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1. spowers server _ Sometimes when the clock hits Web site showing off the best ones 3 00am and you ve been in the server room since 9 o clock the cowsay Install this program and previous day you start to get a little the cow will say whatever you ask batty That s the only explanation it to Bonus there s a GUI version have for programs like cowsay In of cowsay too called xcowsay Linux Still I m glad they re there because life wouldn t be nearly as sl this is a program like to install fun without them Here s a quick list because it makes fun of you when of silly Linux programs off the top of you accidentally type s1 instead my head l d love to hear about more of 1s a steam locomotive chugs SO please send me your crazy Linux across the screen It also shows up Easter eggs and l Il follow up on the if you press caps lock and type LS 20 OCTOBER 2014 WWW LINUXJOURNAL COM t UPFRONT E cmatrix blue pill or red pill marshmallows because you can this little program will suck you watch the entire Star Wars movie in to the Matrix either way in a terminal window Leaving this matrix just requires a Ctrl C thankfully Most of these silly things have been around for years and years but E ibaa bin install this package every so often learn of one never and then type aafire to stoke knew about before Send me your up the ASCII flame Grab your favorites and l Il be sure you get digit
2. to it successfully Once you have made sure everything is working correctly you can set up Gpredict to talk to your hardware This is handled in the interfaces section of the preferences window There are two tabs one for radios and one for rotators Since hamlib communicates over network protocols the radio or rotator doesn t even need to be connected to the same machine You can define one of these pieces of hardware with a hostname a port and the communication details Once you have the hardware configured you can control it by LINUX JOURNAL iPad iPhone Available on the E App Store linuxjournal com ios pulling up the radio control window which you access by clicking the down arrow in the map view and selecting Radio Control Figure 6 You can see the details of the downlink and uplink as well as information about targets Now that you know how to get satellite information for what is moving above your head you should be able to go outside and do some actual observations and see all of the man made objects travelling around It can be inspiring to see how much we already do in space and how much more we could be doing JOEY BERNARD oaoa aR er MPD oT Arduino Trim Slice vDSO A s gt FACRK THIS aA ENet S50 T LDAN L A HOME ROUTE RA LOW VER SERVER H THE ADD A CUSTOM vDSO T A LINUX KERNEL Ip a Music Bm That Get Started Create a Unified ws You Around Pr
3. 48 393847667 Longitude 4 505373167 altitude 30 2 sog 0 062 cog 184 8 ept 0 005 mode 3 GPS time u 2014 07 24T08 53 57 000Z Latitude 48 393847333 lLongitude 4 505373167 altitude 30 2 sog 0 036 cog 189 77 ept 0 005 mode 3 GPS time u 2014 07 247T08 53 58 000Z Latitude 48 393847167 Longitude 4 505373 altitude 30 1 sog 0 041 cog 175 46 ept 0 005 mode 3 Again we use a generator For each iteration the GPSd_client class opens a session with GPSd listens WWW LINUXJOURNAL COM OCTOBER 2014 105 FEATURE Accessing the I O Ports of the BeagleBone Black with Python for a report with position and time information closes the session and returns a namedtuple with the information we wanted NTPd One of these GPSd clients is NTP NTPd processes the NMEA GPS timing sentences to set the date and uses the PPS signal to be more accurate The handling of the PPS signal is available only in the development versions of NTPd not the version in the Debian repositories The version we installed is ntp dev 4 2 70416 Grab it and compile it like this apt get install libcap dev wget http www eecis udel edu ntp ntp spool ntp4 ntp dev ntp dev 4 2 p416 tar gz tar xf ntp dev 4 2 p416 tar gz cd ntp dev 4 2 p416 configure enable all clocks enable Linuxcaps make Modify the etc ntp conf file for the connection to GPSd and the PPS signal listening Server from share
4. 84 OCTOBER 2014 WWW LINUXJOURNAL COM accessible only through a network connection chose to configure them with the bare minimum from the eLinux version There is no X session no fancy Web interface just the good old command line via SSH and the applications are launched automatically at boot via etc rc local They are used in a Unmanned Surtace Vehicle USV and the interactions with the operator are done through a hardware control panel via a serial line through Web interfaces and with networked applications The interactions with the hardware of the USV are done through its many I O ports of course Why Python Do really need to tell you Okay we have enough processing power so Python equals less code and more readability of the applications and a lot of useful modules already are available All code and examples in this article are for Python 2 7 but it would be not very difficult to port it to Python 3 4 Important Usage Precautions You need to take several precautions when working the expansion headers to prevent damage to the board All voltage levels are 3 3V max Application of 5V to any I O pin will damage the processor and void the warranty Analog in voltages are 1 8V max Application of gt 1 8V to any A D pin will damage the processor and void the warranty Do not apply any voltages to any I O pins when the board is not powered on Do not drive any external signals into th
5. Server platform what can be controlled E Windows E OS X E Linux Beta Ubuntu Debian for now Client platforms what can be used to control the systems above E Windows m OS X mM Linux Android E iOS coming soon supposedly Permissions on the demon can be customized for controlling your own computer remotely no local permission required or for allowing other people in to assist you The latter is preferred to avoid anyone barging in on your work session The d mon is available for Windows and OS X and recently they released a beta version of the demon for Ubuntu Debian Linux Thanks to its wonderful cross platform approach and smooth functionality in our testing Chrome Remote Desktop earns this month s Editors Choice award Check it out today at https chrome google com remotedesktop SHAWN POWERS LINUX JOURNAL Android Download the app now in the Android Marketplace d WEB DEVELDPMENT Ns Aed Apps with G e me atalyst gt P Puf r AEN we wt A ee T PEN SOURCE CLASSROOM www linuxjournal com android WWW LINUXJOURNAL COM OCTOBER 2014 31 COLUMNS AT THE FORGE 2014 Book Roundup REUVEN M LERNER Reuven gives his annual rundown of great books on programming languages databases and analytics freelancing and more As I write these words the end of summer is approaching and with it so is the time for my annual book roun
6. a dream interpretation program as a shell script well sort of A reader wrote a letter to me oh happy day and although I m still not entirely sure what she s trying to accomplish it s an interesting puzzle to try to tackle anyway Here s what she asked do not know how to code but have a project in mind that is something like Mad Libs but is for dream interpretation would like for people to be able to type a dream and then the computer program would pick out the nouns and ask the participants to freely associate anything that comes to mind if they were that object or person Then the computer would replace the typed responses back into the typed text for the surreal interpretation Do you think this would be difficult to create Mad Libs tor dreams That s certainly a curious idea particularly given how seemingly random and 38 OCTOBER 2014 WWW LINUXJOURNAL COM disconnected the elements of a dream often seem Dreams have been seen as both visions from the gods and the playground of our subconscious and its need to resolve our daily experiences And then there s Freud who Is pretty sure that if you aren t literally dreaming of cigars it s because you re envious of people with cigars or because you re fixated on cigars but suppressing your interests OOohhhhkay then No cigars okay And no Lewinsky jokes either What we need to accomplish this task is a script that parses input i
