execution cron will email it to you Scheduling Jobs 159 Graphics and Screensavers eog Display graphics files gqview Display graphics files and slideshows ksnapshot Take a screenshot screen capture gimp Edit graphics files gnuplot Create graphs and plots xscreensaver Run a screensaver For viewing or editing graphics Linux has handy tools with tons of options We won t cover these programs in much detail just enough to pique your interest Our goal is to make you aware of the programs so you can explore further on your own eog options files eog usr bin stdin stdout file opt help version The eog Eye of Gnome image vi
75. compress bzip2 Compress files in BZip format bunzip2 Uncompress BZip files zip Compress files in Windows Zip format unzip Uncompress Windows Zip files uuencode Convert file to uuencoded format uudecode Unconvert file from uuencoded format Linux can compress files into a variety of formats and uncompress them The most popular format is GNU Zip gzip whose compressed files are named with the gz suffix Other commonly found formats are classic Unix compres sion Z suffix bzip2 compression bz2 suffix and Zip files from Windows systems zip suffix A related technology involves converting binary files into tex tual formats so they can say be transmitted within an email message Nowadays this is done automatically with attach ments and MIME tools but we ll cover the older uuencode and uudecode programs which do still get used 82 Linux Pocket Guide If you come across a format we don t cover such as Macintosh hqx sit files Arc Zoo and others you can learn more at http www fags org faqs compression faq part1 section 2 html and http www 106 ibm com developerworks library lw comp html gzip options files gzip bin stdin stdout file opt help version gzip and gunzip compress and uncompress files in GNU Zip format Compressed files have the suffix gz Sample commands gzip file Compress file to create file gz Original file is deleted gzip c file Produce compressed data on stand
76. creating empty files 51 trcommand 76 traceroute command 127 Index 189 translating characters using tr command 76 true command 170 infinite loops and 174 tty program 144 tutorials for emacs 52 getting help with Linux 7 for mutt mailer 135 for vim editor 53 twm graphical environment 10 running shells within 11 type command 66 70 locating files 66 types of files reporting 59 U umask command 54 umount command 93 uname command 19 122 uncompress command 83 uniq command 79 until loops 173 infinite loops and 174 unzip command 85 up2date command 34 uptime command 19 105 Usenet news 9 140 142 USER variable 24 useradd command 115 userdel command 116 usermod command 116 users creating new accounts 115 deleting existing users 116 finger command and 113 listing logged in users 112 modifying accounts 116 printenv command and 114 printing login names 111 printing user IDs 112 superusers and 4 updating information 117 users command 113 usr share doc directory 8 uudecode command 85 uuencode command 85 uxterm program 11 V var directory 17 variables defining 23 in shell scripts 166 vfat filesystems 91 vi text editor 51 command line editing 28 less command 45 lynx vikeys command 138 video on Linux systems 163 viewing files 43 51 processes 104 108 vim text editor 51 53 lynx vikeys command 138 sed filter and 81 VISUAL environmen
77. cters awk length o lt 60 myfile sed Like awk sed is a pattern matching engine that can perform manipulations on lines of text Its syntax is closely related to that of vim and the line editor ed Here are some trivial examples Print the file with all occurrences of the string red changed to hat sed s red hat g myfile Print the file with the first 10 lines removed sed 1 10d myfile m4 m4 is a macro processing language It locates keywords within a file and substitutes values for them For example given this file cat myfile My name is NAME and I am AGE years old ifelse QUOTE yes No matter where you go there you are see what m4 does with substitutions for NAME AGE and QUOTE m4 DNAME Sandy myfile My name is Sandy and I am AGE years old File Text Manipulation 81 m4 DNAME Sandy DAGE 25 myfile My name is Sandy and I am 25 years old m4 DNAME Sandy DAGE 25 DQUOTE yes myfile My name is Sandy and I am 25 years old No matter where you go there you are perl python Perl and Python are full fledged scripting languages power ful enough to build complete robust applications File Compression and Packaging gzip Compress files with GNU Zip gunzip Uncompress GNU Zip files compress Compress files with traditional Unix compression uncompress Uncompress files with traditional Unix compression Zcat Compress uncompress file via standard input output gzip or
78. cters are quoted 140 expr length ABCDEFG 7 expr 15 gt 16 0 Math and Calculations 149 Each argument must be separated by whitespace Notice we had to quote or escape any characters that have special meaning to the shell Parentheses escaped may be used for grouping Table 10 lists operators for expr Table 10 Operators for expr Operator Numeric operation Addition Subtraction Multiplication Integer division Remainder modulo lt Less than lt Less than or equal gt Greater than gt Greater than or equal Equality I Inequality Boolean or amp Boolean and s regexp substr s p n index s chars String operation Earlier in dictionary Earlier in dictionary or equal Later in dictionary Later in dictionary or equal Equality Inequality Boolean or Boolean and Does the regular expression regexp match string s Print n characters of string s beginning at position p p 1 is the first character Return the index of the first position in string s containing a character from string chars Return 0 if not found Same behavior as the C function index For Boolean expressions the number 0 and the empty string are considered false any other value is true For Boolean results 0 is false and 1 is true expr is not very efficient For more complex needs consider using a language like Perl instead 150 Linux Pocket Guid
79. d anewer modified newer or hada status change cnewer more recently than other file has Consider files at least mindepth or at most maxdepth N levels deep in the directory tree being searched Dereference symbolic links Proceed using depth first search completely search a directory s contents recursively before operating on the directory itself Limit the search to a single filesystem i e don t cross device boundaries Consider files of size N which can be given in blocks b one byte characters c kilobytes k or two byte words w Use N for greater than N or N for less than N File has zero size and is a regular file or directory File is owned by the given username or group name File has permissions equal to mode Use mode to check that all of the given bits are set or mode to check that any of the given bits are set You can group and negate parts of the expression with the following operators expression1 a expression2 And This is the default if two expressions appear side by side so the a is optional expression1 o expression2 Or FileLocation 67 expression not expression Negate the expression expression Precedence markers just like in algebra class Evaluate what s in parentheses first You may need to escape these from the shell with expression1 expression2 Same as the comma operator in the C programmi
80. d attempts to locate the given files by searching a hardcoded list of directories It can find executables documentation and source code whereis is somewhat quirky because its list of directories might not include the ones you need 70 Linux Pocket Guide Useful options b List only executables b manpages m or source m code files s s B dirs f files Search for executables B manpages M or source M dirs f files code files S only in the given directories You must S dirs f files terminate the directory list with the f option before listing the files you seek File Text Manipulation grep Find lines in a file that match a regular expression cut Extract columns from a file paste Append columns tr Translate characters into other characters sort Sort lines of text by various criteria uniq Locate identical lines in a file tee Copy a file and print it on standard output simultaneously One of Linux s greatest strengths is text manipulation mas saging a text file or standard input into a desired form by applying transformations Any program that reads standard input and writes standard output falls into this category but here we ll present some of the most common and powerful grep options pattern files grep bin stdin stdout file opt help version The grep command is one of the most consistently useful and powerful in the Linux arsenal Its premise
81. din stdout file opt help version The sync command flushes all disk caches to disk Usually the kernel may buffer reads writes inode changes and other disk related activity in memory sync writes the changes to disk 94 Linux Pocket Guide Normally you don t need to run this command but if say youre about to do something risky that might crash your machine running sync immediately beforehand can t hurt Partitioning and Formatting Disks Disk related operations like partitioning and formatting can be complex on Linux systems Here are pointers to the pro grams you may need start with their manpages parted fdisk Partition a hard drive Any of these programs will do they simply orsfdisk have different user interfaces mkfs Format a hard disk i e create a new filesystem floppy Format a floppy disk Backups and Remote Storage mt Control a tape drive dump Write a disk partition to tape restore Restore the results of a dump tar Read and write tape archives cdrecord Burn a CD R rsync Mirror a set of files onto another device or host There are various way to back up your precious Linux files e Copy them to a tape drive e Burn them onto a CD R e Mirror them to a remote machine Your tape backup device is usually dev htO for an IDE drive or dev st0 for a SCSI drive or for an IDE drive using ide scsi emulation It s common to make a link called dev tape to the appropriate dev
82. ditor shown in Figure 2 We ll explain these three parts slightly out of order usr local share emacs L Scope Category Application Figure 2 Directory scope category and application The Filesystem 15 Directory path part 1 category A category tells you the types of files found in a directory For example if the category is bin you can be reasonably assured that the directory contains programs Common categories are listed below Categories for programs bin Programs usually binary files sbin Programs usually binary files intended to be run by the superuser root lib Libraries of code used by programs libexec Programs invoked by other programs not usually by users think library of executable programs Categories for documentation doc Documentation info Documentation files for Emacs s built in help system man Documentation files manual pages displayed by the man program the files are often compressed or sprinkled with typesetting commands for man to interpret share Program specific files such as examples and installation instructions Categories for configuration etc Configuration files for the system and other miscellaneous stuff init d Configuration files for booting Linux also rc1 d rc2 d rc d Categories for programming include Header files for programming src Source code for programs Categories for web files cgi bin Scripts programs that run on we
83. dreds of thousands of files easily How can you find a particular file when you need to The first step is to organize your files logically into direc tories in some thoughtful manner but there are several other ways to find files depending what you re looking for File Location 65 For finding any file find is a brute force program that slogs file by file through a directory hierarchy to locate a target slocate is much faster searching through a prebuilt index that you generate as needed Fedora generates the index nightly by default For finding programs the which and type commands check all directories in your shell search path type is built into the bash shell and therefore available only when running bash while which is a program normally usr bin which type is faster and can detect shell aliases In contrast whereis exam ines a known set of directories rather than your search path find directories expression findutils usr bin stdin stdout file opt help version The find command searches one or more directories and their subdirectories recursively for files matching certain criteria It is very powerful with over 50 options and unfortunately a rather unusual syntax Here are some simple examples that search the entire file system from the root directory Find a particular file named myfile find type f name myfile print Print all directory names find type d print Use
84. e B N Before each matching line print the previous N lines from its file CN Same as A N B N print N lines from the original file above and below each matching line Y Recursively search all files in a directory and its subdirectories E Use extended regular expressions See egrep F Use lists of fixed strings instead of regular expressions See fgrep 72 Linux Pocket Guide egrep options pattern files grep bin stdin stdout file opt help version The egrep command is just like grep but uses a different extended language for regular expressions It s the same as grep E Table 2 Plain and extended regular expressions for grep Regular expression Meaning Any single character Eis Match any single character in this list ssl Match any single character NOT in this list Cece Grouping Beginning of a line End ofa line lt Beginning of a word gt End of a word alnum Any alphanumeric character alpha Any alphabetic character cntrl Any control character digit Any digit graph Any graphic character lower Any lowercase letter print Any printable character punct Any punctuation mark space Any whitespace character upper Any uppercase letter xdigit Any hexadecimal digit 7 Zero or more repetitions of a regular expression c The character c literally even if c is a special regular expression character For
85. e Y Only the kernel version m Only the hardware name p Only the processor type i Only the hardware platform 0 Only the operating system name hostname options name net tools bin stdin stdout file opt help version The hostname command prints the name of your computer Depending how you have things set up this might be the fully qualified hostname hostname myhost example com 122 Linux Pocket Guide or your short hostname hostname myhost You can also set your hostname as root hostname orange However hostnames and nameservers are complicated topics well beyond the scope of this book Don t just blindly start setting hostnames Useful options i Print your host s IP address a Print your host s alias name S Print your host s short name f Print your host s fully qualified name d Print your host s DNS domain name y Print your host s NIS or YP domain name F hostfile Set your hostname by reading the name from file host file ifconfig interface net tools sbin stdin stdout file opt help version The ifconfig command displays and sets various aspects of your computer s network interface This topic is beyond the scope of the book but we ll teach you a few tricks To display information about the default network interface usually called eth0 ifconfig etho etho Link encap Ethernet HWaddr 00 50 BA 48 4F BA inet addr 192 168 0 10 B
86. e dc options files bc usr bin stdin stdout file opt help version The dc desk calculator command is a reverse polish notation RPN stack based calculator that reads expressions from stan dard input and writes results to standard output If you know how to use a Hewlett Packard RPN calculator dc is pretty easy to use once you understand its syntax But if you re used to traditional calculators dc may seem inscrutable We ll cover only some basic commands For stack and calculator operations q Quit de Print the entire stack Delete clear the entire stack p Print the topmost value on the stack P Pop remove the topmost value from the stack nk Set precision of future operations to be n decimal places default is 0 integer operations To pop the top two values from the stack perform a requested operation and push the result Addition Subtraction Multiplication Division Remainder A Exponentiation second to top value is the base top value is the exponent To pop the top value from the stack perform a requested opera tion and push the result v Square root Examples dc 45 p Print the sum of 4 and 5 9 Math and Calculations 151 23 p Raise 2 to the 3rd power and print the result 10 p Multiply the stack top by 10 and print the result 80 f Print the stack 80 9 p Pop the top two stack values and print their sum 89 Dates and Times xclock
87. e 100 Barton Hall Office Phone 212 555 1212 212 555 1234 Home Phone Useful options f name Change the full name to name h phone Change the home phone number to phone p phone Change the office phone number to phone o office Change the office location to of fice chsh options username util linux usr bin stdin stdout file opt help version The chsh change shell command sets your login shell program Invoked without a username chsh affects your account invoked with a username by root it affects that user With no options chsh will prompt you for the desired information chsh Changing shell for smith Password New shell bin bash bin tcsh The new shell must be listed in etc shells Useful options s shell Specify the new shell 1 List all permissible shells Becoming the Superuser Normal users for the most part can modify only the files they own One special user called the superuser or root has full access to the machine and can do anything on it To become the superuser log in as yourself and type su 1 Password 118 Linux Pocket Guide You will be prompted for the superuser password which we presume you know if it s your computer Your shell prompt will change to a hash mark to indicate you are the supe ruser When finished executing commands as the superuser type D or run exit to end the superuser shell and become y
88. e a number of minutes preceded by a plus sign like 10 an absolute time in hours and minutes like 16 25 or the word now to mean immediately With no options shutdown puts the system into single user mode a special maintenance mode in which only one person is logged in at the system console and all nonessential services are off To exit single user mode either perform another shutdown to halt or reboot or type D to bring up the system in normal multiuser mode Useful options Y Reboot the system h Halt the system k Kidding don t really perform a shutdown just broadcast warning messages to all users as if the system were going down C Cancel a shutdown in progress omit the time argument f On reboot skip the usual filesystem check performed by the fsck program described in Disks and Filesystems on page 91 F On reboot require the usual filesystem check 12 Linux Pocket Guide For technical information about shutdowns single user mode and various system states see the manpages for init and inittab The Filesystem To make use of any Linux system you need to be comfort able with Linux files and their layout Every Linux file is con tained in a collection called a directory Directories are like folders on Windows and Macintosh systems Directories form a hierarchy or tree one directory may contain other directories called subdirectories which may themselves con tain other fil
89. e beginning of a word Your home directory smith User smith s home directory Shell variables You can define variables and their values by assigning them MYVAR 3 To refer to a value simply place a dollar sign in front of the variable name echo MYVAR 3 Some variables are standard and commonly defined by your shell upon login Variable Meaning DISPLAY The name of your X window display HOME The name of your home directory The Shell 23 Variable Meaning LOGNAME Your login name MAIL Path to your incoming mailbox OLDPWD Your shell s previous directory PATH Your shell search path directories separated by colons PWD Your shell s current directory SHELL The path to your shell e g bin bash TERM The type of your terminal e g xterm or vt100 USER Your login name To see a shell s variables run printenv The scope of the variable i e which programs know about it is by default the shell in which it s defined To make a variable and its value available to other programs your shell invokes i e subshells use the export command export MYVAR or the shorthand export MYVAR 3 Your variable is now called an environment variable since it s available to other programs in your shell s environment To make a specific value available to a specific program just once prepend variable value to the command line echo HOME home smith HOME home sally echo My home is
90. e decimal point printf also interprets escape characters like n print a newline character and a ring the bell See the echo command for the full list yes string coreutils usr bin stdin stdout file opt help version The yes command prints the given string or y by default forever one string per line yes again again again again Though it might seem useless at first glance yes can be perfect for turning interactive commands into batch commands Want to get rid of an annoying Are you SURE you want to do that message Pipe the output of yes into the input of the command to answer all those prompts yes my_interactive_command When my_interactive_command terminates so will yes Screen Output 147 seq options specification coreutils usr bin stdin stdout file opt help version The seq command prints a sequence of integers or real numbers suitable for piping to other programs There are three kinds of specification arguments A single number an upper limit seq begins at 1 and counts up or down to the number seq 3 1 2 3 Two numbers lower and upper limit seq begins at the first number and counts as far as it can without passing the second number seq 5 2 5 4 3 2 Three numbers lower limit increment and upper limit seq begins at the first number increments by the second number and stops at or before the third number seq 1 3 2
91. e file myfile as your crontab file The superuser can add the option u username to work with other users crontab files Crontab files contain one job per line Blank lines and comment lines beginning with are ignored Each line has six fields separated by whitespace The first five fields specify the time to run the job and the last is the job command itself Minutes of the hour Integers between 0 and 59 This can be a single number 30 a sequence of numbers separated by commas 0 15 30 45 a range 20 30 a sequence of ranges 0 15 50 59 or an asterisk to mean all You can also specify every nth time with the suffix n for instance both 12 and 0 59 12 mean 0 12 24 36 48 i e every 12 minutes Hours of the day Same syntax as for minutes Days of the month Integers between 1 and 31 again you may use sequences ranges sequences of ranges or an asterisk 158 Linux Pocket Guide Months of the year Integers between 1 and 12 again you may use sequences ranges sequences of ranges or an asterisk Additionally you may use three letter abbreviations jan feb mar but not in ranges or sequences Days of the week Integers between 0 Sunday and 6 Saturday again you may use sequences ranges sequences of ranges or an asterisk Additionally you may use three letter abbreviations sun mon tue but not in ranges or sequences Command to execute Any shell command whi
92. e name u Unsubscribe from the selected newsgroup it will be removed after you quit Type s to resubscribe When you press Enter to read a newsgroup slrn displays a Group page containing the available discussions or threads in that newsgroup Table 8 shows the useful commands on this page Table 8 Useful slrn commands for managing discussion threads Keystroke Meaning q Quit and go back to the News Groups page Down Select next thread Up Select previous thread Enter Begin reading the selected thread c Mark all threads as read catch up type ESCAPE u to undo Table 9 lists some commands you can use while reading an article Table 9 Useful slrn commands for reading articles Keystroke Meaning q Quit reading and return to the Group page Spacebar Go to next page of article b Go back to previous page of article Usenet News 141 Table 9 Useful slrn commands for reading articles continued Keystroke Meaning r Reply to the author by email f Post a followup article P Post a new article o Save the article in a file n Go to next unread article p Go to previous unread article At any time you can type for the help page slrn has a tremen dous number of commands and options and can be configured via the file slrnrc We ve covered only the basics see usr share doc slrn and http www slrn org for more information Instant Messaging gaim Instant messaging
93. eat net http freshrpms net http rpmfind net http sourceforge net up2date options packages up2date usr bin stdin stdout file opt help version up2date is the easiest way to keep your Fedora system well up to date As root just run up2date and follow the prompts This provides a graphical user inter face You can also run up2date in command line mode up2date 1 to list all updated RPM packages if any available for your system To download the given packages run up2date d packages 34 Linux Pocket Guide To install the given RPM packages you have already down loaded with up2date d run up2date i packages up2date downloads RPM packages from Red Hat or Fedora related servers over the Internet so you might need to regis ter your system with them the first time you run up2date Some Linux users prefer other programs to up2date such as yum http Ninux duke edu projects yum and apt http ayo freshrpms net rpm options files rpm bin stdin stdout file opt help version If you prefer to install RPM packages by hand use rpm the same package management program that up2date runs behind the scenes rpm not only installs the software but also makes sure your system has all prerequisites For example if pack age superstuff requires package otherstuff that you haven t installed rpm will not install superstuff If your system passes the test howev
94. een pings n Print IP addresses in the output rather than hostnames traceroute options host packet_length traceroute bin stdin stdout file opt help version The traceroute command prints the network path from your local host to a remote host and the time it takes for packets to traverse the path traceroute yahoo com 1 server example com 192 168 0 20 1 397 ms 1 973 ms 2 817 ms 2 10 221 16 1 10 221 16 1 15 397 ms 15 973 ms 10 817 ms 3 gbr2 p10 cbima ip att net 12 123 40 190 11 952 ms 11 720 ms 11 705 ms 16 p6 www dcn yahoo com 216 109 118 69 24 757 ms 22 659 ms Each host in the path is sent three probes and the return times are reported If a host does not respond within five seconds traceroute prints an asterisk Also traceroute may be blocked by firewalls or unable to proceed for various reasons in which case it prints a symbol Symbol Meaning IF Fragmentation needed IH Host unreachable IN Network unreachable IP Protocol unreachable IS Source route failed IX Communication administratively prohibited IN ICMP unreachable code N The default packet size is 40 bytes but you can change this with the final optional packet_length parameter e g traceroute myhost 120 Host Location 127 Useful options n Numeric mode print IP addresses instead of hostnames w N Change the timeout from five seconds to N seconds Network Connections ssh Securely log in
95. ell to she 11 g group Change the user s initial default group to group which can either be a numeric group ID or a group name and which must already exist G group1 group2 Make the user a member only of the additional existing groups group1 group2 and so on If the user previously belonged to other groups but you don t specify them here the user will no longer belong to them L Disable the account so the user cannot log in U Unlock the account after a L operation passwd options username passwd usr bin stdin stdout file opt help version The passwd command changes a login password yours by default passwd or another user s password if run by the superuser passwd smith passwd does have options most of them related to password expi ration Use them only in the context of a well thought out security policy chfn options username utiHinux usr bin stdin stdout file opt help version The chfn change finger command updates a few pieces of personal information maintained by the system real name home telephone office telephone and office location as displayed by the finger command Invoked without a username chfn affects your account invoked with a username by root it affects that user With no options chfn will prompt you for the desired information chfn Password Name Shawn Smith Shawn E Smith Working with User Accounts 117 Offic
96. ely This output format is the default many others are available some of which can be fed directly to other tools Try them out to see what they look like Option Output format n RCS version control format as produced by rcsdiff man rcsdiff C Context diff format as used by the patch command man patch D macro preprocessor format using ifdef macro else endif u Unified format which merges the files and prepends for deletion and for addition y Side by side format use W to adjust the width of the output e Create an ed script that would change fileA into fileB if run q Don t report changes just say whether the files differ diff can also compare directories diff dir1 dir2 File Comparison 87 which compares any same named files in those directories and lists all files that appear in one directory but not the other If you want to compare entire directory hierarchies recursively use the r option diff r dir1 dir2 which produces a potentially massive report of all differences Useful options b Don t consider whitespace B Don t consider blank lines i Ignore case Y When comparing directories recurse into subdirectories diff is just one member of a family of programs that operate on file differences Some others are diff3 which compares three files at a time and sdiff which merges the differences between two files to create a third file accordin
97. eparate their paths by commas o outfile Write the index to file outfile Search options d index Indicate which index to use in our example tmp myindex i Case insensitive search r regexp Search for files matching the given regular expression FileLocation 69 which file which usr bin stdin stdout file opt help version The which command locates an executable file in your shell s search path If you ve been invoking a program by typing its name who the which command tells you where this command is located which who usr bin who You can even find the which program itself which which usr bin which If several programs in your search path have the same name say usr bin who and usr local bin who which reports only the first type options commands bash shell built in stdin stdout file opt help version The type command like which locates an executable file in your shell s search path type grep who grep is bin grep who is usr bin who However type is built into the bash shell whereas which is a program on disk type which type rm if which is usr bin which type is a shell builtin rm is aliased to bin rm i if is a shell keyword As a built in command type is faster than which however it s available only if you re running bash whereis options files util linux usr bin stdin stdout file opt help version The whereis comman
98. er rpm completely installs the software RPM filenames typically have the form name version architecture rpm For example emacs 20 7 17 i386 rpm indicates the emacs package Version 20 7 17 for i386 Intel 80386 and higher machines Be aware that rpm sometimes requires a filename argument like emacs 20 7 17 i386 rpm and other times just the package name like emacs Common commands for manipulating RPM packages are rpm q package_name Find out if package_name is installed on your system and what version Example rpm q textutils If you don t know the name of the package a chicken and egg problem list all packages and use grep to search for likely names rpm qa grep i likely name Installing Software 35 H pm ql package_name List the files included in the given installed package Try rpm ql emacs rpm qi package_name Get general information about the package H pm qlp package rpm List the contents of an RPM file not necessarily installed yet Use qip for general information about the RPM file rpm qa List all installed RPM packages Useful for piping through grep to locate a package name rpm qa grep i emacs rpm qf filename Print the package that installed a given file on your system rpm qf usr bin who sh utils 2 0 11 rpm ivh package1 rpm package2 rpm Install packages not already present on your system rpm Fvh package1 rpm package2 rpm Update packages that are
99. es byte short long For example this command od w8 usr bin who 0000000 042577 043114 000401 000001 0000010 000000 000000 000000 000000 0000020 000002 000003 000001 000000 0000030 106240 004004 000064 000000 displays the bytes in binary file usr bin who in octal eight bytes per line The column on the left contains the file offset of each row again in octal Useful options NB Display only the first B bytes of each file specified in decimal hexadecimal by prepending 0x or 0X 512 byte blocks by appending b kilobytes by appending k or megabytes by appending m Default is to display the entire file jB Begin the output at byte 8 1 of each file acceptable formats are the same as in the N option Default 0 w 8 Display B bytes per line acceptable formats are the same as in the N option Using w by itself is equivalent to w32 Default 16 s 8 Group each row of bytes into sequences of B bytes separated by whitespace acceptable formats are the same as in the N option Using s by itself is equivalent to s3 Default 2 File Viewing 47 A djo x n Display file offsets in the leftmost column in decimal d octal o hexadecimal h or not at all n Default o t alc z Display output in a character format with nonalphanumeric characters printed as escape sequences a or by name c For z see below t dljo u x SIZE z Display output in an integer format includin
100. es and subdirectories and so on into infinity The topmost directory is called the root directory and is denoted by a slash We refer to files and directories using a names and slashes syntax called a path For instance this path one two three four refers to the root directory which contains a directory called one which contains a directory two which contains a directory three which contains a final file or directory four If a path begins with the root directory it s called an abso lute path and if not it s a relative path More on this in a moment Whenever you are running a shell that shell is in some direc tory in an abstract sense More technically your shell has a current working directory and when you run commands in that shell they operate relative there s that word again to the directory More specifically if you refer to a relative file path in that shell it is relative to your current working directory For example if your shell is in the directory one two three and you run a command that refers to a file myfile then it s really In Linux all files and directories descend from the root This is unlike Windows or DOS in which different devices are accessed by drive letters The Filesystem 13 one two three myfile Likewise a relative path a b c would imply the true path one two three a b c Two special directories are denoted a single period and
101. es several scheduling tools at vari ous degrees of complexity Scheduling Jobs 155 sleep time_specification coreutils bin stdin stdout file opt help version The sleep command simply waits a set amount of time The given time specification can be an integer meaning seconds or an integer followed by the letter s also seconds m minutes h hours or d days sleep 5m Do nothing for 5 minutes sleep is useful for delaying a command for a set amount of time sleep 10 amp amp echo Ten seconds have passed 10 seconds pass Ten seconds have passed watch options command procps usr bin stdin stdout file opt help version The watch program executes a given command at regular inter vals the default is every two seconds The command is passed to the shell so be sure to quote or escape any special characters and the results are displayed in a full screen mode so you can observe the output conveniently and see what has changed For example watch n 60 date executes the date command once a minute sort of a poor man s clock Type C to exit Useful options n seconds Set the time between executions in seconds d Highlight differences in the output to emphasize what has changed from one execution to the next at options time_specification at usr bin stdin stdout file opt help version The at command runs a shell command once at a specified time at 7am next
102. esn t call exit the return code is automatically 0 if lt 2 then echo Error you must supply two arguments exit 1 else echo My name is 1 and I come from 2 fi exit 0 myscript Bob myscript error you must supply two arguments echo a Beyond Shell Scripting Shell scripts are fine for many purposes but Linux comes with much more powerful scripting languages as well as compiled programming languages Here are a few Language Program To get started Perl perl man perl http www perl com Python python man python http www python org C C gcc man gcc http www gnu org software gcc Java javaca http java sun com FORTRAN g77 man g77 http www gnu org software fortran fortran html 178 Linux Pocket Guide Language Program To get started Ada gnat info gnat http www gnu org software gnat gnat html a Not included in Fedora nor many other Linux distros Final Words Although we ve covered many commands and capabilities of Linux we ve just scratched the surface Fedora and other dis tributions come with thousands of other programs We encourage you to continue reading exploring and learning the capabilities of your Linux systems Good luck Acknowledgments Heartfelt thanks to my editor Mike Loukides the O Reilly production staff the technical reviewers Ron Bellomo Wes ley Crossman David Debonnaire Tim Greer Jacob Heider and Eric van Oorsch
103. espond to finger requests only if they are configured to do so Useful options 1 Print in long format S Print in short format p Don t display the Project and Plan sections which are ordinarily read from the user s project and plan files respectively last options users ttys SysVinit usr bin stdin stdout file opt help version The last command displays a history of logins in reverse chrono logical order last barrett pts 3 localhost Mon Sep 8 21 07 21 08 00 01 smith pts 6 0 Mon Sep 8 20 25 20 56 00 31 barrett pts 4 myhost Sun Sep 7 22 19 still logged in You may provide usernames or tty names to limit the output Useful options N Print only the latest N lines of output where N is a positive integer i Display IP addresses instead of hostnames R Don t display hostnames X Also display system shutdowns and changes in system runlevel e g from single user mode into multiuser mode f filename Read from some other data file than var run utmp see the who command for more details printenv environment_variables coreutils usr bin stdin stdout file opt help version The printenv command prints all environment variables known to your shell and their values printenv HOME home smith MAIL var spool mail smith 114 Linux Pocket Guide NAME Sandy Smith SHELL bin bash or only specified variables printenv HOME SHELL home smith bin bas