7. are some inaccuracies We need to Read AINO from Python To read record a table of corresponding values a temperature sensor wired on AINO between the MCP4725 and AINO in this giving 1mV for 0 1 C we use the MCP4725 To MCU MASTER 10 yF T uF T Figure 9 Bipolar Operation Circuit 102 OCTOBER 2014 WWW LINUXJOURNAL COM BBB_AIN class from the bbb_ain py file see my GitHub page Import time from bbb ain import BBB AIN tempe BBB AIN O valeurmax 180 for value in tempe print 4f value time sleep 0 5 Once again we use a generator At each iteration we read a value on the AIN There is no interrupt mechanism on the AIN we read at the frequency of the tor loop that s why we have to pause at each iteration The only catch is the error Resource Temporarily unavailable error 11 which may occur occasionally How We Use It To pilot our propellers we need to output a voltage between 10 V and 10 V We use two MCP4725s on I2c_1 one with AO on V SS 0x60 and the other with AO on V DD 0x61 We use a bipolar operation type circuit to output 10V 10V from the MCP4725 s 0 3 3V output Figure 9 The MCP4725 outputs are re injected into AINO and AIN1 in order to improve the control loop accuracy And we read the speed of the propellers back WWW LINUXJOURNAL COM OCTOBER 2014 103 with two Trequency voltage converters which we feed to AIN2 and AIN3 Figure 10 T
8. m _ eee ON THE COVER e Network Security and SSH What You Need to Know p 46 e How To Sump Pump Monitor with Raspberry Pi and Python p 56 Sera P i t ist e An Indepth Look at the U Boot Environment Anatomy p 68 e Interview with the Creators of the Hello World Program p 110 e Advanced Vim Macro Techniques p 42 e Use the BeagleBone Black to Command Your Electronic Gear p 82 LINUX JOURNAL ISSN 1075 3583 is published monthly by Belltown Media Inc 2121 Sage Road Ste 395 Houston TX 77056 USA Subscription rate is 29 50 year Subscriptions start with the next issue WWW LINUXJOURNAL COM OCTOBER 2014 5 JOURNAL Subscribe to Linux Journal Digital Edition for only 2 45 an issue Mabe UDI U Ane JOURNAL DEVELOP Gils 1 O14 Design MULTIPLAIFORM OCVELOPMENT ENJOY Timely delivery Off line reading Easy navigation Phrase search and highlighting Ability to save clip and share articles Embedded videos Android amp iOS apps desktop and e Reader versions SUBSCRIBE TODAY Executive Editor Senior Editor Associate Editor Art Director Products Editor Editor Emeritus Technical Editor Senior Columnist Security Editor Hack Editor Virtual Editor JOURNAL Jill Franklin jill linuxjournal com Doc Searls doc linuxjournal com Shawn Powers shawn linuxjournal com Garrick Antikajian garrick linuxjournal com James Gray newproducts linuxjournal com D
9. which should go up in September http igg me at hello world EOF DS Good That s just in advance of this issue of the magazine Any other projects JN We re launching a new segment Superusers The Legendary GNU Linux Show https www youtube com watch v DQbODhkyA4g amp feature youtu be DS Excellent I like Aramis the Gnu and Adalie the penguin JN We re also launching a crowdfunding campaign on Indiegogo that should be up by the time you read this DS Where can readers follow you JN Find us at http www dototot com and on Twitter at https twitter com dotototdotcom or https twitter com helloworldshow m Doc Searls is Senior Editor of Linux Journal He is also a fellow with the Berkman Center for Internet and Society at Harvard University and the Center for Information Technology and Society at UC Santa Barbara PEE Send comments or feedback via http www linuxjournal com contact or to ljeditor linuxjournal com WWW LINUXJOURNAL COM OCTOBER 2014 115
10. 101 44 Range 6245 km El 24 84 Rate 6 203 km s LO 0 MHz Doppler 3018 Hz t UPFRONT Uplink i i A A A A A i 145 890 000 Hz T TF F F F F TY F F F LO 0 MHz Radio 145 890 000 Hz Settings 1 Device test i Engage 2 Device None Cycle 1000 msec AOS in 01 16 15 Figure 6 You can control radios and antenna rotators that are defined in Gpredict The modules section lets you change configuration options used in the display of the Gpredict modules You can change things like the refresh rate for the displays or what map to use as the background for the map view You also can select what type of layout you want for a particular module When you select a new layout you will see a preview of what it will look like in the preferences window There are nine different pre generated layouts available or you can create a custom layout When you select the custom layout you define what it will look like by entering the layout code See the user manual for details on how to define a code to create the layout you want Gpredict also has the ability to control radios and rotators The key to this is the hamlib library By using this library Gpredict can handle Doppler tuning of radios and tracking of antenna rotators When you want to connect hardware to your computer you should verify that hamlib can talk WWW LINUXJOURNAL COM OCTOBER 2014 27 t UPFRONT
11. Otherwise U Boot imports the default compiled in environment to this hashtable Figure 4 shows how the user environment is imported in to the hashtable whereas U Boot along with its default environment relocates to top of the RAM If the user environment Is corrupt or inaccessible U Boot would import the default environment in to the hashtable The use of the RAM resident data structure hashtable is important for various reasons on different variables while still keeping the persistent storage form E t boosts performance as you are simple a linear list manipulating variables in RAM and not in Flash Once the environment has relocated to RAM into the hashtable all E You have to manipulate data only commands operating on environment in RAM and need not access some variables will be working only on this slow Flash driver and deal with the hashtable U Boot does not touch associated complexity the environment variables stored in the persistent storage at all unless it E t allows U Boot to deploy type needs to save the env checks and access control attributes Each environment variable entry User Supplied environment in flash U Boot Binary RAM resident Hashtable U Boot Relocates to top of DDR Environment imported in to Hashtable Binary Figure 4 The user environment is imported into a hashtable If the user environment is corrupt the default environment is imported instead WWW LIN