104. ewer displays graphics files in a variety of formats If you invoke it for a single file it displays the file Invoked on two or more files eog file1 jpg file2 gif file3 pbm it displays each in a separate window Most eog options are fairly technical so we won t cover them we mention this so you know eog has options in case you want to investigate them eog help gqview options file gqview usr bin stdin stdout file opt help version The gqview image viewer displays graphics files in a variety of formats and can automatically switch from one image to the next like a slideshow By default it displays the names of all graphics files in the current directory and you can select names to display the images The onscreen menus are straightforward so explore them and try things out Type q to quit 160 Linux Pocket Guide Useful options f Display images in full screen mode Toggle between full screen mode and window mode by typing v S Display images in a slideshow Turn the slideshow on and off by typing s ksnapshot options kdegraphics usr bin stdin stdout file opt help version The ksnapshot command is a versatile screen capture utility Simply run ksnapshot and it takes a screenshot displaying it in miniature From there you can save it to a graphics file or take another screenshot The only subtlety is choosing a file format for the output this is done when you save b
105. f you supply a file or directory df describes the disk device on which that file or directory resides With no arguments df reports on all mounted filesystems df Filesystem 1k blocks Used Available Use Mounted on dev hda 1011928 225464 735060 24 dev hda9 521748 249148 246096 51 var dev hda8 amp 8064272 4088636 3565984 54 usr dev hda10 8064272 4586576 3068044 60 home Useful options k List all sizes in kilobytes the default or megabytes respectively m B N Display sizes in blocks that you define where 1 block N bytes Default 1024 h Print human readable output and choose the most appropriate unit for H each size For example if your two disks have 1 gigabyte and 25 kilobytes free respectively df h prints 1G and 25K The h option uses powers of 1024 whereas H uses powers of 1000 1 Display only local filesystems not networked filesystems T Include the filesystem type ext2 vfat etc in the output t type Display only filesystems of the given type x type Don t display filesystems of the given type lt i Inode mode Display total used and free inodes for each filesystem instead of disk blocks 92 Linux Pocket Guide mount options device directory mount bin stdin stdout file opt help version The mount command makes a hardware storage device accessible Most commonly it handles disk devices say dev hda1 making them accessible via an existing di
106. fault editor 52 egrep command 73 else statement 170 emacs text editor command line editing 28 creating editing files 51 54 lynx emacskeys command 138 RPM filenames and 35 email readers 132 135 environment variables 24 EDITOR 45 52 HOME 15 23 preserving in new shell 119 printing 114 VISUAL 45 52 eog Eye of Gnome image viewer 160 Epiphany web browser for GNOME 136 escaping special characters 27 Index 183 etc directory 16 evolution command 132 Excel documents editing with abiword 56 editing with soffice 55 exit command 12 exiting with return codes 178 terminating loops 174 terminating shells 33 exit status return codes of Linux commands 167 export command 24 expr command 149 ext3 filesystems 91 chattr Isattr commands 64 Eye of Gnome eog image viewer 160 F false command 170 infinite loops and 174 fdisk program 95 Fedora Linux 2 getting help with 8 graphical desktop 9 running shell windows 11 up2date command 34 fg command 32 jobs command and 30 fgrep command 74 file command 59 filename completion 29 files changing timestamps 60 copying using cp command 39 creating 51 56 deleting using rm command 39 editing 51 56 linking using In command 40 listing attributes of 57 listing using ls command 38 locating 65 71 measuring disk space of 59 moving 39 permissions ownership 19 38 62 64 renaming 39 setting group ownership of
107. fault group with a unique numeric group ID The id command prints these values along with their associated user and group names id uid 500 smith gid 500 smith groups 500 smith 6 disk 490 src 501 cdwrite Useful options u Print the effective user ID and exit g Print the effective group ID and exit G Print the IDs of all other groups to which the user belongs n Print names for users and groups rather than numeric IDs Must be combined with u g or G For example id Gn produces the same output as the groups command r Print real values instead of effective values Must be combined with u g or G who options filename coreutils usr bin stdin stdout file opt help version The who command lists all logged in users one user shell per line who smith 0 Sep 6 17 09 barrett pts 1 Sep 6 17 10 jones pts 2 Sep 8 20 58 jones pts 4 Sep 3 05 11 Normally who gets its data from the file var run utmp The filename argument can specify a different data file such as var log wtmp for past logins or var log btmp for failed logins Useful options H Print a row of headings as the first line 1 For remotely logged in users print the hostnames of origin If your system is configured to log those past or failed logins 112 Linux Pocket Guide u Also print each user s idle time at his her terminal T Also indicate whether each user s terminal is writable seemesg yin
108. ffect the given process ID You can omit the p and just provide a PID renice 5 28734 u username Affect all processes owned by the given user Users and Their Environment logname Print your login name whoami Print your current effective username id Print the user ID and group membership of a user 110 Linux Pocket Guide who List logged in users long output users List logged in users short output finger Print information about users last Determine when someone last logged in printenv Print your environment Who are you Only the system knows for sure This grab bag of programs tells you all about users their names login times and properties of their environment logname coreutils usr bin stdin stdout file opt help version The logname command prints your login name It might seem trivial but it s useful in shell scripts logname smith whoami coreutils usr bin stdin stdout file opt help version The whoami command prints the name of the current effective user This may differ from your login name the output of logname if you ve used the su command This example distin guishes whoami from logname logname smith whoami smith su Password KkEkkk logname smith whoami root Users and Their Environment 111 id options username coreutils usr bin stdin stdout file opt help version Every user has a unique numeric user ID and a de
109. files on the command line they must exist gnumeric won t create them for you File Properties stat Display attributes of files and directories wc Count bytes words lines in a file du Measure disk usage of files and directories file Identify guess the type of a file touch Change timestamps of files and directories Under the hood soffice comprises the separate programs Writer swriter command for word processing Calc scalc for spreadsheets and Impress simpress for presentations which you can run directly if desired 56 Linux Pocket Guide chown Change owner of files and directories chgrp Change group ownership of files and directories chmod Change protection mode of files and directories chattr Change extended attributes of files and directories Isattr List extended attributes of files and directories When examining a Linux file the contents are only half the story Every file and directory also has attributes that describe its owner size access permissions and other infor mation The 1s 1 command see Basic File Operations on page 37 displays some of these attributes but other com mands provide additional information stat options files coreutils usr bin stdin stdout file opt help version The stat command lists important attributes of files by default or filesystems f option File information looks like stat myfile File myfile Size 1264 Blocks 8 Regul
110. ft column indicates the file offset of the row the next eight columns contain the data and the final column displays the print able characters in the row if any xxd produces three column output by default file offsets the data in hex and the data as text printable characters only 48 Linux Pocket Guide Useful options 1 N Display only the first N bytes Default is to display the entire file s N Begin at a position other than the first byte of the file The first form skips the s N first N bytes The second N begins N bytes from the end of the file There is also a N syntax for more advanced skipping through standard input see the manpage c N Display N bytes per row Default 16 g N Group each row of bytes into sequences of N bytes separated by whitespace likeod s Default 2 b Display the output in binary instead of hexadecimal u Display the output in uppercase hexadecimal instead of lowercase p Display the output as a plain hexdump 60 contiguous bytes per line i Display the output as a C programming language data structure When reading from a file it produces an array of unsigned chars containing the data and an unsigned int containing the array length When reading from standard input it produces only a comma separated list of hex bytes Y The reverse operation convert from an xxd hex dump back into the original file format Works with the default hexdump format and if you add
111. ful options name pattern The name name pathname path or symbolic link path pattern target 1name of the desired file must match this shell Iname pattern pattern which may include shell wildcards and Paths are relative to the directory tree being searched The iname ipath and ilname options are the same as name path and name respectively but are case insensitive iname pattern ipath pattern ilname pattern regex regexp The path relative to the directory tree being searched must match the given regular expression The tcsh shell performs some trickery to make which detect aliases 66 Linux Pocket Guide type f d 1 b c p s atime N ctime N mtime N amin N cmin N mmin N anewer other file cnewer other file newer other file maxdepth N mindepth N follow depth xdev size N bckw empty user name group name perm mode perm mode perm mode Locate only plain files f directories d symbolic links 1 block devices b character devices c named pipes p or sockets s File was last accessed at ime last modified mtime or had a status change ct ime exactly N 24 hours ago Use N for greater than N or N for less than N File was last accessed amin last modified mmin or had a status change cmin exactly N minutes ago Use N for greater than N or N for less than N File was accesse
112. g octal o signed decimal d unsigned decimal u hexadecimal x For binary output use xxd instead SIZE represents the number of bytes per integer it can be a positive integer or any of the values C S or L which stand for the size of a char short int or long datatype respectively For z see below t f SIZE z Display output in floating point SIZE represents the number of bytes per integer it can be a positive integer or any of the values F D or L which stand for the size of a float double or long double datatype respectively For z see below If t is omitted the default is to2 Appending z to the t parameter prints a new column on the right hand side of the output displaying the printable characters on each line much like the default output of xxd xxd options files vim common usr bin stdin stdout file opt help version Similar to od xxd produces a hexadecimal or binary dump of a file in several different formats It can also do the reverse converting from its hex dump format back into the original data For example the command xxd usr bin who 0000000 7f45 4c46 0101 0100 0000 0000 0000 0000 ELF 0000010 0200 0300 0100 0000 a08c 0408 3400 0000 A e 0000020 6824 0000 0000 0000 3400 2000 0600 2800 h 4 0000030 1900 1800 0600 0000 3400 0000 3480 0408 4 4 displays a hex dump of binary file usr bin who 16 bytes per row The le
113. g to your instructions comm options file1 file2 coreutils usr bin stdin stdout file opt help version The comm command compares two sorted files and produces three columns of output separated by tabs 1 All lines that appear in file1 but not in file2 2 All lines that appear in file2 but not in file1 3 All lines that appear in both files For example if file1 and file2 contain these lines filel file2 apple baker baker charlie charlie dark then comm produces this output comm file1 file2 apple baker charlie dark 88 Linux Pocket Guide Useful options 1 Suppress column 1 2 Suppress column 2 3 Suppress column 3 cmp options file1 file2 offset1 offset2 diffutils usr bin stdin stdout file opt help version The cmp command compares two files If their contents are the same cmp reports nothing but if different it lists the location of the first difference cmp myfile yourfile myfile yourfile differ char 494 line 17 By default cmp does not tell you what the difference is only where it is It also is perfectly suitable for comparing binary files as opposed to diff which operates best on text files Normally cmp starts its comparison at the beginning of each file but it will start elsewhere if you provide offsets cmp myfile yourfile 10 20 This begins the comparison at the tenth character of myfile and the twentieth of yourfile Useful options
114. ge Send Receive Check for new mail Reply Reply to a message only to the sender Reply To All Reply to a message to all addresses in the To and CC lines Forward Forward a message to a third party There are many more features experiment mutt options mutt usr bin stdin stdout file opt help version mutt is a text based mailer that runs in an ordinary terminal or terminal window so it can be used both locally e g in an X terminal window or remotely over an SSH connection It is very powerful with many commands and options To invoke it type mutt When the main screen appears any messages in your mailbox are listed briefly one per line The commands in Table 4 are available Table 4 mutt commands available on the main screen Keystroke Meaning Up arrow Move to the previous message Down arrow Move to the next message PageUp Scroll up one pageful of messages PageDown Scroll down one pageful of messages Home Move to the first message End Move to the last message m Compose a new mail message This invokes your default text editor After editing the message and exiting the editor type y to send the message or q to postpone it Email 133 Table 4 mutt commands available on the main screen continued Keystroke Yr f i C d Meaning Reply to current message Works like m Forward the current message to a third party Works like m View the contents of your mailbox Copy the current
115. given program info displays the program s manpage For a listing of avail able documentation type info by itself To learn how to navigate the info system type info info Use the help option if any Many Linux commands respond to the option help by printing a short help message Try 1s help Examine the directory usr share doc This directory contains supporting documents for many programs usually organized by program name and ver sion For example files for the text editor Emacs Ver sion 21 3 are found in usr share doc emacs 21 3 GNOME and KDE Help For help with GNOME or KDE choose the Help item in the main menu Fedora specific web sites The official site is http fedora redhat com An unofficial FAQ has sprung up at http fedora artoo net And of course there s the web site for this book http www oreilly com cataloglinuxpg 8 Linux Pocket Guide Usenet newsgroups Usenet has dozens of newsgroups on Linux topics such as comp os linux misc and comp os linux questions For Red Hat specific information try alt os linux redhat comp os linux redhat linux redhat and linux redhat misc You can search through newsgroup postings at Google Groups http groups google com which is a goldmine of troubleshooting information Google Search Google for further documentation and tutorials at http www google com if you ve been living in a closet Fedora A First View When you log into a
116. h Working with User Accounts useradd Create a new account userdel Delete an account usermod Modify an account passwd Change a password chfn Change a user s personal information chsh Change a user s shell The Fedora installer prompts you to create two accounts one for the superuser and one for an ordinary user presumably yourself But you might want to create other accounts too Creating users is an important job not to be taken lightly Every account is a potential avenue for an intruder to enter your system so every user should have a strong hard to guess password and should change it regularly useradd options username shadow utils usr sbin stdin stdout file opt help version The useradd command lets the superuser create a new user account useradd smith Its defaults are not very useful run useradd D to see them so be sure to supply all desired options For example useradd d home smith s bin bash g users smith Working with User Accounts 115 Useful options d dir Set the user s home directory to be dir s shell Set the user s login shell to be she1J u uid Set the user s ID to be uid Unless you know what you re doing omit this option and accept the default g group Set the user s initial default group to group which can either be a numeric group ID or a group name and which must already exist G group1 group2 Make the user a member of the additiona
117. have a hamburger 3 sleep echo Good night then echo I m not sure what you want to do echo I guess I ll see you tomorrow 33 33 esac Programming with Shell Scripts 171 The general form is case string in expr1 body1 3 expr2 body2 35 exprN bodyN 35 bodyelse j5 esac where string is any value usually a variable value like myvar and expr1 through exprN are patterns run the com mand info bash reserved case for details with the final like a final else Each set of commands must be terminated by as shown case letter in xX echo letter is an X a gt aeiou echo letter is a vowel 33 0 9 echo letter is a digit silly 33 echo I cannot handle that 33 esac Loops The while loop repeats a set of commands as long as a condi tion is true while command While the exit status of command is 0 do body done 172 Linux Pocket Guide For example if this is the script myscript i 0 while i lt 3 do echo i i expr i 1 done myscript NP OW The until loop repeats until a condition becomes true until command While the exit status of command is nonzero do body done For example i 0 until i ge 3 do echo i i expr i 1 done myscript 0 1 2 The for loop iterates over values from a list for variable in list do body done For example for name in Tom Jack Harry do echo
118. he foreground suspend The built in command suspend will suspend the current shell if possible as if you d typed Z to the shell itself For instance if you ve run the su command and want to return to your original shell whoami smith su 1 Password whoami root suspend 1 Stopped su whoami smith bg jobnumber The built in command bg sends a suspended job to run in the background With no arguments bg operates on the most recently suspended job To specify a particular job shown by the jobs command supply the job number preceded by a percent sign bg 2 The Shell 31 Some types of interactive jobs cannot remain in the background for instance if they are waiting for input If you try the shell will suspend the job and display 2 Stopped command line here You can now resume the job with fg and continue fg jobnumber The built in command fg brings a suspended or backgrounded job into the foreground With no arguments it selects a job usually the most recently suspended or backgrounded one To specify a particular job as shown by the jobs command supply the job number preceded by a percent sign fg 2 Killing a Command in Progress If you ve launched a command from the shell running in the foreground and want to kill it immediately type C The shell recognizes C as meaning terminate the current foreground command right no
119. headers and footers Useful options b a t n pR Prepend numbers to all lines a nonblank lines t no lines n or only lines that contain regular expression R Default a v N Begin numbering with integer N Default 1 i N ncrement the number by N for each line so for example you could use odd numbers only i2 or even numbers only v2 i2 Default 1 n 1n rn rz Format numbers as left justified 1n right justified xn or right justified with leading zeroes rz Default 1n w N Force the width of the number to be N columns Default 6 s S nsert string S between the line number and the text Default TAB 46 Linux Pocket Guide Additionally nl has the wacky ability to divide text files into virtual pages each with a header body and footer with different numbering schemes For this to work however you must insert nl specific delimiter strings into the file start of header start of body and start of footer Each must appear on a line by itself Then you can use additional options see the manpage to affect line numbering in the headers and footers of your decorated file od options files coreutils usr bin stdin stdout file opt help version When you want to view a binary file consider od Octal Dump for the job It copies one or more files to standard output displaying their data in ASCII octal decimal hexadecimal or floating point in various siz
120. hysical file on disk in tech talk it points to the same inode Deleting the original file does not invalidate the link lIn myfile hardlink Symbolic links can cross disk partitions since they are just refer ences to file paths hard links cannot since an inode on one disk has no meaning on another Symbolic links can also point to directories whereas hard links cannot unless you are the super user and use the d option Useful options S Make a symbolic link The default is a hard link i Interactive mode Ask before overwriting destination files ef Force the link If a destination file exists overwrite it unconditionally d Allow the superuser to create a hard link to a directory 40 Linux Pocket Guide It s easy find out where a symbolic link points with either of these commands readlink linkname 1s 1 linkname Directory Operations cd Change your current directory pwd Print the name of your current directory i e where you are now in the filesystem basename Print the final part of a file path dirname Remove the final part of a file path mkdir Create a directory rmdir Delete an empty directory rm r Delete a nonempty directory and its contents We discussed the directory structure of Linux in The Filesys tem on page 13 Now we ll cover commands that create mod ify delete and manipulate directories within that structure cd directory bash shell built in stdin
121. ic links reporting the type of the destination file instead of the link Z If a file is compressed see File Compression and Packaging on page 82 examine the uncompressed contents to decide the file type instead of reporting compressed data touch options files coreutils bin stdin stdout file opt help version The touch command changes two timestamps associated with a file its modification time when the file s data was last changed and its access time when the file was last read touch myfile You can set these timestamps to arbitrary values e g touch d November 18 1975 myfile If a given file doesn t exist touch creates it a handy way to create empty files Useful options a Change the access time only m Change the modification time only C If the file doesn t exist don t create it normally touch creates it 60 Linux Pocket Guide d timestamp Set the file s timestamp s A tremendous number of timestamp formats are acceptable from 12 28 2001 3pm to 28 May the current year is assumed and a time of midnight to next tuesday 13 59 to 0 midnight today Experiment and check your work with stat Full documentation is available from info touch t timestamp Aless intelligent way to set the file s timestamp using the format CC YY MMDDhhmm s s where CC is the two digit century YY is the two digit year MM is the 2 digit month DD is the
122. ice In s dev hto dev tape Backups and Remote Storage 95 We aren t presenting every Linux command for backups Some users prefer cpio to tar and for low level disk copies dd is invaluable See the manpages for these programs if you are interested in them mt f device command mt st bin stdin stdout file opt help version The mt magnetic tape command performs simple operations on a tape drive such as rewinding skipping forward and backward and retensioning Some common operations are status Show the status of the drive rewind Rewind the tape retension Retension the tape erase Erase the tape offline Take the tape drive offline eod Move forward on the tape to the end of data For example mt f dev tape rewind You can also move through the tape file by file or record by record but often you ll use a tape reading writing program for that such as tar or restore dump options partition_or_files dump sbin stdin stdout file opt help version The dump command writes an entire disk partition or selected files to a backup medium such as tape It supports full and incre mental backups automatically figuring out which files need to be backed up i e which have changed since the last backup To restore files from the backup medium use the restore command To perform a full backup of a given filesystem say usr to your tape device say dev tape use the 0 zero
123. iewing the contents head myfile head less Preview all files in the current directory Useful options N Print the first N lines instead of 10 nN c N Print the first N bytes of the file q Quiet mode when processing more than one file don t print a banner above each file Normally head prints a banner containing the filename File Viewing 45 tail options files coreutils usr bin stdin stdout file opt help version The tail command prints the last 10 lines of a file and does other tricks as well tail myfile Useful options N Print the last N lines of the file instead of 10 n N N Print all lines except the first N c N Print the last N bytes of the file f Keep the file open and whenever lines are appended to the file print them This is extremely useful Add the retry option if the file doesn t exist yet but you want to wait for it to exist q Quiet mode when processing more than one file don t print a banner above each file Normally tail prints a banner containing the filename nl options files coreutils usr bin stdin stdout file opt help version nl copies its files to standard output prepending line numbers It s more flexible than cat with its n and b options providing an almost bizarre amount of control over the numbering nl can be used in two ways on ordinary text files and on specially marked up text files with predefined
124. ill found on some Linux and Unix systems Host Location 125 whois options domain_name jwhois usr bin stdin stdout file opt help version The whois command looks up the registration of an Internet domain whois redhat com Registrant Red Hat Inc REDHAT DOM P O Box 13588 Research Triangle Park NC 27709 These days you ll see a few screensful of legal disclaimers from the registrar before or after the real information appears Useful options h registrar Perform the lookup at the given registrar s server For example whois h whois networksolutions com yahoo com p port Query the given the TCP port instead of the default 43 the whois service ping options host iputils bin stdin stdout file opt help version The ping command tells you if a remote host is reachable It sends small packets ICMP packets to be precise to a remote host and waits for responses ping google com PING google com 216 239 37 100 from 192 168 0 10 56 84 bytes of data 64 bytes from www google com 216 239 37 100 icmp_seq 0 ttl 49 time 32 390 msec 64 bytes from www google com 216 239 37 100 icmp seq 1 ttl 49 time 24 208 msec SE google com ping statistics 2 packets transmitted 2 packets received 0 packet loss round trip min avg max mdev 24 208 28 299 32 390 4 091 ms Useful options c N Ping at most N times 126 Linux Pocket Guide iN Wait N seconds default 1 betw
125. ils bin stdin stdout file opt help version The simplest viewer is cat which just copies its files to standard output concatenating them hence the name Note that large files will likely scroll off screen so consider using less if you plan to view the output That being said cat is particularly useful for sending a set of files into a shell pipeline FileViewing 43 cat can also manipulate its output in small ways optionally displaying nonprinting characters prepending line numbers though nl is more powerful for this purpose and eliminating whitespace Useful options T Print tabs as l E Print newlines as v Print other nonprinting characters in a human readable format n Prepend line numbers to every line b Prepend line numbers to nonblank lines S Squeeze each sequence of blank lines into a single blank line less options files less usr bin stdin stdout file opt help version Use less to view text one page at a time or one window or screenful at a time Its great for text files or as the final command in a shell pipeline with lengthy output command1 command2 command3 command4 less While running less type h for a help message describing all its features Here are some useful keystrokes for paging through files Keystroke Meaning h H View a help page Spacebar f V F Move forward one screenful Enter Move forward one line b B ESC b Move backwa
126. in the year in our example September 1 would be displayed as 244 September 2 as 245 and so on date options format coreutils bin stdin stdout file opt help version The date command prints dates and times By default it prints the system date and time in the local timezone date Sun Sep 28 21 01 31 EDT 2003 You can format the output differently by supplying a format string beginning with a plus sign date D 09 28 03 date The time is 1 M p on a beautiful A in B The time is 9 01 PM on a beautiful Sunday in September Format Meaning Example Whole dates and times c Full date and time 12 hour clock Sun 28 Sep 2003 09 01 25 PM EDT D Numeric date 2 digit year 09 28 03 x Numeric date 4 digit year 09 28 2003 T Time 24 hour clock 21 01 25 Datesand Times 153 Format Meaning Example X Time 12 hour clock 09 01 25 PM Words a Day of week abbreviated Sun A Day of week complete Sunday b Month name abbreviated Sep B Month name complete September Z Time zone EDT p AM or PM PM Numbers OW Day of week 0 6 0 Sunday 0 u Day of week 1 7 1 Monday 7 d Day of month leading zero 02 e Day of month leading blank 2 j Day of year leading zeroes 005 m Month number leading zero 09 y Year 2 digits 03 Y Year 4 digits 2003 M Minute leading zero 09 S Seconds leading zero 05 1 Hour 12 hour clock leading blank 9 I Hour 12 hour clock leading ze
127. ing for your command Options may be given individually myprogram a b c myfile Three individual options or combined behind a single dash myprogram abc myfile Same as a b c though some programs are quirky and do not recognize com bined options Commands can also be much more complex than running a single program e They can run several programs at once either in sequence one after the other or connected into a pipe line with the output of one command becoming the input of the next Red Hat now focuses on its Enterprise Linux products for higher end appli cations Most of this book applies to Enterprise and other Linux distros What s in This Book 3 e Options are not standardized The same option say 1 may have different meanings to different programs in wc 1 it means count lines of text but in 1s 1 it means produce longer output In the other direction two pro grams might use different options to mean the same c thing such as q for run quietly versus s for run silently e Likewise arguments are not standardized They often rep resent filenames for input or output but they can be other things too like directory names or regular expressions e The Linux command line user interface the shell has a programming language built in So instead of a com mand saying run this program it might say if today is Tuesday run this program otherwise run a
128. ing processes for advanced users The files in proc provide views into the running kernel and have special properties They always appear to be zero sized read only and dated now Is 1 proc version r rY r 1 root root O Oct 3 22 55 proc version However their contents magically contain information about the Linux kernel cat proc version Linux version 2 4 22 1 2115 nptl Mostly these files are used by programs Go ahead and explore Here are some examples 18 Linux Pocket Guide proc ioports A list of your computer s input output hardware proc version The operating system version The uname command prints the same information proc uptime System uptime i e seconds elapsed since the system was last booted Run the uptime command for a more human readable result proc nnn Where nnn is a positive integer information about the Linux process with process ID nnn proc self Information about the current process you re running a symbolic link toa proc nnn file automatically updated Try 1s 1 proc self a few times in a row you ll see proc self changing where it points File Protections A Linux system may have many users with login accounts To maintain privacy and security each user can access only some files on the system not all This access control is embodied in two questions Who has permission Every file and directory has an owner who has permission to do anything with it Typically
129. ion The uptime command tells you how long the system has been running since the last boot uptime 10 54pm up 8 days 3 44 3 users load average 0 89 1 00 2 15 This information is from right to left the current time 10 54pm system uptime 8 days 3 hours 44 minutes number of users Viewing Processes 105 logged in 3 and system load average for three time periods one minute 0 89 five minutes 1 00 and fifteen minutes 2 15 The load average is the average number of processes ready to run in that time interval Ww username procps usr bin stdin stdout file opt help version The w command displays the current process for each logged in user or more specifically for each shell of each user w 10 51pm up 8 days 3 42 8 users load average 0 00 0 00 0 00 USER TTY FROM LOGIN IDLE JCPU PCPU WHAT barrett pts 0 0 Sat 2pm 27 13m 0 07s 0 07s emacs jones pts 1 host1 6Sep03 2 33m 0 74s 0 21s bash smith pts 2 host2 6Sep03 0 00s 13 35s 0 045 w The top line is the same one printed by uptime The columns indi cate the user s terminal originating host or X display if applicable login time idle time two measures of the CPU time run man w for details and the current process Provide a user name to see only that user s information For the briefest output try w hfs Useful options h Don t print the header line f Don t print the FROM column sS Don t print the JCPU
130. ions are hdd 1 hdd2 sda First SCSI device partitions are sda 1 sda2 sdb Second SCSI device partitions are sdb 1 sdb2 Likewise for sdc sdd hto First IDE tape drive then ht7 ht2 with auto rewind nhto First IDE tape drive then nht7 nht2 without auto rewind stO First SCSI tape drive then st7 st2 scdO First SCSI CD ROM drive then scd7 scd2 fdo First floppy drive then fd 1 fd2 usually mounted on mnt floppy Before a partition can hold files it is formatted by writing a filesystem on it A filesystem defines how files are repre sented examples are ext3 Linux journaling filesystem the Fedora default and vfat Microsoft Windows filesystem Formatting is generally done for you when installing Linux Disks and Filesystems 91 Once a filesystem is created you can make it available for use by mounting it on an empty directory For example if you mount a Windows filesystem on a directory mnt win it becomes part of your system s directory tree and you can create and edit files like mnt win myfile Filesystems can also be unmounted to make them inaccessible say for mainte nance Mounting of hard drives is generally done automati cally at boot time df options disk devices files directories coreutils bin stdin stdout file opt help version The df disk free program shows you the size used space and free space on a given disk partition I
131. issions for all other users We describe ls in more detail in Basic File Operations on page 37 To change the owner group ownership or permis sions of a file use the chown chgrp and chmod commands respectively as described in File Properties on page 56 The Shell In order to run commands on a Linux system you ll need somewhere to type them That somewhere is called the shell which is Linux s command line user interface you type a command and press Enter and the shell runs whatever pro gram or programs you ve requested To run a shell see Fedora A First View on page 9 For example to see who s logged in you could execute this command in a shell who barrett 0 Sep 23 20 44 byrnes pts 0 Sep 15 13 51 silver pts 1 Sep 22 21 15 silver pts 2 Sep 22 21 18 20 Linux Pocket Guide The dollar sign is the shell prompt which means the shell is ready to run a command A single command can also invoke several programs at the same time and even connect pro grams together so they interact Here s a command that redi rects the output of the who program to become the input of the wc program which counts lines of text in a file the result is the number of lines in the output of who who wc 1 4 telling you how many users are logged in The vertical bar called a pipe makes the connection between who and wc A shell is actually a program itself and Linux has several We foc
132. l existing groups group1 group2 and so on m Copy all files from your system skeleton directory etc skel into the newly created home directory The skeleton directory traditionally contains minimal skeletal versions of initialization files like bash_profile to get new users started If you prefer to copy from a different directory add the k option k your_preferred_ directory userdel r username shadow utils usr sbin stdin stdout file opt help version The userdel command deletes an existing user userdel smith It does not delete the files in the user s home directory unless you supply the r option Think carefully before deleting a user consider deactivating the account instead with usermod L And make sure you have backups of all the user s files before deleting them you might need them again someday usermod options username shadow utils usr sbin stdin stdout file opt help version The usermod command modifies the given user s account in various ways like changing a home directory usermod d home another smith Useful options d dir Change the user s home directory to dir 116 Linux Pocket Guide l username Change the user s login name to username Think carefully before doing this in case anything on your system depends on the original name And definitely don t do it to system accounts root daemon and so on s shell Change the user s login sh