12. Play or iTunes please send me your transaction ID e mail address and full mailing address we use that to encrypt the files to gm linuxjournal com Once I have that can add you to our subscription database as well The best deal I have for Linux Journal directly is https www pubservice com Subnew2page aspx PC LU amp PK M48RENN I hope that helps Sorry that it s more complicated than we would like but once iTunes and Android closed their subscription environments it became impossible to extract those orders and automatically add them to our database so readers can receive every format we have Mark Irgang Publisher LETTERS Leap Years in Bash or Anywhere Regarding the detection of leap years in Dave Taylor s recent articles there is a very simple way to determine whether a year is a leap year if it s divisible by 4 and not 100 So a simple modulus function will suffice YEAR date Y if S YEAR 4 eq amp S YEAR 100 ne then echo Leap else echo No Leap ri For the real geek during a century an integer binary number can be ANDed with 0x03 and the result is represented by the modulus of 4 If 0 the leap year Jacques Amar Dave Taylor replies There are lots of ways to calculate it for sure like my latest just type date d 12 31 YEAR j and see if it s 365 or 366 Counting Days Dave Taylor s Work the Shell column is one
13. SAMUEL BUCQUET 82 OCTOBER 2014 WWW LINUXJOURNAL COM he BeagleBone Black BBB is a low cost low power credit card size 3 4 x 2 1 board with a lot of features and it costs about 60 It sports a 1GHz Sitara AM335x ARM Cortex A8 an ARMv7 processor from Texas Instruments 512MB of RAM and it has all the I O capabilities you d expect from a typical microcontroller such as access to a CAN bus SPI interface and i2c analog input PWM and so on But the board also holds two PRUs an HDMI video output an SD card slot and 100Mb Ethernet This makes the board a complete ARM PC fully compatible with Linux As icing on the cake Beagle fancies an open hardware philosophy all of the chips and designs are available to the public Right out of the box you can use it for the following m A great learning platform with easy access to the connected hardware You can play with almost all the functionalities from the Web interface with the Bonescript language Just plug in the board via the USB client on a PC open the page of the board http 192 168 7 2 and voila See http beagleboard org getting started e f lt 8 66 57 Om A j P aau oe sccviy KANNAN ELLe 22 IES SMP n gt ASI A AD AR 4 ah AA OM A Sh Ae 4 Lh She She Ae Me Mh _ Lh Ah ihe Th th Lh MH Sh Ah Mh Sh Sh Lh Mh She Lh Li F w w art at oe gt IJE DOO OTO B i 3 wA e ria cr el fttt
14. Using dev interface to clock Last drift adjustment done at 1406096765 seconds after 1969 Last calibration done at 1406096765 seconds after 1969 Hardware clock is on UTC time Assuming hardware clock is kept in UTC time Waiting for clock tick got clock tick Time read from Hardware Clock 2014 07 23 15 42 51 Hw clock time 2014 07 23 15 42 51 1406130171 seconds since 1969 Wed Jul 23 17 42 51 2014 0 438131 seconds To benefit from the new RTC permanently as soon as the system boots modify the etc init d hwclock sh file with this little dirty hack Add to the end of the file echo ds1307 0x68 gt sys class i2c adapter i2c 1 new device HCTOSYS DEVICE rtcl hwclocksh Danger had to comment the udev part of the file and I m still trying to figure how to do that part in a cleaner way if d run udev d dev udev then return 0 fi If Something Goes Wrong with a Component on i2c If the kernel can t see the ds130 7 for example try to detect it on the i2c bus with this i2cdetect y r 1 Oo 1 2 3 4 5 6 7 8 9 abcdef 00 Sak Ge re er Gee ee o Ea Se Be Ger ce 10 pes ae py ees gene eee ie ees Se es ee ete eee ee ces fc 20 30 eee ee ee a ees os Se ES Se Re ee ee eee ee BE Se eee ea eee Ge He ee oe 5Q UU UU UU UU GOl 26 em on Ge 2 26 es 62168 oc oe oe oe
15. You also can use your ISP s SMTP server or Google s Gmail SMTP server If you are using a Gmail account The key Python module used to communicate between the Pi and the A 30500002 You have mail from raspi sump linuxnorth org Please reply with Read to read your message read Raspi Sump Sump Pump Alert Critical The sump pit water level is 35 5 cm Figure 5 SMS Alert sensor is called RP GPIO This module can be used to control so many different types of equipment with your Pi Without delving into the nuts and bolts of RP1 GPIO the module helps you take control of the pins by turning them on and off This allows you to WWW LINUXJOURNAL COM OCTOBER 2014 63 pi raspberrypiz raspi sump csv E m m in Pa ick 1 Co Pa J Hr mi mE a r E m T j F F G i n tal fal P I Pa Pi Figure 6 CSV File Being Updated in Real Time by raspisump py control all sorts of equipment like sensors and LEDs for example You can view the GPIO code in the raspisump py script within the water_level function Similar code is used by many other projects that communicate with the Pi s GPIO pins Adam Lappin s Byte Creation Blog has a good example that helped me learn how to use the RP GPIO module in this project see Resources Raspi Sump is started automatically on bootup of the Raspberry Pi by adding this line to etc rc local right before the last line exit 0 home pi ra
16. You can WWW LINUXJOURNAL COM OCTOBER 2014 25 t UPFRONT Show local time instead of UTC Time format Ymd SH SbMi 505 Number Formats Ground Stations TLE Upda te Message SS Logs 2014 08 06 03 22 41 Reset _ Use Imperial units instead of Metric Interfaces Predict _ Use N SVE W for geographical coordinates Figure 5 The preferences window lets you change all sorts of options update them either from the network or from a local file The default contiguration Is set up to remind you when the TLE data is likely out of date You then can go ahead and update this data For an update over the network the default configuration is to download NORAD data from http www celestrak com For a tutorial on the format for TLE 26 OCTOBER 2014 WWW LINUXJOURNAL COM data visit http www amsat org amsat new tools keps_tutorial php All the other configuration options are available under the menu item Edit gt Preferences Figure 5 Here you can change options like the number formats used or the geographical coordinates There also is a tab for ground stations where you can edit or add ground stations x Gpredict Radio Control test1 Downlink i i i kh A A A Kk 1453 890 000 Hz T F F F T F F T FTF F Doppler 3018 Hz Radio 145 890 000 Hz Target H A ISS Track Mode V V AFSK Packet er J L Ag
17. l m enjoying Howard French s book China s Second Continent How a Million Migrants AT THE FORGE Are Building a New Empire in Africa which describes the experiences and interactions of Chinese expatriates in various African countries Finally as someone who recently finished a PhD can recommend a funny if rather cynical book Surviving Your Stupid Stupid Decision to Go to Grad School by Adam Ruben Perhaps it s easier to laugh at his jokes now that I ve completed the degree but found it not only funny but also therapeutic to know that others had experienced similar problems and challenges to mine during their grad school careers hope these recommendations will provide you with many hours of insightful and interesting reading I m sure have missed many good books that came out in the past year I m always open to hearing about them and welcome your suggestions E Reuven M Lerner is a Web developer consultant and trainer He recently completed his PhD in Learning Sciences from Northwestern University You can read his blog Twitter feed and newsletter at http lerner co il Reuven lives with his wife and three children in Modi in Israel LEELECEOIECETTECCTEEETCEEETEEET T Send comments or feedback via http www linuxjournal com contact or to ljeditor linuxjournal com WWW LINUXJOURNAL COM OCTOBER 2014 37 COLUMNS WORK THE SHELL Picking Out the Nouns DAVE TAYLOR Dreamer