133. l execution time so wildcards variables and other shell constructs are not expanded until then Also your current environment see printenv is preserved within each job so it executes as if you were logged in Aliases however aren t available to at jobs so don t include them To list your at jobs use atq at queue atq 559 2003 09 14 07 00 a smith To delete an at job run atrm at remove with the job number atrm 559 Useful options f filename Read commands from the given file instead of standard input c job_number Print the job commands to standard output Programmers can read the precise syntax in usr share doc at timespec Scheduling Jobs 157 crontab options file vixie cron usr bin stdin stdout file opt help version The crontab command like at schedules jobs for specific times However crontab is for recurring jobs such as Run this command at midnight on the second Tuesday of each month To make this work you edit and save a file called your crontab file crontab e which automatically gets installed in a system directory var spool cron Once a minute a Linux process called cron wakes up checks your crontab file and executes any jobs that are due crontab e Edit your crontab file in your default editor EDITOR crontab 1 Print your crontab file on standard output crontab r Delete your crontab file crontab myfile Install th
134. ld mail s subject smith example com To mail a file using a single command use either of these mail s my subject smith example com lt filename cat filename mail s my subject smith example com Notice how easily you can send the output of a pipeline as an email message Useful options s subject Set the subject line of an outgoing message v Verbose mode print messages about mail delivery c addresses Cthe message to the given addresses a comma separated list b addresses BCC the message to the given addresses a comma separated list On older Unix systems Mail and mail were rather different programs but on Linux they are the same usr bin Mail is a symbolic link to bin mail Email 135 Web Browsing mozilla Full featured web browser lynx Text only web browser wget Retrieve web pages to disk curl Retrieve web pages to disk Linux offers several ways to explore the World Wide Web traditional browsers text based browsers and page retrieval utilities mozilla options URL mozilla usr bin stdin stdout file opt help version Mozilla is one of the most popular web browsers for Linux it runs on most other operating systems as well including an X window Start it in the background with mozilla amp Mozilla provides features you d expect browsing forward and back buttons bookmarks history and so on plus tabbed browsing pop up window suppression and much
135. lrn but there are dozens more available on the Net rn trn tin and so on Mozilla also can read Usenet News from the Window menu choose Mail amp Newsgroups Usenet News can also be searched at Google Groups http groups google com In order to access Usenet you need to connect to a news server an Internet host that permits reading and posting of news articles Once you can connect to a news server say news example com a record of your subscribed newsgroups and which articles you ve read is kept in a file in your home directory automatically Depending on your newsreader con figuration the file is either newsrc or jnewsrc slrn options sirn usr bin stdin stdout file opt help version slrn is a Usenet newsreader Before using it you must specify a news server by setting your shell s NNTPSERVER variable export NNTPSERVER news example com Then create a newsgroups file only if you haven t used slrn on this computer before slrn create and start reading news slrn 140 Linux Pocket Guide When invoked slrn displays the News Groups page with a list of your subscribed newsgroups Table7 shows some useful commands Table 7 Usenet slrn keystrokes for newsgroups Keystroke Meaning q Quit slrn Down Select next newsgroup Up Select previous newsgroup Enter Read the selected newsgroup p Post a new article in the selected newsgroup a Add a new newsgroup you must know th
136. ls ld newfile dir IW 1 smith smith O Nov 11 12 27 newfile drwx 2 smith smith 4096 Nov 11 12 27 dir soffice files openoffice org usr lib openoffice programs stdin stdout file opt help version OpenOffice org is a comprehensive integrated office software suite that can edit Microsoft Word Excel and PowerPoint files Simply run soffice The org is part of the software package s name File Creation and Editing 55 and you re ready to work The same program edits all three types of files It is a large program that requires plenty of memory and disk space OpenOffice org can also handle drawings sdraw command faxes sfax mailing labels slabel and more http www openoffice org has more information or you can use the soffice Help menu abiword options files abiword usr bin stdin stdout file opt help version abiword is another program for editing Microsoft Word docu ments It is smaller and quicker than soffice though not as powerful and perfectly suitable for many editing tasks If you specify files on the command line they must exist abiword won t create them for you gnumeric options files gnumeric usr bin stdin stdout file opt help version gnumeric is a spreadsheet program that can edit Microsoft Excel documents It is quite powerful and fast and if you ve used Excel before gnumeric will feel familiar If you specify
137. micolons command1 command2 command3 26 Linux Pocket Guide To run a sequence of commands as above but stop execu tion if any of them fails separate them with amp amp and symbols command1 amp amp command2 amp amp command3 To run a sequence of commands stopping execution as soon as one succeeds separate them with or symbols command1 command2 command3 Quoting Normally the shell treats whitespace simply as separating the words on the command line If you want a word to con tain whitespace e g a filename with a space in it surround it with single or double quotes to make the shell treat it as a unit Single quotes treat their contents literally while double quotes let shell constructs be evaluated such as variables echo The variable HOME has value HOME The variable HOME has value HOME echo The variable HOME has value HOME The variable HOME has value home smith Backquotes cause their contents to be evaluated as a com mand the contents are then replaced by the standard output of the command usr bin whoami smith echo My name is usr bin whoami My name is smith Escaping If a character has special meaning to the shell but you want it used literally e g as a literal asterisk rather than a wild card precede the character with the backward slash character This is called escaping the special character echo a As a wildca
138. nce Look t i big prints all words beginning with bi aspell options file command aspell usr bin stdin stdout file opt help version aspell is a powerful spellchecker with dozens of options A few useful commands are aspell c file Interactively check and optionally correct the spelling of all words in file aspell 1 lt file Print a list of the misspelled words in file on standard output aspell dump master Print aspell s master dictionary on standard output aspell help Print a concise help message See http aspell net for more information Spelling Operations 103 spell files aspell usr bin stdin stdout file opt help version The spell command prints all words in the given files that are misspelled according to its dictionary It s the same as cat files aspell 1 sort u If no files are supplied spell reads from standard input Viewing Processes ps List process uptime View the system load w List active processes for all users top Monitor resource intensive processes interactively xload Monitor system load graphically in an X window free Display free memory A process is a unit of work on a Linux system Each program you run represents one or more processes and Linux pro vides commands for viewing and manipulating them Every process is identified by a numeric process ID or PID Processes are not the same as jobs see Job Control on
139. ne who executes F becomes a member of the friends group for the duration of the program As you might imagine setuid and setgid can impact system security so don t use them unless you really know what you re doing One misplaced chmod s can leave your whole system vulnerable to attack Conditional execute permission X means the same as x except that it succeeds only if the file is already executable or if the file is a directory Otherwise it has no effect Useful options R Recursively change the ownership within a directory hierarchy chattr options attributes files e2fsprogs usr bin stdin stdout file opt help version If you grew up with other Unix systems you might be surprised that Linux files can have additional attributes beyond their access permissions If a file is on an ext2 or ext3 filesystem the Fedora default you can set these extended attributes with the chattr change attribute command and list them with 1sattr As with chmod attributes may be added or removed rela tively or set absolutely Attribute Meaning a Append only appends are permitted to this file but it cannot otherwise be edited Root only A Accesses not timestamped accesses to this file don t update its access timestamp atime c Compressed data is transparently compressed on writes and uncompressed on reads d Don t dump tell the dump program to ignore this file when making backups see Backu
140. nes are emacs from the Free Software Foundation and vim a successor to the Unix editor vi Teaching these editors fully is beyond the scope of this book but both have online tutorials and we list com mon operations in Table 1 To edit a file run either emacs myfile vim myfile If myfile doesn t exist it is created automatically You can also quickly create an empty file for later editing using the touch command see File Properties on page 56 touch newfile or write data into a new file by redirecting the output of a program see Input output redirection on page 26 echo anything at all gt newfile File Creation and Editing 51 In case you share files with Microsoft Windows systems we will also cover Linux programs that edit Microsoft Word Excel and PowerPoint documents Your Default Editor Various Linux programs will run an editor when necessary and by default the editor is vim For example your email pro gram may invoke an editor to compose a new message and less invokes an editor if you type v But what if you don t want vim to be your default editor Set the environment vari ables VISUAL and EDITOR to your choice for example EDITOR emacs VISUAL emacs export EDITOR VISUAL Optional Both variables are necessary because different programs check one variable or the other Set EDITOR and VISUAL in your bash_profile startup file if you want your choices made perm
141. ng language Evaluate both expressions and return the value of the second one Once you ve specified the search criteria you can tell find to perform these actions on files that match the criteria Useful options print Simply print the path to the file relative to the search directory printf string Print the given string which may have substitutions applied to it in the manner of the C library function printf See the manpage for the full list of outputs printo Like print but instead of separating each line of output with a newline character use a null ASCII 0 character Use this when you are piping the output of find to another program and your list of filenames may contain space characters Of course the receiving program must be capable of reading and parsing these null separated lines for example xargs 0 exec cmd Invoke the given shell command cmd Make sure to escape any ok cmd shell metacharacters including the required final semicolon so they are not immediately evaluated on the command line Also the symbol make sure to quote or escape it represents the path to the file found The ok action prompts the user before invoking the shell command exec does not 1s Perform 1s dils onthe file find which produces a list of files on standard output makes a great partner with xargs which reads a list of files on standard input and applies a command to them see man xargs For
142. noia usr bin stdin stdout file opt help version The cdparanoia command reads rips audio data from a CD and stores it in WAV files or other formats see the manpage Common uses are cdparanoia N Rip track N to a file cdparanoia B Rip all tracks on the CD into separate files cdparanoia B 2 4 Rip tracks 2 3 and 4 into separate files cdparanoia 2 4 Rip tracks 2 3 and 4 into a single file If you have difficulty accessing your drive try running cdparanoia Ovs search for CD ROM drives verbosely and look for clues To convert your WAV files to MP3 format check out LAME http lame sourceforge net or NotLame http www idiap ch sanders not_lame xmms options files xmms usr bin stdin stdout file opt help version xmms X MultiMedia System is an excellent graphical audio file player that supports MP3 WAV Ogg Vorbis and other audio formats You can play files with familiar CD player controls create playlists and more The easiest way to get started is to try it either with no arguments xmms or providing audio files on the command line xmms file1 mp3 file2 wav file3 ogg Here are some useful actions Action Meaning Right click on titlebar Display main menu Click PL button Display playlist click Add to add files Fedora includes xmms without MP3 support visit http www xmms org to restore it or to install the latest untainted version 164
143. nother com mand six times for each file whose name ends in txt Users and Superusers Linux is a multiuser operating system On a given computer each user is identified by a unique username like smith or funkyguy and owns a reasonably private part of the sys tem for doing work There is also a specially designated user with username root who has the privileges to do anything at all on the system Ordinary users are restricted though they can run most programs in general they can modify only the files they own The superuser on the other hand can create modify or delete any file and run any program Some commands in this book can be run successfully only by the superuser In this case we use a hash mark as the shell prompt command goes here Otherwise we will use the dollar sign prompt indicating an ordinary user command goes here 4 Linux Pocket Guide To become the superuser you needn t log out and log back in just run the su command see Becoming the Superuser on page 118 and provide the superuser password su 1 Password Reading This Book When we describe a command we first present its general usage information For example the wc word count pro gram has the general usage wc options files which means you d type wc followed if you choose by options and then filenames You wouldn t type the square brackets and
144. ntf Print formatted text on standard output yes Print repeated text on standard output seq Print a sequence of numbers on standard output clear Clear the screen or window Linux provides several commands for printing messages on standard output in case you like to talk to yourself echo hello world hello world Each command has different strengths and intended pur poses These commands are invaluable for learning about At press time mesg y on Fedora fails with the error message tty device is gt not owned by group tty We expect this problem will get sorted out 144 Linux Pocket Guide Linux debugging problems and writing shell scripts see Programming with Shell Scripts on page 166 echo options strings bash shell built in stdin stdout file opt help version The echo command simply prints its arguments echo We are having fun We are having fun Unfortunately there are several different echo commands with slightly different behavior There s bin echo but Linux shells typi cally override this with a built in command called echo To find out which you re using run the command type echo Useful options n Don t print a final newline character e Recognize and interpret escape characters For example try echo hello a andecho e hello a The first prints literally and the second makes a beep E Don t interpret escape characters the opposite of e
145. nux Various distros includ ing Fedora simplify these interfaces so users can edit files read email and browse the Web without much effort Nevertheless the true power of Linux lies behind the scenes To get the most out of Linux you should become proficient Depending on your system configuration the interface might look differ ent GNOME and KDE are very configurable and Fedora includes a third interface twm with yet another look and feel And Linux has other graph ical interfaces too 10 Linux Pocket Guide in using the shell It might initially be more difficult than icons and menus but once you re used to it the shell is quite easy to use and very powerful Most of this book discusses Linux commands run via the shell How to Runa Shell To run a shell within GNOME KDE or any other graphical interface for Linux you ll need to open a shell window This is done by programs like xterm gnome terminal konsole and uxterm Each of these programs does the same basic thing open a window that is running a shell awaiting your input To run a shell window using the three default windowing interfaces for Fedora Interface Take this action to run this shell window program GNOME Menu System Tools Terminal gnome terminal or on the desktop Right Mouse Button Open Terminal KDE Menu System Tools Terminal konsole or on the desktop Right Mouse Button Open Terminal twm On the desktop xterm Right M
146. o use this option only if you know the remote file hasn t changed Try N times before giving up N 0 means try forever Print dots or bars to show the download progress Don t do any downloading just check the existence of the remote pages Retrieve all files into the current directory even if remotely they are in a more complex directory tree By default wget duplicates the remote directory hierarchy Retrieve a page hierarchy recursively all directories and subdirectories Retrieve files at most N levels deep 5 by default In all retrieved files modify links so pages can be viewed locally Download all necessary files to make a page display completely such as stylesheets and images Follow relative links within a page but not absolute links Accept mode download only files whose names match a given pattern Patterns may contain the same wildcards as the shell Reject mode download only files whose names do not match a given pattern Web Browsing 139 I patterni pattern2 Directory inclusion download files only from directories pattern3 that match a given pattern X Directory exclusion download files only from directories that do not match a given pattern Usenet News Usenet News is one of the oldest communities online today It consists of tens of thousands of newsgroups discussion forums in which people post submit messages and reply to them Fedora includes the newsreader s
147. often the default for user accounts However all these shells have similar basic functions A graphical system that provides windows menus icons mouse support and other familiar GUI elements More complex graphical environments are built on X the most popular are KDE and GNOME Throughout this book we discuss programs that open their own X windows to run What s Fedora Linux Fedora Linux is one particular Linux distribution or distro created by Red Hat Inc and the Fedora project for more 2 Linux Pocket Guide information see http fedora redhat com and formerly called Red Hat Linux Our material is based on Fedora Core 1 the first official release November 2003 We focus on the sup plied programs and the shell with brief coverage of X and the kernel as needed What s a Command A Linux command typically consists of a program name fol lowed by options and arguments typed within a shell The program name refers to a program somewhere on disk which the shell will locate and run Options which usually begin with a dash affect the behavior of the program and arguments usually represent inputs and outputs For exam ple this command to count the lines in a file wc 1 myfile consists of a program wc the word count program an option 1 saying to count lines and an argument myfile indicating the file to read The dollar sign is a prompt from the shell indicating that it is wait
148. ome directory These are not equivalent since Linux filenames are case sensitive 14 Linux Pocket Guide HOME variable The environment variable HOME see Shell variables on page 23 contains the name of your home directory echo HOME The echo command prints its arguments home smith When used in place of a directory a lone tilde is expanded by the shell to the name of your home directory echo home smith When followed by a username as in smith the shell expands this string to be the user s home directory cd smith pwd The print working directory command home smith System Directories A typical Linux system has tens of thousands of system direc tories These directories contain operating system files appli cations documentation and just about everything except private user files which typically live in home Unless you re a system administrator you ll rarely visit most system directories but with a little knowledge you can understand or guess their purposes Their names often con tain three parts which we ll call the scope category and application These are not standard terms but they ll help you understand things For example the directory usr local share emacs which contains local data for the Emacs text editor has scope usr local locally installed system files cat egory share program specific data and documentation and application emacs a text e
149. on page 33 to be available whenever you log in To see all your aliases type alias If aliases don t seem powerful enough for you since they have no parameters or branching see The Shell 25 Programming with Shell Scripts on page 166 run info bash and read up on shell functions Input output redirection The shell can redirect standard input standard output and standard error to and from files In other words any com mand that reads from standard input can have its input come from a file instead with the shell s lt operator mycommand lt infile Likewise any command that writes to standard output can write to a file instead mycommand gt outfile Create overwrite outfile mycommand gt gt outfile Append to outfile A command that writes to standard error can have its output redirected to a file as well mycommand 2 gt errorfile To redirect both standard output and standard error to files mycommand gt outfile 2 gt errorfile Separate files mycommand gt outfile 2 gt amp 1 Single file Pipes Using the shell you can redirect the standard output of one command to be the standard input of another using the shell s pipe operator For example who sort sends the output of who into the sort program printing an alphabetically sorted list of logged in users Combining commands To invoke several commands in sequence on a single com mand line separate them with se
150. onsibility for errors or omissions or for damages resulting from the use of the information contained herein 0 596 00628 4 C 4 06 What s in This Book What s Linux What s Fedora Linux What s a Command Users and Superusers Reading This Book Getting Help Fedora A First View The Role of the Shell How to Run a Shell Logins Logouts and Shutdowns The Filesystem Home Directories System Directories Operating System Directories File Protections The Shell The Shell Versus Programs Selected bash Features Job Control Contents aA UNN O oO N 13 14 15 18 19 20 21 21 29 Killing a Command in Progress Terminating a Shell Tailoring Shell Behavior Installing Software Basic File Operations Directory Operations File Viewing File Creation and Editing File Properties File Location File Text Manipulation File Compression and Packaging File Comparison Disks and Filesystems Backups and Remote Storage File Printing Spelling Operations Viewing Processes Controlling Processes Users and Their Environment Working with User Accounts 32 33 33 33 37 41 43 51 56 65 71 82 86 91 95 101 102 104 108 110 115 vi Contents Becoming the Superuser Working with Groups Basic Host Information Host Location Network Connections Email Web Browsing Usenet News Instant Messaging Screen Output Math and Calculations Dates and Times Scheduling
151. or megabytes m B N Display sizes in blocks that you define where 1 block N bytes Default 1024 h H Print human readable output and choose the most appropriate unit for each size For example if two directories are of size 1 gigabyte or 25 kilobytes respectively du h prints 1G and 25K The h option uses powers of 1024 whereas H uses powers of 1000 C Print a total in the last line This is the default behavior when measuring a directory but for measuring individual files provide c if you want a total L Follow symbolic links and measure the files they point to sS Print only the total size file options files file usr bin stdin stdout file opt help version The file command reports the type of a file file etc hosts usr bin who letter doc etc hosts ASCII text File Properties 59 usr bin who ELF 32 bit LSB executable Intel 80386 letter doc Microsoft Office Document Unlike some other operating systems Linux does not keep track of file types so the output is an educated guess based on the file content and other factors Useful options b Omit filenames left column of output i Print MIME types for the file such as text plain or audio mpeg instead of the usual output f name file Read filenames one per line from the given name_ file and report their types and afterward process filenames on the command line as usual L Follow symbol
152. orials 7 help option 8 hexadecimal dump of binary files 48 history command 29 home directories 14 HOME environment variable 15 23 host command 124 hostname command 122 html directory 16 id command 112 if statement 170 ifconfig command 123 if then elif else statement 171 Impress program soffice 56 include directory 16 index of file locations creating 69 info command 8 init d directory 16 input in shell scripts 167 input output redirection 26 installing software on the Linux system 33 37 instant messaging on Linux 142 144 Internet domains looking up registration of 125 J Java language 178 javac program 178 job control in Linux shells 30 32 Index 185 jobs command 30 jobs scheduling 155 159 K KDE graphical environment 2 Fedora Linux and 10 getting help with 8 Konquerer web browser 136 logging out shutting down 11 running shells within 11 xclock command 152 xscreensaver program 162 Kerberos ust kerberos directory 17 telnet command and 129 kill command 32 109 Konquerer web browser for KDE 136 konsole program 11 ksnapshot command 161 L last command 114 less command 44 cat command and 43 lib directory 16 libexec directory 16 linebreaks in shell scripts 166 linking files 40 Linux backing up files 95 101 components of 2 filesystem layout of 13 20 getting help with 7 installing software on the sys
153. ot Alex Schowtka and Robert Dulaney at VistaPrint and my wonderful family Lisa and Sophie FinalWords 179 Symbols recalling previous command 29 slash root directory 13 amp ampersand running background jobs 30 amp amp two ampersands stopping execution of combined commands 27 period current directory 14 two periods parent directory 14 semicolon combine commands using 26 left square bracket alias for test command 168 backward slash escaping special characters 27 Z command suspending jobs 31 pipe operator 26 stopping execution of combined commands 27 tilde denoting home directories 15 23 Index A abiword program 56 absolute path of current directory printing 41 acroread viewer 49 Ada language 178 alias command 25 alphabetical order sorting text in 77 ampersand amp running background jobs 30 apt program 35 arguments for commands 3 aspell command 103 at command 156 157 atq command 157 atrm command 157 attributes of files changing 64 viewing 65 audacity graphical audio file editor 165 audio on Linux systems 163 165 awk filter program 81 vs tr command 77 We d like to hear your suggestions for improving our indexes Send email to index oreilly com 181 background jobs running 30 backing up Linux files 95 101 backquotes on command line 27 backward slash escaping
154. ourself again This is the simplest way to obtain superuser privileges on the system There are other programs for doing so which offer more control such as sudo but they are beyond the scope of this book If you provide a username to su su 1 jones Password KkEkkk you can become that user provided you know her password Useful options 1 Run a login shell You almost always want this option so root s proper search path is set m Preserve your current environment variables in the new shell c command Run just this command as the other user and exit If you need to do this a lot read the sudo manpage s shell Run the given shell e g bin bash Working with Groups groups Print the group membership of a user groupadd Create a new group groupdel Delete a group groupmod Modify a group A group is a set of user accounts treated as a single entity If you give permission for a group to take some action such as modify a file then all members of that group can take it For Working with Groups 119 example you can give full permissions for the group friends to read write and execute the file tmp sample groups users smith friends chgrp friends tmp sample chmod 770 tmp sample ls 1 tmp sample rwxrwx 1 smith friends 2874 Oct 20 22 35 tmp sample To add users to a group edit etc group as root To change the group ownership of a file recall the chgrp commands from
155. ouse Button XTerm Don t confuse the window program like konsole with the shell running inside it The window is just a container albeit with fancy features of its own but the shell is what prompts you for commands and runs them If you re not running a graphical interface say you re log ging in remotely over the network or directly over an attached terminal a shell will run immediately when you log in No shell window is required Logins Logouts and Shutdowns We assume you know how to log into your Linux account To log out from GNOME or KDE click the red hat icon in the Logins Logouts andShutdowns 11 taskbar and choose Logout from the main menu To log out from a remote shell just close the shell type exit or logout Never simply turn off the power to a Linux system it needs a more graceful shutdown To perform a shutdown from GNOME choose Logout gt Shut Down From KDE first log out then on the login screen click the Shutdown icon To perform a shutdown from a shell run the shutdown com mand as the superuser as follows shutdown options time message SysVinit sbin stdin stdout file opt help version The shutdown command halts or reboots a Linux system only the superuser may run it Here s a command to halt the system in 10 minutes broadcasting the message scheduled maintenance to all users logged in shutdown h 10 scheduled maintenance The time may b
156. ps and Remote Storage on page 95 i Immutable file cannot be changed or deleted root only j Journaled data ext3 filesystems only s Secure deletion if deleted this file s data is overwritten with zeroes S Synchronous update changes are written to disk immediately as if you had typed sync after saving see Disks and Filesystems on page 91 u Undeletable file cannot be deleted undeletable 64 Linux Pocket Guide Useful options R Recursively process directories Isattr options files e2fsprogs usr bin stdin stdout file opt help version If you set extended attributes with chattr you can view them with lsattr list attributes The output uses the same letters as chattr for example this file is immutable and undeletable lsattr myfile u i myfile Useful options R Recursively process directories a List all files including those whose names begin with a dot d If listing a directory do not list its contents just the directory itself With no files specified lsattr prints the attributes of all files in the current directory File Location find Locate files in a directory hierarchy slocate Create an index of files and search the index for string which Locate executables in your search path command type Locate executables in your search path bash builtin whereis Locate executables documentation and source files Linux systems can contain tens or hun
157. rd matching a filenames aardvark agnostic apple echo a As a literal asterisk a The Shell 27 echo I live in HOME Dollar sign means a variable value I live in home smith echo I live in HOME A literal dollar sign I live in HOME You can also escape control characters tabs newlines D and so forth to have them used literally on the command line if you precede them with V This is particularly useful for tab I characters which the shell would otherwise use for filename completion see Filename completion on page 29 echo There is a tab between here V Iand here There is a tab between here and here Command line editing bash lets you edit the command line you re working on using keystrokes inspired by the text editors emacs and vi see File Creation and Editing on page 51 To enable command line editing with emacs keys run this command and place it in your bash_profile to make it permanent set o emacs For vi keys set o vi vi keystroke emacs keystroke first type ESC Meaning AP or up arrow k Previous command line AN or down arrow j Next command line AF or right arrow Forward one character AB or left arrow h Backward one character AA 0 Beginning of line AE End of line AD X Delete next character AU AU Erase entire line 28 Linux Pocket Guide Command history You can recall previous commands you ve run that is the shell s history
158. rd options tracks cdrecord usr bin stdin stdout file opt help version The cdrecord command burns a CD R disc on a SCSI CD writer or an IDE CD writer using Linux ide scsi emulation To burn the contents of a directory onto a CD ROM readable on Linux Windows and Macintosh systems 1 Locate your CD writer s device by running cdrecord scanbus 0 0 0 0 0 1 0 1 0 2 0 2 0 3 0 3 YAMAHA CRW6416S 1 0d Removable CD ROM The device in this case is 0 3 0 2 Find out your CD writer s speed for writing CD R or CD RW discs whichever you re using Suppose it is a 6x writer of CD Rs so the speed is 6 Specifically an IS09660 CD with Rock Ridge extensions mkisofs can cre ate other formats for cdrecord to burn see man mkisofs Backups and Remote Storage 99 3 Put the files you want to burn into a directory say dir Arrange them exactly as you d like them on the CD The directory dir itself will not be copied to CD just its contents 4 Burn the CD DEVICE 0 3 0 SPEED 6 mkisofs R l dir gt mydisk iso cdrecord v dev DEVICE speed SPEED mydisk iso or if your system is fast enough you can do this with a single pipeline mkisofs R 1 dir cdrecord v dev DEVICE speed SPEED cdrecord can burn music CDs as well but you might want to use a friendlier graphical program like xcdroast instead see Audio and Video on page 163 which is built on top of
159. rd one screenful Enter search mode Follow it with a regular expression and press Enter and less will look for the first line matching it Same as but it searches backward in the file n Repeat your most recent search forward N Repeat your most recent search backward Although technically less can be plugged into the middle of a pipeline or its output redirected to a file there isn t much point to doing this 44 Linux Pocket Guide Keystroke Meaning v Edit the current file with your default text editor the value of environment variable VISUAL or if not defined EDITOR or if not defined vi lt Jump to beginning of file gt Jump to end of file n Jump to next file p Jump to previous file less has a mind boggling number of features we re presenting only the most common The manpage is recommended reading Useful options C Clear the screen before displaying the next page m Print a more verbose prompt displaying the percentage of the file displayed so far N Prepend line numbers to the output Y Display control characters literally normally Less converts them to a human readable format S Squeeze multiple adjacent blank lines into a single blank line S Truncate long lines to the width of the screen instead of wrapping head options files coreutils usr bin stdin stdout file opt help version The head command prints the first 10 lines of a file great for prev
160. re all text based For a graphical file com parison tool try xxdiff at http xxdiff sourceforge net diff options file1 file2 diffutils usr bin stdin stdout file opt help version The diff command compares two files line by line or two direc tories When comparing text files diff can produce detailed reports of their differences For binary files diff merely reports whether they differ or not For all files if there are no differences diff produces no output The traditional output format looks like this Indication of line numbers and the type of change lt Corresponding section of file1 if any gt Corresponding section of file2 if any 86 Linux Pocket Guide For example if we start with a file fileA Hello this is a wonderful file The quick brown fox jumped over the lazy dogs Goodbye for now Suppose we delete the first line change brown to blue on the second line and add a final line creating a file fileB The quick blue fox jumped over the lazy dogs Goodbye for now Linux roolz Then diff fileA fileB produces this output 1 2c1 fileA lines 1 2 became fileB line 1 lt Hello this is a wonderful file Lines 1 2 of fileA lt The quick brown fox jumped over diff separator gt The quick blue fox jumped over Line 1 of fileB 4a4 Line 4 was added gt Linux roolz The added line The leading symbols lt and gt are arrows indicating fileA and fileB respectiv
161. rectory say mnt mydir mkdir mnt mydir mount dev hda1 mnt mydir df mnt mydir Filesystem 1K blocks Used Available Use Mounted on dev hda1 1011928 285744 674780 30 mnt mydir mount has tons of options and uses we will discuss only the most basic In most common cases mount reads the file etc fstab filesystem table to learn how to mount a desired disk For example if you type mount usr the mount command looks up the usr line in etc fstab which might look like this dev hda8 usY ext3 defaults 1 2 Here mount learns among other things that disk device dev hda8 should be mounted on usr as a Linux ext3 formatted filesystem mount is run typically by the superuser but common devices like floppy and CD ROM drives often can be mounted and unmounted by any user mount mnt cdrom mount mnt floppy umount options device directory mount bin stdin stdout file opt help version umount is the opposite of mount it makes a disk partition unavail able For instance if you ve mounted a CD ROM disc you can t eject it until it s umounted umount mnt cdrom Always unmount removable media before ejecting it or you risk damage to its filesystem To unmount all mounted devices umount a Alternatively you can use the t option of mount to specify the filesystem type directly such as mount t ext3 dev hda1 mnt mydir See man mount Disks and Filesystems
162. rence printf This is a quote s n This is a quote printf This is a quote q n This is a quote It is your responsibility to make sure the number of format specifi cations equals the number of arguments supplied to printf If you have too many arguments the extras are ignored and if you have too few printf assumes default values 0 for numeric formats for string formats Nevertheless you should treat such mismatches as errors even though printf is forgiving If they lurk in your shell scripts they are bugs waiting to happen Format specifications are described in detail on the manpage for the C function printf see man 3 printf Here are some useful ones d Decimal integer ld Long decimal integer o Octal integer x Hexadecimal integer 146 Linux Pocket Guide f Floating point lf Double precision floating point c A single character s String q String with any shell metacharacters escaped A percent sign by itself Just after the leading percent sign you can insert a numeric expression for the minimum width of the output For example 5d means to print a decimal number in a five character wide field and 6 2f means a floating point number in a six char acter wide field with two digits after the decimal point Some useful numeric expressions are n Minimum width n on Minimum width n padded with leading zeroes n m Minimum width n with m digits after th