18. located at the ground station In the Amateur module you get one ground station called sample You can add more ground stations by 24 OCTOBER 2014 WWW LINUXJOURNAL COM clicking the down arrow and selecting contiguration Figure 3 You can add another ground Station by clicking the plus sign This will pop up a details window where you can enter a name and the location data for your ground station Figure 4 For the location you can enter the latitude and longitude t UPFRONT Name Home sss Description Ps Location Fredericton New Brunswick dhySelect Latitude 45 8667 North Longitude 66 5333 vie West 5 Locator FN6SRU Altitude 20 masl Weather St CYFC select Cear e OK Figure 4 You can add a ground station with details here manually or if you live in a major module It might make the display a tad city you can select it from a global crowded but it still should work list of locations should take a step back at this One other item you will notice when point and describe some other you have the configuration window contiguration options available open is that you can select which The first option to look at is the satellites are displayed This list is rather menu item Edit Update TLE This large but there is nothing stopping option lets you update the Keplerian you from adding all of them to your elements for the satellites
19. olen t Spy Eh li iit eee gt oo It ha tiiti ititi mp y PRETE as BPISee spisi Ris T ais Cc RIS z 4 microSD Cord Figure 1 The BeagleBone Black board isn t she beautiful E A light desktop system if you add a 5VDCC external power Supply an HDMI cable a screen keyboard and mouse This article focuses on working on a BBB from a Debian system with Python and some minimalism in mind But this is still a fully fledged Linux system not an Arduino or microcontroller In this article describe how to WWW LINUXJOURNAL COM OCTOBER 2014 83 FEATURE Accessing the I O Ports of the BeagleBone Black with Python There is no X session no fancy Web interface just the good old command line via SSH and the applications are launched automatically at boot via etc rc local access some of the I O ports E The serial ports to read and write on devices with an RS232 interface like a GPS for example m The GPIOs which allow you to trap or send TTL signals drive a relay read a button status and in particular let you add a PPS to Linux E The analog input voltage for reading voltages coming from a lot of sensors E Components on the i2c bus an RTC handled by the system and a DAC driven from your applications finish the article explaining how to use the BBB as a time server thanks to a GPS What Do We Use It For In our project the BBB boards are embedded in small compartments
20. tA E WWW LINUXJOURNAL COM OCTOBER 2014 59 FEATURE Raspi Sump The four pins on the sensor are wired to the Raspberry Pi as follows E Pin 1 VCC connects to the 5V pin 2 E Pin 2 Trig connects to GPIO17 pin 11 E Pin 3 Echo connects to GPIO27 pin 13 E Pin 4 Ground connects to pin 6 Ground chose GPIO17 and 27 but you can use any available GPIO pins on the PI as long as they are identified properly in the Python script Pin 1 provides 5V of power to the HC SRO4 sensor A command is Initiated on GPIO17 Trig that sets the value of the pin to True for 10 micro seconds This causes the sensor to initiate a series of sound pulses toward the water for that short amount of time The Echo pin connected to GPIO27 listens for a return pulse The difference between the send and the return of the pulse gives a time measurement The measurement is used to calculate the distance of the water This causes a small problem as Raspberry Pi GPIO pins are rated only for 3 3V The sensor sends a 5V current back toward GPIO27 60 OCTOBER 2014 WWW LINUXJOURNAL COM A way is needed to throttle the current to 3 3V which won t damage the Pi To protect the Pi from damage simply insert a voltage divider on the Echo line between the sensor and the Pi Voltage Divider The purpose of a voltage divider is to reduce the amount of current sent from one component to another As shown in Figure 1 soldered a 470R Ohm
21. the default environment you can use the env command env default f var The above command would forcibly Resources reset the specified variables to a value from the default environment To restore the complete environment from the default invoke the following command env default a The env command is very powerful you can use It import export environment data trom to RAM Final Comments The U Boot environment can act as a very useful runtime configuration tool When combined with scripting it can make the arduous task of development and testing boot scenarios much simpler and more fun to do sachin Verma is a Linux kernel Engineer with STMicroelectronics Pvt Limited His interest areas include the Linux kernel virtualization and multicore computing He can be reached at simplysachin gmail com POUT UP EAPO ROO RORCORODUORUODORTODUUTORRORODTOROUTORUORERUOROET Send comments or feedback via http www linuxjournal com contact or to Ijeditor linuxjournal com U Boot Source Code http git denx de u boot git Das U Boot Development Wiki http www denx de wiki U Boot WWW LINUXJOURNAL COM OCTOBER 2014 81 FEATURE Accessing the I O Ports of the BeagleBone Black with Python Accessing the I O Ports of the BeagleBone Black with Python The BeagleBone Black is a wonderful little piece of hardware You could use it to send your next rocket to Mars with just a few lines of Python
22. ve ever owned And it was less than 100 The EdgeRouter Lite is a business class router based on the open source Vyatta system It has been forked and as it matures it will become less and less like the original Vyatta code but for the present it works much the same purchased the EdgeRouter because my old ATOM based ClearOS router Tirewall couldn t keep up with the traffic from my home network My favorite features include E Three GigE ports each routable separately E A claimed one million packets per second throughput E Wire speed routing m Advanced configuration possible E Price l Il admit setting up the EdgeRouter Lite was a pain in the rear end The basics can be done via the Web interface but if you want any QOS for your connection it will be a learning experience trying to figure out the Vyatta command and code and concepts for doing so It took me three or four hours to get the setup that I m happy with and since then haven t touched it at all It works so fast never notice it and it s been rock solid since day one If you re looking for an advanced router but don t want to break the bank the EdgeRouter Lite might be exactly what you re need Be warned however its setup is not for the faint of heart SHAWN POWERS WWW LINUXJOURNAL COM OCTOBER 2014 19 UPFRONT The Cow Says Have Fun spowers server cowsay Shawn needs to spend 1 ess time on the command Line
23. Cat5 wire is securely taped to the sump pump s ABS pipe and an open wall stud to prevent tangling and WWW LINUXJOURNAL COM OCTOBER 2014 61 Figure 3 Open Sump Pit View ez Figure 4 Finished Pit View 62 OCTOBER 2014 WWW LINUXJOURNAL COM disconnection of the wire when removing the sump pit lid Finally the Raspberry Pi is mounted on a wall stud and plugged in to a UPS unit Figure 4 shows the finished view The Raspi Sump program currently consists of three Python scripts The main script is rasopisump py The script is very simple and is only about 100 lines of code The first thing it does is set the variables of the sump pit like depth 72cm critical water level 35cm and GPIO pin assignments as mentioned earlier The script then takes a sample of 11 water level readings every minute and uses the median sample as the best reading more on this later Once the reading is established the script determines if the water is ata sate or critical level Sate levels are logged to a CSV Tile and the script waits for another minute to take the next reading Critical levels are passed to a function that logs the level to the same CSV file and initiates an SMS e mail to my cell phone Figure 5 use the Python smtplib module to handle e mail alerts You can configure any e mail server to handle the alerts including a localhost mail server on the Pi if your ISP allows port 25 traffic