163. riptions of the signals run man 7 signal nice priority command_line coreutils bin stdin stdout file opt help version When invoking a system intensive program you might want to be nice to the other processes and users by lowering its priority That s what the nice command is for Here s an example of setting a big job to run at priority 7 nice 7 sort VeryLargeFile gt outfile Controlling Processes 109 If you don t specify a priority 10 is used To find out the default priority i e what you d get if you didn t run nice type nice with no arguments nice 0 If you re the superuser you can also raise the priority lower the number nice 10 Yes that s dash negative 10 To see the nice levels of your jobs use ps and look at the NI column ps o pid user args nice renice priority options PID util linux usr bin stdin stdout file opt help version While the nice command can invoke a program at a given priority renice changes the priority of an already running process Here we increase the nice level decrease the priority of process 28734 by five renice 5 p 28734 Ordinary users can decrease priorities increase the number and the superuser can increase priorities decrease the number The valid range is 20 to 20 but avoid highly negative numbers or you might interfere with vital system processes Useful options p pid A
164. ro 09 k Hour 24 hour clock leading blank 9 H Hour 24 hour clock leading zero 09 N Nanoseconds 737418000 s Seconds since the beginning of Linux 1068583983 time midnight January 1 1970 Other n Newline t Tab Percent sign 154 Linux Pocket Guide Through its options date can also display other dates and times Useful options d date_or time string Display thegivendate or time string formatted as you wish r filename Display the last modified timestamp of the given file formatted as you wish s date_or_time_string Setthe system date and or time only the superuser can do this ntpdate timeserver ntp usr sbin stdin stdout file opt help version The ntpdate command sets the current system time by contacting a timeserver machine on the network You must be root to set the system time usr sbin ntpdate timeserver someplace edu 7 Sep 21 01 25 ntpdate 2399 step time server 178 99 1 8 offset 0 51 sec To keep your system date in sync with a timeserver over long periods use the daemon ntpd instead see http www ntp org If you don t know a local timeserver search Google for public ntp time server Scheduling Jobs sleep Wait a set number of seconds doing nothing watch Run a program at set intervals at Schedule a job for a single future time crontab Schedule jobs for many future times If you need to launch programs at particular times or at regu lar intervals Linux provid
165. roup changing its name or group ID groupmod n newname friends groupmod does not affect any files owned by this group it simply changes the ID or name in the system s records Be careful when changing the ID or these files will have their group ownership set to a nonexistent group Useful options g gid Change the group s ID to gid n name Change the group s name to name Basic Host Information uname Print basic system information hostname Print the system s hostname dnsdomainname Same as hostname d domainname Same as hostname y nisdomainname Same as hostname y Basic Host Information 121 ypdomainname Same as hostname y ifconfig Set and display network interface information Every Linux machine or host has a name a network IP address and other properties Here s how to display this information uname options coreutils bin stdin stdout file opt help version The uname command prints fundamental information about your computer uname a Linux server example com 2 4 18 27 8 0 1 Fri Mar 14 06 45 49 EST 2003 1686 i686 i386 GNU Linux This includes the kernel name Linux hostname server example com kernel version 2 4 18 27 8 0 1 Fri Mar 14 06 45 49 EST 2003 hardware name i686 processor type i686 hardware platform i386 and operating system name GNU Linux Useful options a Allinformation S Only the kernel name the default n Only the hostnam
166. s 86 90 completing filenames with TAB key 29 compress command 83 software installation and 34 tar Z command and 99 zip command and 85 compressing uncompressing files 82 85 182 Index conditionals in shell scripts 170 172 configure script running 37 configuring the shell 33 connecting to networks 128 131 continue command 175 controlling processes 108 110 cp command 39 cpio program 96 cron process 158 crontab command 158 159 CUPS printing system 101 curl command 138 curly brace expressions expanding 23 cut command 75 D date command 153 155 watch command and 156 dc desk calculator command 151 default editor setting 52 dev directory 17 df disk free program 92 diff program 86 diff3 program 86 88 dig command 125 directories Linux 13 changing using cd command 41 creating 42 deleting empty directories 42 home directories 14 operating system directories 18 printing absolute path of 41 system directories 15 18 dirname command 42 disk usage command du 59 disks and filesystems 91 95 DISPLAY variable 23 dnsdomainname command 121 doc directory 16 domainname command 121 du disk usage command 59 dump command 96 chattr command and 64 restore command and 97 DVI files 50 dvips command 50 E echo command 7 145 script output provided by 167 ed line editor 81 diff e command 87 EDITOR environment variable 45 setting de
167. s a good idea to surround it with double quotes to prevent cer tain runtime errors An undefined variable or a variable with spaces in its value will evaluate to something unexpected if not surrounded by quotes causing your script to malfunction FILENAME My Document Space in the name ls FILENAME Try to list it 166 Linux Pocket Guide ls My No such file or directory Oops ls saw 2 arguments ls Document No such file or directory 1s 1 FILENAME List it properly My Document Is saw only 1 argument If a variable name is evaluated adjacent to another string sur round it with curly braces to prevent unexpected behavior HAT fedora echo The plural of HAT is HATs The plural of fedora is Oops No variable HATs echo The plural of HAT is HAT s The plural of fedora is fedoras What we wanted Input and Output Script output is provided by the echo and printf commands which we described in Screen Output on page 144 echo Hello world Hello world printf I am d years old n expr 20 20 I am 40 years old Input is provided by the read command which reads one line from standard input and stores it in a variable read name Sandy Smith lt ENTER gt echo I read the name name I read the name Sandy Smith Booleans and Return Codes Before we can describe conditionals and loops we need the concept of a Boolean true false test To the shell the value 0 means tr
168. s it runs Once processes are started they can be stopped restarted killed and reprioritized We discussed some of these opera tions as handled by the shell in Job Control on page 29 Now we cover killing and reprioritizing 108 Linux Pocket Guide kill options process_ids bash shell built in stdin stdout file opt help version The kill command sends a signal to a process This can termi nate a process the default interrupt it suspend it crash it and so on You must own the process or be the superuser to affect it kill 13243 If this does not work some programs catch this signal without terminating add the KILL option kill KILL 13243 which is virtually guaranteed to work However this is not a clean exit for the program which may leave resources allocated or other inconsistencies upon its death If you don t know the PID of a process try the pidof command sbin pidof emacs or run ps and examine the output In addition to the program bin kill in the filesystem most shells have built in kill commands but their syntax and behavior differ However they all support this usage kill N PID kill NAME PID where N is a signal number and NAME is a signal name without its leading SIG e g use HUP to send the SIGHUP signal To see a complete list of signals transmitted by kill run kill 1 though its output differs depending which kill you re running For desc
169. s of packaging files on Linux and Unix systems tar czvf myarchive tar gz mydir Create tar tzvf myarchive tar gz List contents tar xzvf myarchive tar gz Extract If you specify files on the command line only those files are processed tar xvf dev tape file1 file2 file3 Otherwise the entire archive is processed Useful options c Create an archive You ll have to list the input files and directories on the command line Y Append files to an existing archive u Append new changed files to an existing archive A Append one archive e g a tar file to the end of another archive eg tar A f dev tape myfile tar t List the archive X Extract files from the archive 98 Linux Pocket Guide f file Read the archive from or write the archive to the given file This could be a device such as dev tape or a plain file if you want to create a traditional Linux tar file d Diff compare the archive against the filesystem Z Compress while writing or uncompress while reading the data with gzip j Compress while writing or uncompress while reading the data with bzip2 Z Compress while writing or uncompress while reading the data with Unix compress b N Use a block size of N 512 bytes v Verbose mode print extra information h Follow symbolic links 1 Do not cross filesystem boundaries p When extracting files restore their original permissions and ownership cdreco
170. sed with s or f sort will ignore the specified number of characters or fields first then consider the next N characters tee options files coreutils usr bin stdin stdout file opt help version Like the cat command the tee command copies standard input to standard output unaltered Simultaneously however it also copies that same standard input to one or more files tee is most often found in the middle of pipelines writing some intermediate data to a file while also passing it to the next command in the pipeline who tee original_who sort This would print the sorted output of who on standard output but write the original unsorted output of who to the file original_who Useful options a Append instead of overwriting files i Ignore interrupt signals More Powerful Manipulations We ve just touched the tip of the iceberg for Linux text filter ing Linux has hundreds of filters that produce ever more complex manipulations of the data But with great power 80 Linux Pocket Guide comes a great learning curve too much for a short book Here are a few filters to get you started awk awk is a pattern matching language It can match data by reg ular expression and perform actions based on the data Here are a few simple examples for processing a text file myfile Print the second and fourth word on each line awk print 2 4 myfile Print all lines that are shorter than 60 chara
171. slocate r command 69 remote machines logging into with telnet 129 looking up hostnames 124 sending ICMP packets to 126 traceroute command 127 renice command 110 reset command 33 restore command 97 mt command and 96 resuming jobs with fg command 32 return codes of Linux commands 167 178 rm command 39 RMAIL program 132 rmdir command 42 root directory 13 root user 4 118 RPM Red Hat Package Manager files 34 rpm command 34 36 RPM packages commands for manipulating 35 rsync command 100 run directory 17 S sbin directory 16 scalc command 56 scheduling jobs 155 159 scp secure copy command 130 screensavers viewing editing 160 163 xscreensaver program 162 sdiff program 86 88 sdraw command 56 secure copy scp command 130 secure shell ssh program 128 sed filter program 81 vs tr command 77 semicolon combine commands using 26 sendmail program 133 seq command 148 sfax command 56 sfdisk program 95 sftp program 130 share directory 16 shell prompts 3 for superuser commands 4 shell scripts break and continue in 174 command line arguments in 177 conditionals in 170 172 creating 176 exiting with return codes 178 loops in 172 174 programming with 166 178 running 176 SHELL variable 24 188 Index shell windows opening 11 shells 20 33 changing login shell program 118 history related commands 29 job control 30 32 running 11 suspending 31
172. specifically BSD Unix the default or System V Unix s option and cksum produces a CRC checksum sum myfile 12410 3 sum s myfile 47909 6 myfile cksum myfile 1204834076 2863 myfile The first integer is a checksum and the second is a block count But as you can see these checksums are small numbers and there fore unreliable since files could have identical checksums by coincidence md5sum is by far the best 90 Linux Pocket Guide Disks and Filesystems df Display available space on mounted filesystems mount Make a disk partition accessible umount Unmount a disk partition make it inaccessible fsck Check a disk partition for errors sync Flush all disk caches to disk Linux systems can have multiple disks or disk partitions In casual conversation these are variously called disks parti tions filesystems volumes even directories We ll try to be more accurate A disk is a hardware device which may be divided into parti tions that act as independent storage devices Partitions are rep resented on Linux systems as special files in usually the dev directory For example dev hda7 could be a partition on your master IDE disk Some common devices in dev are hda First IDE bus master device partitions are hda 1 hda2 hdb First IDE bus slave device partitions are hdb 1 hdb2 hdc Second IDE bus master device partitions are hdc1 hdc2 hdd Second IDE bus slave device partit
173. ss to display a numeric progress meter while files are copied e command Specify a different remote shell program such as ssh for more security File Printing lpr Print a file Ipq View the print queue Iprm Remove a print job from the queue Linux has two popular printing systems called CUPS and LPRng Fedora comes with CUPS Both systems use com mands with the same names lpr lpg and lprm However these commands have different options depending whether you re using CUPS or LPRng To be generally helpful we will present common options that work with both systems To install a printer for use with Fedora run the command redhat config printer and follow the directions Ipr options files cups usr bin stdin stdout file opt help version The lpr line printer command sends a file to a printer lpr P myprinter myfile File Printing 101 Useful options P printername Send the file to printer printername which you have previously set up with redhat config printer N Print N copies of the file J name Set the job name that prints on the cover page if your system is set up to print cover pages Ipg options cups usr bin stdin stdout file opt help version The 1pq line printer queue command lists all print jobs waiting to be printed Useful options P printername List the queue for printer printername a List the queue for all printers 1 Be verbose
174. sunday at gt echo Remember to go shopping Mail smith at gt lpr HOME shopping list at gt D lt EOT gt job 559 at 2003 09 14 21 30 156 Linux Pocket Guide The time specifications understood by at are enormously flexible In general you can specify e A time followed by a date not a date followed by a time e Only a date assumes the current clock time e Only a time assumes the very next occurrence whether today or tomorrow e A special word like now midnight or teatime 16 00 e Any of the above followed by an offset like 3 days Dates are acceptable in many forms december 25 2003 25 december 2003 december 25 25 december 12 25 2003 25 12 2003 20031225 today thursday next thursday next month next year and more Month names can be abbreviated to three letters jan feb mar Times are also flexible 8pm 8 pm 8 00pm 8 00 pm 20 00 and 2000 are equivalent Offsets are a plus or minus sign followed by whitespace and an amount of time 3 seconds 2 weeks 1 hour and so on If you don t specify a part of the date or time at copies the missing information from the system date and time So next year means one year from right now thursday means the upcoming Thursday at the current clock time december 25 means the next upcoming December 25 and 4 30pm means the very next occurrence of 4 30 p m in the future Your command is not evaluated by the shell unti
175. t variable 45 setting default editor 52 Ww w command 106 watch command 156 wc command 3 58 web browsing 136 140 wget command 138 140 whereis command 70 locating files 66 which command 70 locating files 66 190 Index while loops 172 infinite loops and 174 whitespace programming with shell scripts 166 quoting on command line 27 who command 112 tee command and 80 whoami command 111 whois command 125 wildcard characters and the shell 22 windows shell opening 11 Word documents editing with abiword 56 editing with soffice 55 write program 143 Writer program soffice 56 www directory 16 X X11 directory 17 xargs command 68 xcalc command 149 xcdroast program 100 165 xclock command 152 xdvi command 50 Ximian Evolution program 132 xload command 107 xmms command 164 xpdf viewer 49 xscreensaver program 162 xscreensaver command command 163 xscreensaver demo command 163 xterm program 11 xv program using instead of GIMP 161 xxd command 48 xxdiff program 86 y yes command 147 ypdomainname command 121 yum program 35 Z Z command suspending jobs 31 zcat command 83 zip command 85 Index 191
176. ted HTTP request sent awaiting response 200 OK Length unspecified text html lt gt 31 434 220 84K s 23 19 51 220 84 KB s index html saved 31434 which is saved to a file index html in the current directory wget has the added ability to resume a download if it gets interrupted in the middle say due to a network failure just run wget c with the same URL and it picks up where it left off Another similar command is curl which writes to standard output by default unlike wget which duplicates the original page filenames by default curl http www yahoo com gt mypage html 138 Linux Pocket Guide wget has over 70 options so we ll cover just a few important ones curl has a different set of options see its manpage Useful options i filename 0 filename t N progress dot progress bar spider nd A pattern1 pattern2 pattern3 R pattern1 pattern2 pattern3 Read URLs from the given file and retrieve them in turn Write all the captured HTML to the given file one page appended after the other Continue mode if a previous retrieval was interrupted leaving only a partial file as a result pick up where wget left off That is if wget had downloaded 100K of a 150K file the c option says to retrieve only the remaining 50K and append it to the existing file wget can be fooled however if the remote file has changed since the first partial download s
177. tem 33 37 spell checkers in 103 104 In command 40 lock directory 17 log directory 17 ogname command 111 LOGNAME variable 24 ogout command 12 ook command 103 oops in shell scripts 172 174 lost found directory 18 pq line printer queue command 102 pr line printer command 101 prm line printer remove command 102 LPRng printing system 101 s command 6 38 displaying file properties 57 file protections and 19 sattr list attributes command 65 ynx command 136 138 M m4 macro processing language 81 magnetic tape command mt 96 mail directory 17 mail program 135 mail readers 132 135 MAIL variable 24 mailq command 132 make command 37 make install command 37 man command 8 16 man directory 16 masks and protection modes 55 math commands 149 152 md5sum program 86 90 memory usage displaying 108 mesg program 113 144 Microsoft Excel documents editing with abiword 56 editing with soffice 55 186 Index Microsoft Word documents editing with abiword 56 editing with soffice 55 misc directory 17 mkdir command 42 mkfs program 95 mkisofs command 99 mnt directory 17 mount command 93 Mozilla web browser 136 reading email 132 reading Usenet news 140 mplayer video player 163 mt magnetic tape command 96 mutt mailer 133 135 mv command 39 N Netscape web browser 136 network connections establishing 128 131 network interface displ
178. ter them in the original shell 176 Linux Pocket Guide shell setting variables changing directory and so on it 0 can be run in the current shell with the command myscript Command Line Arguments Shell scripts can accept command line arguments and options just like other Linux commands In fact some com mon Linux commands are scripts Within your shell script you can refer to these arguments as 1 2 3 and so on cat myscript bin bash echo My name is 1 and I come from 2 myscript Johnson Wisconsin My name is Johnson and I come from Wisconsin myscript Bob My name is Bob and I come from Your script can test the number of arguments it received with if lt 2 then echo 0 error you must supply two arguments else echo My name is 1 and I come from 2 fi The special value 0 contains the name of the script and is handy for usage and error messages myscript Bob myscript error you must supply two arguments To iterate over all command line arguments use a for loop with the special variable which holds all arguments for arg in do echo I found the argument arg done Programming with Shell Scripts 177 Exiting with a Return Code The exit command terminates your script and passes a given return code to the shell By tradition scripts should return 0 for success and 1 or other nonzero value on failure If your script do
179. terminating 33 vs programs 21 see also bash shutdown command 12 simpress command 56 slabel command 56 slash root directory 13 sleep command 156 slocate secure locate command 69 locating files 66 slrn newsreader 140 142 smpeg video player 163 soffice program 55 sort command 77 special characters escaping 27 spell checkers in Linux 103 104 spell command 104 spool directory 17 src directory 16 ssh secure shell program 128 standard output printing messages on 144 149 stat command 57 su command 5 becoming superuser 118 software installation and 34 whoami command and 111 subdirectories Linux 13 sudo program 119 sum program 86 90 superusers 4 becoming 118 suspend command 31 swriter command 56 symbolic links 40 sync command 64 94 system directories 15 18 system load displaying graphically 107 T t3d clock program 152 TAB key completing filenames with 29 tailcommand 46 talk program 143 tape drives copying files to 96 tar command 98 mt command and 96 software installation and 34 tar files 36 compressed sample commands 84 85 gzipped sample commands 83 tee command 80 telnet program 129 TERM variable 24 terminating shells 33 test command 168 169 text manipulation commands 71 80 tilde denoting home directories 15 23 time displaying setting 152 155 timestamps changing 60 tmp directory 17 top command 106 touch command 60
180. the p option the plain hexdump format If you re bored try either of these commands to convert and unconvert a file in a pipeline reproducing the original file on standard output xxd myfile xxd r xxd p myfile xxd r p gv options file gv ust X11R6 bin stdin stdout file opt help version GhostView displays an Adobe Postscript or PDF file in an X window You can invoke it as gv or ghostview The basic opera tion of the program is simple click the desired page number to jump to that page and so forth A few minutes of playing time and you ll have the hang of it GhostView is the definitive Linux Postscript viewer but other free PDF viewers include acroread http www adobe com and xpdf http www foolabs com xpdf FileViewing 49 Useful options page P Begin on page P Default 1 monochrome Use the given display mode grayscale color portrait Choose the page orientation which normally gv determines landscape automatically seascape upsidedown scale N Set the scaling factor i e the zoom for the display The integer N may be positive make the image larger or negative smaller watch Automatically reload the Postscript file or don t when it changes nowatch xdvi options file tetex xdvi usr bin stdin stdout file opt help version The document processing system TeX produces binary output files in a format called DVI with suffix dvi The viewer xdvi
181. they just indicate their contents are optional and words in italics mean you have to fill in your own specific values like names of actual files If you see a vertical bar between options or arguments perhaps grouped by parentheses ls file directory this indicates choice when running the 1s command you may supply either a file or directory name as an argument Input and output Most Linux programs accept data from standard input which is usually your keyboard and produce output on standard output which is usually your screen Additionally error mes sages are usually displayed on standard error which also is usually your screen but kept separate from standard output Later we ll see how to redirect standard input output and error to and from files or pipes But let s get our vocabulary straight When we say a command reads we mean from For example you can capture standard output in a file and still have stan dard error messages appear on screen What s in This Book 5 standard input unless we say otherwise And when a com mand prints we mean on standard output unless we re talking about computer printers Standard heading Each command description begins with a heading like this one for the 1s list files command Is options files coreutils bin stdin stdout file opt help version The heading includes the command name 1s and usage the directory in which it is lo
182. to a remote host or run commands on it telnet Log into a remote host insecure scp Securely copy files to from a remote host batch sftp Securely copy files to from a remote host interactive ftp Copy files to from a remote host interactive insecure With Linux it s easy to establish network connections from one machine to another for remote logins and file transfers Just make sure you do it securely ssh options host command openssh clients usr bin stdin stdout file opt help version The ssh Secure Shell program securely logs you into a remote machine where you already have an account ssh remote example com Alternatively it can invoke a program on that remote machine without logging you in ssh remote example com who ssh encrypts all data that travels across its connection including your username and password which yow ll need to access the remote machine The SSH protocol also supports other ways to authenticate such as public keys and host IDs See man sshd for details 128 Linux Pocket Guide Useful options l username Specify your remote username otherwise ssh assumes your local username You can also use the syntax username host ssh smith server example com p port Use a port number other than the default 22 t Allocate a tty on the remote system useful when trying to run a remote command with an interactive user interface such as a text editor v Produce ver
183. trol the program s behavior xscreensaver command activate Blank now xscreensaver command next Choose next animation xscreensaver command prev Choose previous animation xscreensaver command cycle Choose random animation xscreensaver command lock Lock the screen now xscreensaver command exit Quit Audio and Video grip CD player ripper and MP3 encoder xmms Audio file player MP3 WAV cdparanoia Rip audio from CDs to WAV files audacity Edit audio files xcdroast CD burner with graphical interface Audio is alive and well on Linux systems Most of the pro grams we ll cover have intuitive user interfaces tons of fea tures and reasonable documentation so we won t discuss them in detail Mainly we want you to have a taste of what s available and possible Some comprehensive web sites devoted to Linux audio and MIDI are http inux sound org and http www xdt com ar inux snd Fedora does not include any video players but you can download and install them Some popular ones are smpeg http www lokigames com development and mplayer http www mplayerhq hu grip options grip usr bin stdin stdout file opt help version grip is a CD player and an audio ripper it can play CDs extract audio from CDs save it in WAV files and convert the files to MP3s It has extensive built in help and fairly intuitive controls Audio and Video 163 cdparanoia options span outfile cdpara
184. ue or success and anything else means false or failure Additionally every Linux command returns an integer value called a return code or exit status to the shell when the com mand exits You can see this value in the special variable cat myfile My name is Sandy Smith and Programming with Shell Scripts 167 I really like Fedora Linux grep Smith myfile My name is Sandy Smith and A match was found echo 0 so return code is success grep aardvark myfile echo No match was found 1 so return code is failure The return codes of a command are usually documented on its manpage test and The test command built into the shell will evaluate simple Boolean expressions involving numbers and strings setting its exit status to 0 true or 1 false 4 test 10 lt 5 Is 10 less than 5 echo 1 No it isn t test n hello Does the string hello have nonzero length echo 0 Yes it does A list of common test arguments are found in Table 12 for checking properties of integers strings and files test has an unusual alias left square bracket as a shorthand for use with conditionals and loops If you use this shorthand you must supply a final argument of right square bracket to signify the end of the test The following tests are identical to those before 10 It 5 echo 1 n hello echo 0 Remember
185. us on Bash the Bourne Again Shell located in bin bash which is the Fedora Linux default The Shell Versus Programs When you run a command it might invoke a Linux program like who or instead it might be a built in command a fea ture of the shell itself You can tell the difference with the type command type who who is usr bin who type cd cd is a shell builtin It is helpful to know what the shell provides versus what Linux does The next few sections describe features of the shell Selected bash Features A shell does much more than simply run commands It also provides powerful features to make this task easier Examples Actually how many interactive shells those users are running If a user has several shells running like the user silver in our example they ll have that many lines of output in who The Shell 21 are wildcards for matching filenames redirection of com mand output and input to and from files pipes for making the output of one command become the input of another aliases to run common commands quickly variables for stor ing values for use by the shell and more We re just scratch ing the surface to introduce you to a set of useful tools Run info bash for full documentation Wildcards Wildcards provide a shorthand for specifying sets of files with similar names For example a means all files whose names begin with lowercase a Wildcards are expanded by
186. version number and exit Standard symbols Throughout the book we use certain symbols to indicate keystrokes Like many other Linux documents we use the symbol to mean press and hold the control Ctrl key so for example D pronounced control D means press and hold the control key and type D We also write ESC to mean press the Escape key Keys like Enter and Spacebar should be self explanatory Your friend the echo command In many of our examples we ll print information to the screen with the echo command which we ll formally describe in Screen Output on page 144 echo is one of the simplest commands it merely prints its arguments on standard out put once those arguments have been processed by the shell echo My dog has fleas My dog has fleas echo My name shell is USER Shell variable USER My name is smith Getting Help If you need more information than this book provides there are several things you can do GettingHelp 7 Run the man command The man command displays an online manual page or manpage for a given program For example to get docu mentation on listing files with 1s run man 1s To search for manpages by keyword for a particular topic use the k option followed by the keyword man k database Run the info command The info command is an extended hypertext help sys tem covering many Linux programs info ls If no documentation is found on a
187. view any outgoing mail messages still queued on your machine waiting to be sent evolution evolution usr bin stdin stdout file opt help version Ximian Evolution is a graphical email program that looks a lot like Microsoft Outlook Depending on how your system is set up you can invoke Evolution from the main menu as Internet Evolution Email or by running the command evolution from the shell To set up a mail account 1 Choose Tools gt Settings 2 In the Evolution Settings window if you do not already have an email account listed choose Add Otherwise select the account and choose Edit 3 In the Evolution Account Editor window the Identity tab fill in your full name and email address 4 Choose the Receiving Mail tab and the Server Type IMAP POP local delivery and so on and fill in the fields relevant to your mail server For POP or IMAP servers fill in the mail server host and username supplied by your ISP for local delivery fill in the path to your local mailbox 5 Choose the Sending Mail tab and select the type of your out going mail server SMTP if the server is remote you ll be 132 Linux Pocket Guide prompted for the hostname or sendmail if the server is the local machine 6 The rest of the tabs and options are at your discretion Choose OK to exit the Evolution Account Editor You should be ready for basic mail operations Inbox View your mail New Compose a new mail messa
188. w So if you are displaying a very long file say with the cat command and want to stop type C cat bigfile This is a very long file with many lines Blah blah blah blah blah blah blahblahblah C To kill a program running in the background you can bring it into the foreground with fg and then type C or alterna tively use the kill command see Controlling Processes on page 108 In general C is not a friendly way to end a program If the program has its own way to exit use that when possible You see C kills the program immediately not giving it any chance to clean up after itself Killing a foreground program may leave your shell in an odd or unresponsive state per haps not displaying the keystrokes you type If this happens 32 Linux Pocket Guide 1 Press J to get a shell prompt This produces the same character as the Enter key a newline but will work even if Enter does not 2 Type the word reset even if the letters don t appear while you type and press J again to run this command This should reset your shell C works only when typed into a shell It will likely have no effect if typed in a window that is not a shell window Addi tionally some programs are written to catch the C and ignore it an example is the text editor emacs Terminating a Shell To terminate a shell either run the exit command or type AD exit Tailoring Shell Behavior To configure all your
189. working directory within the dump Add files or directories to the extraction list the list of files you ll want to restore With no arguments add adds the current directory and all its files Add the file filename to the extraction list Add the directory dir to the extraction list The opposite of add remove files from the extraction list If run with no arguments delete removes the current directory and its contents from the extraction list Remove the file my file from the extraction list Remove the directory dir from the extraction list Restore all the files you added to the extraction list Tip if your backup spans multiple tapes start with the last tape and work backwards Backups and Remote Storage 97 restore also works in other noninteractive modes restore x Restore everything from the tape into an existing filesystem cd into the root of the desired filesystem first restore r Restore everything from the tape into a freshly formatted disk partition cd into the root of the desired filesystem first restore t List the contents of the dump restore C Compare the dump against the original filesystem tar options files tar bin stdin stdout file opt help version The tar tape archive program does more than read and write files to and from a tape drive tar cf dev tape myfile1 myfile2 it also lets you create and extract from tar files which are a stan dard mean
190. y choosing an output filename with an appro priate standard extension jpg to produce a JPEG file bmp for a Windows bitmap pbm for a portable bitmap eps for encapsu lated Postscript ico for a Windows icon and so forth For a list of supported file formats click the Save Snapshot button and view the selections under Filter For more information click the Help button in the ksnapshot window or run ksnapshot help all from the shell gimp options files gimp usr bin stdin stdout file opt help version The GIMP GNU Image Manipulation Program is a full featured image editing package that rivals Adobe Photoshop in power and scope It is fairly complex to use but the results can be stunning Visit http www gimp org for full information To run the program type gimp To edit a particular file type gimp filename If the GIMP is more complicated than you need download the xv program for simpler edits from http www trilon com xv Simply display the graphics file xv myfile jpg Graphics and Screensavers 161 and click the right mouse button on the image A menu of editing tools appears gnuplot options files gnuplot usr bin stdin stdout file opt help version The gnuplot program creates graphs plotting points and connecting them with lines and curves and saves them in a wide variety of printer and plotter formats such as Postscript To use gnuplot you need to learn
191. ystem load in an X window It graphs processor load Y axis over time X axis Useful options update N Update the display every N seconds default 10 scale N Divide the Y axis into N sections default 1 xLoad may add more divisions as the load goes up N is the minimum visible at any time hl color Use this color for the scale divider lines label X Print the text X above the graph default your hostname nolabel Don t print any text label above the graph jumpscroll N When the graph reaches the right margin scroll N pixels to the left and keep drawing default is half the window width Viewing Processes 107 free options procps usr bin stdin stdout file opt help version The free command displays memory usage in kilobytes free total used free shared buffers cached Mem 523812 491944 31868 0 67856 199276 buffers cache 224812 299000 Swap 530104 0 530104 The Linux kernel reserves as much memory as possible for caching purposes so your best estimate of free RAM in the preceding output is 299000 Useful options s N Run continuously and update the display every N seconds b Display amounts in bytes or megabytes respectively m t Add a totals line at the bottom 0 Don t display the buffers cache line Controlling Processes kill Terminate a process or send it a signal nice Invoke a program at a particular priority renice Change a process s priority a

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