24. The reasons VLANs and NAC network access control systems exist is to prevent undesired access to various systems When you re designing or redesigning your network don t assume an external firewall will protect you from computers outside your network Disgruntled employees malware victims or nerdy employees like me will find a way to access systems from the outside Make sure their point of entry doesn t give them access to systems they shouldn t have access to in the first place THE OPEN SOURCE CLASSROOM Today s little tutorial isn t really hacking We re not doing anything the protocols aren t designed to do Heck all the tools are available pre packaged in your distribution don t want anyone to spend too much effort trying to block my attack because it s not an attack at all It s just using the tools available in exactly the way they re supposed to be used SSH is my favorite command line utility It can do so many things from transferring files to tunneling X11 traffic As described here you also can reroute traffic over tunnels giving you access to systems that shouldn t easily be accessible Ultimately hope learning about SSH will get you interested in network security because until you understand the danger there s not much motivation to learning and implementing such systems Until next time happy tunneling m Shawn Powers is the Associate Editor for Linux Journal He s also th
25. by two with two resistors as it must not be greater than 1 8V And we wire the output of the resistors to P9_ 39 AINO The vRef for the MCP4725 is VMAX 3 38V so the voltage we send is V maz x05 outV alue w 1 69 x V out outV alue 1006 1006 The vRef for the AIN is always 1 8V so in order to convert our 12 bit numerical value into a voltage reading we have ee es 18 V in nValue x I For a numerical raw value out we must read a numerical raw value in such as 7 l 1 69 inV alue int outV alue x aa Read AINO from sysfs If the BBB ADC kernel driver is not loaded load it now with echo BB ADC sys devices bone capemgr 8 slots If you need it loaded automatically at boot do like we did for the BB UARTs see the Passing Arguments at Boot Time sidebar To read a raw numerical value on AINO cat sys bus iio devices iio deviced in_voltage0 raw 3855 Is the Input Consistent with the Output We can see that the value WWW LINUXJOURNAL COM OCTOBER 2014 101 FEATURE Accessing the I O Ports of the BeagleBone Black with Python Table 3 Discrepancies between DAC Output and ADC Input OUT raw value IN theoretical raw value IN read raw value C A e C E w o e sent to the MCP4725 is correctly configuration Our control loop driving reread on AINO Table 3 our propeller s soeed can better handle The values match but there still the re injection of the output voltage
26. changes and then test the macro by typing t For macro s type qs to enter macro mode and assign the macro to the s key Then type gg again to anchor to the top of the Tile Next type SOA lt Enter gt to move to the SOA line Then type root lt Enter gt to move to the beginning of root example com and then type cwdnsadmin lt Esc gt to change that word to dnsadmin and exit insert mode Next type j to move the cursor to the beginning of the following line Finally type w lt Ctrl a gt to move forward to the serial number and increment It and then q to exit macro mode The complete set of macro keystrokes becomes qsgg S0OA lt Enter gt root lt Enter gt cwdnsadmin lt Esc gt jw lt Ctrl a gt q And again save the macro and use u to undo the change and replay it with s to make sure It does what expect For macro n type qn to enter macro mode and assign the macro to the n key Then type gg to anchor 44 OCTOBER 2014 WWW LINUXJOURNAL COM to the top of the Tile Next type ns1 lt Enter gt to move to the line that configures the name servers At this point there are a few ways could edit these lines My preference is to type IN A lt Enter gt 2w which will move my cursor to the beginning of the IP Then type c 10 1 0 250 lt Esc gt to edit to the end of the line and exit insert mode Since ns2 is so similar to ns1 can just type yyp lt Ctrl a gt lt Ctrl a gt to copy and
27. different social networks I ve played with such APIs in the past so wasn t new to their use in my applications but this book described a number of uses didn t think of with lots of clear example code that illuminated the points For those who want to analyze large data sets more directly Doing Data Science by Cathy O Neil and Rachel Schutt and published by O Reilly ISBN 9781449358655 is a dense but interesting introduction to the techniques that are collectively known as Data Science The authors give a whirlwind tour of the math and algorithms used in such analysis and also the types of conclusions you WWW LINUXJOURNAL COM OCTOBER 2014 35 COLUMNS C AT THE FORGE can draw from its use Some of this book was a bit heavy for my needs and interests but it gave me a much better sense of what the Data Science people are doing and how it Is already becoming useful should note that Cathy O Neil one of the co authors of this book is a participant in the new Slate Money podcast If you want to hear financial analysis driven by big data you might want to tune in to that weekly recording Freelancing and Business I ve been a freelance consultant since 1995 working with clients around the world and really enjoy my work even participate in a weekly podcast The Freelancers Show in which panelists discuss different aspects of what It s like to be self employed Two of my co
28. his wife Lucie and five year old son Nicholas He works as a Team Leader and Technical Advisor in Platform Virtualization Services for Shared services Canada and has been a Linux enthusiast and advocate since 1997 He loves all technology whose purpose is to increase quality of life He is user AL_Audet on Twitter PTET RR PURO ORCORORORUORORURRORORORUOUORORUOUORORUDRORORODUER Send comments or feedback via http www linuxjournal com contact or to ljeditor linuxjournal com Raspi Sump Web Site http www linuxnorth org raspi sump Source Code https github com alaudet raspi sump Quick Start Guide https github com alaudet raspi sump tree master docs MIT License https github com alaudet raspi sump blob master License HC SRO04 User Manual http www linuxnorth org raspi sump HC SRO4Users_Manual pdf Adam Lappin s Byte Creation Blog http www bytecreation com blog 2013 10 13 raspberry pi ultrasonic sensor hc sr04 WWW LINUXJOURNAL COM OCTOBER 2014 67 U Boot Environment Variables A close look at the anatomy of the U Boot environment SACHIN VERMA as U Boot is a popular D bootloader for embedded systems This wide adoption of U Boot is hardly surprising given the number of architectures and platforms it supports Additionally U Boot has a flexible compile time configuration setup You can select different features and drivers via config options and build a custom bootloader image for
29. in fact Here it is https www flickr com photos docsearls 14861798514 in set 72157646284287131 So why Linux We love Linux here but not all computer science education starts with Linux especially for kids But you started there which is very cool WWW LINUXJOURNAL COM OCTOBER 2014 111 EOF Between the two poles of servers and smartphones and the ubiquity of computers we think the majority of users will eventually run a Linux distribution JN Linux is the future So we hope Between the two poles of servers and smartphones and the ubiquity of computers we think the majority of users will eventually run a Linux distribution One of our goals is to remove the economic barrier associated with learning computer science Not only are the majority of Linux distros Tree they are amazingly powerful and customizable and can breathe new lite into old hardware Linux is also very hands on and learning it is also learning how a computer works Other popular operating systems obscure the inner workings of the computer from the user With Linux students can choose how deep they want to dive into their machines DS And you do all your production on Linux JN Yes We have such an appreciation for this operating system that we challenged ourselves to produce all 112 OCTOBER 2014 WWW LINUXJOURNAL COM of our media using Linux machines We edit our videos with Lightworks http www lwks com Ou
30. know where they work on ask the developers and make up patches He added Perhaps a few developers could be auditing the new Kconfig items of every kernel around rc3 time frame to ensure that they don t do stuff like this Jean said that rc3 would be too late because all kernel developers and distributions have already moved to the new kernel so they have already answered the n m y question for all new entries He added It s the reviewer s job to refuse new drivers with bad Kcontig descriptions in the first place This must happen as early as possible in the chain No clear decision came out of t UPFRONT the discussion but it does seem as though there s a vast mountain of configuration options that are becoming more and more difficult to deal with Eventually think some form of clean hardware dependencies will end up being implemented along the lines of Jean s suggestion With all the new devices coming out on the market there s a big desire to get Linux running properly on all of them Things like Intel s Quark system use only a few MB of RAM and have other tight hardware requirements Shrinking Linux down to the right size poses a challenge Andi Kleen recently pointed out One problem on these small systems Is the size of the network stack Currently enabling IPv4 costs about 400k He wanted to give users the option to prune down the Linux networking Stack to only the bare esse
31. minutes Danger you need to power the board with an external 5VDC power supply when flashing In order to use the armhf version Booting the BBB from an SD Card Power off the board then with the SD card inserted hold down the S2 button near the SD slot apply power and continue to hold down the button until the first LED comes on 86 OCTOBER 2014 WWW LINUXJOURNAL COM lf an NTP server is available to your BBB good for you but as the BBB lacks a backed battery RTC it doesn t retain date and time after reboot so you will have to take a few measures partition and format your SD card following the armhf site instructions at http www armhf com boards beaglebone black bbb sd install You then can download a recent armht rootfs archive http s3 armhf com dist bone debian wheezy 7 5 rootfs 3 14 4 1 bone armhf com tar xz and copy it to your SD Then when booting from the SD you likewise can copy your SD installation to your eMMC As the time of this writing July 2014 these Debian images come with Linux kernel 3 8 13 This version brought many improvements to accessing the BBB hardware by the kernel via sysfs Here is a list of packages recommend tor working with the board trom the shell and from Python apt get install kbd locales htop vim screen rsync build essential git python setuptools cython python pip python virtualenv python dev manpages dev posix dev glibc doc reference
32. mix Thanks for pointing that out Good stuff Norbert responds Thanks for responding to my earlier e mail Those constants are determined to make it work accounting for the fact that different months have a different num ber of days even going over centuries and so on It is hard to understand the algorithm however the result is a fast accurate algorithm Testing was done on sample data and after verification no further tests are needed as part of the algorithm Of course one needs to be very careful when cutting pasting lines In order not to screw it up PS We still code in FORTRAN partly because we inherited a large body of code in our area of research and partly because the code is really easy to write and etticient it pays off when dealing with billions of star positions It even still can be done on a modern laptop Suggestion am working for a telecom vendor on OSS products Lately I ve been working on NFV related meetings and workgroups There is a lot going with NFV all around telco operators and almost all will run LETTERS PHOTO OF THE MONTH I m writing to share this magnificent Linux laptop which believe is one of the smallest around It s a Zipit Z2 and l m a big fan of It Thanks to Johannes trom Wejp k vu I m able to host my Web site on this beauty Miatias Pen amp t Oa HE TOP Lists WWW LINUXJOURNAL COM OCTOBER 2014 13 LETTERS on Linux KVM OpenStac
33. options passed to the kernel just See the Passing Arguments at add them separated by a space like this Boot Time sidebar Okay but Does It Work To test the serial lines we just have to connect two of them together Figure 5 Now launch a screen session Figure 5 Direct Connection between UART1 and UART4 92 OCTOBER 2014 WWW LINUXJOURNAL COM Table 1 Direct Connection of UART1 with UART4G UART4_Tx PIN __13__ of P9 PIN 26 _ of P9 UART1_Rx IN 11 IN 24 UART4_Rx P of P9 P of P9 UART1_Tx on UART1 with screen dev tty01 check that what you type in one 115200 split your window with a window appears in the other Ctrl A S move to the next window Figure 6 with Ctrl Tab open a screen on From now on you can use UART4 with Ctrl A then type the python serial module to screen dev tty04 115200 and read and write on your serial ports A B if iy i l B i ea T pla i 7 T is F a prs mr m P 5 IE J ht z i i a tg aaa kai Ne aa z as a E a ire PET a _ e s 2 z j al y Eas iii p ay 5 p i i all H rt e 2 a oa Figure 6 ttyO1 and ttyO4 Screen Session WWW LINUXJOURNAL COM OCTOBER 2014 93 FEATURE Accessing the I O Ports of the BeagleBone Black with Python like this import time from serial import Serial ctrl_panel Serial port comport baudrate 9600 bytesize 8 parity N stopbits 1 timeout 0 25 send a commande ctrl_panel
34. panelists from the show have come out with eBooks during the past year Curtis McHale wrote Don t Be an Idiot Learn to Run a Viable Freelance Business http curtismchale ca products run viable freelance business which gives practical advice for starting and running a successful freelance business Along the same lines Eric Davis has a practical day by day plan for you to start on the freelancing track In his 30 Days to Become a Freelancer http theadmin org 30 days become freelancer 36 OCTOBER 2014 WWW LINUXJOURNAL COM Other Books Of course don t read only technical books although my friends and family might not quite believe that claim have read a number of excellent books in the past year that think you all might enjoy Tim Harford is a well known economics writer and has published numerous books on the subject His most recent The Undercover Economist Strikes Back describes how macroeconomics and government policies work and the various theories that economists have used to try to understand these policies and their effects have long had an interest In economics but still very much enjoyed reading this book which shed new light on the differences between various schools of economics Another favorite writer of mine Tom Standage came out with a new book this year Writing on the Wall Social Media The First 2 000 Years Standage s argument is that just about every type of social med
35. paste ns1 increment ns1 to be ns2 then move to the end of the line and increment the IP Next need to find the existing ns2 line and delete it with 4ns2 lt Enter gt dd Finally can type q to save the macro The complete macro is qngg ns1 lt Enter gt IN A lt Enter gt 2wc 10 1 0 250 lt Esc gt yyp lt Ctrl a gt lt Ctrl a gt ns2 lt Enter gt ddq Although this seems like a lot of text it will save a ton of work when you have to repeat the steps on multiple files For the final macro w type qw to enter macro mode assigned to the w key and then type G to move to the bottom of the file this time COLUMNS Then type 4worker lt Enter gt N to search for the next worker which will wrap around to the top then N will move back to the last worker in the file Finally type yyp to copy and paste the line then lt Ctrl a gt lt Ctrl a gt to increment both the worker hostname and the IP Finally type q to exit macro mode The complete macro is then qwG worker lt Enter gt Nyyp lt Ctrl a gt lt Ctrl a gt q Like the others test it out with w a couple times and use u to undo all the changes in between until am satisfied that it works Now that have all of these macros recorded could just open each Tile and type t to update the TTL s to edit the contact information and serial n to update the name servers and type 50 w to add 50 more workers Because I m going to p
36. python serial python smbus python Lxml python psutil i2c tools For interfacing with a GPS with a PPS apt get install gpsd python gps pps tools bison flex git core If you want to play with NTPd apt get install ntp Configure the System What Time Is It If an NTP server is available to your BBB good for you but as the BBB lacks a backed battery RTC it doesn t retain date and time after reboot so you will have to take a few measures First enter the date in UTC manually before anything else date u 0 2314512014 30 Wed Jul 23 14 51 30 UTC 2014 If your BBB must be isolated from an NTP server one solution is to add an RTC to the board like a ds1307 I will show how to add one on the i2c bus WWW LINUXJOURNAL COM OCTOBER 2014 87 Finally if you are isolated and without an RTC module try the fake hwclock package from the Debian repositories It will allow your clock to restart with the last Configuring the Network Card Static Edit the etc network interfaces file and change the line reading iface ethO inet dhcp to Q c 1 iface ethO inet address 192 1 netmask 255 2 roadcast 192 st 16 A U1 CO v VI N L s m O e oe _ LO DO S ep oe H Then restart networking with etc init d networking sto etc init d networking Note if you are editing the file via SSH you will lose your connection right now You shou
37. science definitions and more The app version contains a variety of features that aid learning such as a Flash Card Quiz search and navigation such as full text search and convenience no Internet connection required http Awww cambridge org and http www slovoed com Imagineer Systems Ltd s mocha Pro Visual effects solutions developer Imagineer Systems Ltd says that it has made its mark on such films as The Hobbit Black Swan Transformers and the Harry Potter series The latest release in Imagineer s creativity toolkit is mocha Pro 4 the company s updated standalone software utility optimized for visual effects and post production challenges Key existing mocha Pro features include a rock solid planar motion tracking engine advanced roto tools 3 D camera solver stereoscopic 3 D support calibration of lens distortion stabilization module and insert module New features found in version 4 include new advanced tools for stereoscopic 3 D customizable keyboard shortcuts Adobe Premiere support Python scripting improved format support and more http www imagineersystems com 52 OCTOBER 2014 WWW LINUXJOURNAL COM NEW PRODUCTS Checkmarx Game of Hacks What vulnerability exist in this code 5 E pmoninerorparoin In its new on line game Game of Hacks Checkmarx Me allows developers to have fun while honing their security skills and understanding of the hacker s perspective In the game developers and se
38. to encounter a company that is using Python 3 all of my consulting and training clients still use Python 2 7 However there s no doubt that Python 3 x is the future COLUMNS and Lutz has done us all a good service by providing such intormation This is not a book about learning Python but rather it s meant to be a reference and in depth description of how the language works And at that it succeeds At the same time Teel like the book is far too large at more than 1 600 pages 400 pages of which are spent describing Tkinter a GUI toolkit that is included with Python is easy to use and is cross platform But it s also extremely ugly and not particularly popular in my experience If you re a Python programmer though you ll likely want to have this book on your shelf When I m teaching Python programming classes my students often ask me how they can boost the performance of their code True think that Python like many other high level languages stresses programmer efficiency over language efficiency And of course we know that worrying about performance too early in a project is asking for trouble At the same time once our program is working we definitely want to increase its soeed Python High Performance Programming written by Gabriele Lanaro and published by Packt Press ISBN 978 1 78328 845 8 aims to solve some of these issues The book concentrates on a small number of areas that can be us
39. to monitor the water level in a sump pit log the readings and send SMS e mail alerts if the water rises above a predefined level In this article show the methodology used to create Raspi Sump also describe the physical setup of the monitor and the scripts that make It work If you choose to do something similar the source code and install instructions are available on GitHub WWW LINUXJOURNAL COM OCTOBER 2014 57 FEATURE Raspi Sump With the help of a Python script the sensor which is mounted inside the sump pit facing the water sends a sound pulse that reflects off the water and back to the sensor It is Tree to use and modify as you wish see Resources determined that the features required in a monitor included the following E Regular one minute interval readings of the water depth in my sump pit E Logging of readings to a comma delimited file for processing graphs and historical pump activity m Automated SMS e mail alerts if the water exceeds a predetined level M Off site graphical reports of the current water level to a Web site E Web based historical information on sump pump activity m Automatic restart of the raspisump py process after an unexpected failure The Physical Setup The complete list of components for 58 OCTOBER 2014 WWW LINUXJOURNAL COM Raspi Sump includes Raspberry Pi Model B and case Raspbian Linux HC SRO4 ultrasonic sensor Five feet of C
40. write pupitre_ commande read an answer buff ctrl_panel read answer_ size as the serial port is configured non blocking with timeout 0 25 we make sure all the bytes asked for are received while Len buff lt answer size n len buff b ctrl_panel read answer_size n buff b time sleep 0 02 print Serial IN print join 02X ord c for c in buff The python serial module is quite efficient We managed to read two serial ports refreshed at 50Hz plus a third at 5Hz on the same board and simultaneously with a few glitches between the timestamps and the CPU load stayed below 50 The GPIO The General Purpose Input or Output pins allow the 94 OCTOBER 2014 WWW LINUXJOURNAL COM board to receive a signal read a frequency on input or drive a relay on output First we had to understand the mapping between the pin on the P8 and P9 connectors and the GPIO numbers as seen by the kernel The BBB System Reference Manual gives the Expansion Header P9 pinout http elinux org Beagleboard BeagleBoneBlack Hardware_Files For each GPIO the name is made up of the GPIO controller number between 0 and 3 and the pin number on the Sitara AM3359AZ The kernel numbers the GPIO pin with PIN GPIO controller number 32 If we pick the GPIO1_16 on the pin 15 of the P9 connector the kernel will see it as GPIO_48 164 1 32 See Figure 7 to read the direct mapping for all the GPIOs And
41. years The name DevOps is a portmanteau of Development and Operations and is meant to denote a fusion of these two functions in a company Whether or not your business actually does combine the two functions the lessons and tools learned from the DevOps movement and attitude can be applied throughout the entire Information Technology space This eBook focuses on one of the key attributes of the DevOps movement Quality Assurance At any point you should be able to release your product code or configuration so long as you continue keeping your deliverables in a deployable state This is done by slowing down to include a Quality Assurance step at each point in your workflow The sooner you catch an error or trouble condition and fix it the faster you can get back on track This will lower the amount of rework required and keep your team s momentum going in a forward direction enabling your group to move on to new projects and challenges C GEEK GUIDE Build a Private Cloud for Less Than 10 000 This eBook presents a compelling argument as to why you should consider re architecting your enterprise toward a private cloud It outlines some of the design considerations that you need to be aware of before implementing your own private cloud and it describes using the DevCloud installer in order to install OpenStack on an Ubuntu 14 server Finally this eBook will familiarize you with the features and day to day ope
42. your platform U Boot s flexibility is extended at runtime as well Using U Boot environment variables you can influence the program execution flow U Boot comes with a CLI command line interpreter which has basic scripting capabilities This scripting ability combined with the U Boot environment variables can be used to create some powerful booting scenarios The ability to manipulate program behavior using environment variables is beneficial for both development and production setups alike During development people strive to test all possible paths for loading and booting images for their platforms So you may try to load a Linux kernel image from a local storage Flash SDcard USB eMMC and so on or access it over the network NFS TFTP and so on U Boot simply makes your life easier as a developer You just need to tweak the scripts combining environment variables in a fruitful way Production images also need some versatility When a product s OS images need an upgrade the bootloader must be configurable to fetch the images trom different sources U Boot has a number of system variables that you can modify to achieve your desired results For example on certain systems initrd images loaded on top of DDR may not be accessible to the Linux kernel To counter this you can instruct U Boot to load initrd at a lower DDR address You can do this by setting the initrd high environment variable Another common sit
43. 2014 WWW LINUXJOURNAL COM version and it looks best I think on a large format color tablet If you look back the older PDF versions were even more difficult to read on a computer screen as the layout mirrored the paper version exactly know you said you don t like the EPUB version but I m not sure whether you ve tried reading the EPUB on a computer screen or only on eReaders Using something like Readium http www readium org you can change the font size and read the text in a single column Apart from that I m not sure what else to suggest l m not sure what you dislike about the EPUB version so I don t know how to help there if Readium doesn t work for you Shawn Powers Subscription Question carry two tablets one iOS and the other Android If subscribe on my iPad to Linux Journal can also read it on my Nexus 7 Greg If you subscribe directly through Linux Journal we will send you monthly notices with download links for epub pdf mobi and browser versions of the magazine You also will get access through our Android or iOS apps We want our subscribers to be able to access the issues in any format that is available If you order through Google Play or iTunes you will receive only those versions Both have subscription options but they are pretty much a closed environment We want you to be able to access the magazine any way you choose If you subscribed through Google
44. Debian Stable to Debian Testing First update your system with apt get update amp amp apt get upgrade Next modify your etc apt sources list d debian list file Copy the lines with wheezy or stable and replace all occurrences of wheezy with jessie on the copied lines You can choose testing instead of jessie if you want to keep on with the testing release after jessie was made stable Then launch apt get update amp amp apt get upgrade again and if all is well it might take a long time depending on your connection quality and the packages already installed run apt get dist upgrade The BBB accepts booting from the internal memory the eMMC or from an external SD See the Booting the BBB from an SD Card sidebar To test another version of the system simply download and write it on your SD If you are satisfied with it you have the option to put it on the eMMC As the environment hosting our BBBs is subject to strong vibrations chose to put my system in the eMMC rather than on an SD Flash the eMMC In order to flash your new system to your eMMC download the flasher version from eLinux or the official one Write it to your SD and boot your BBB from the SD The flashing process happens automagically You will have to wait less than ten minutes before the four blue LEDs become steady indicating that the flashing is over As the official firmware is much larger the flashing will take a lot longer 45
45. Hacks and Ubuntu Hacks He is currently the president of the North Bay Linux Users Group PEE Send comments or feedback via http www linuxjournal com contact or to ljeditor linuxjournal com WWW LINUXJOURNAL COM OCTOBER 2014 45 COLUMNS THE OPEN SOURCE CLASSROOM This Is Why SHAWN POWERS We Can t Have Nice Things SSH Firewalls are great but don t rely on them as your only network security I ve written about SSH before often even But for the Linux user SSH Is one of those tools that Is so incredibly flexible everyone should know and understand It inside and out For this article decided to put on my black hat and demonstrate how convenient and territying SSH can be Phone Home Most articles on SSH start with forwarding X11 traffic or demonstrating the SOCKS proxy feature want to start with something a little more creepy and a whole lot more awesome The premise is this you have a computer inside a firewalled NAT d network and you want to access it remotely If you re the sysadmin you can just forward a port on the firewall 46 OCTOBER 2014 WWW LINUXJOURNAL COM into the computer If you re not however you can use SSH to open a tunnel for you automatically This does require a few things E You need a server running SSH with a public IP address use my co located Raspberry Pi in Austria but you can use your home connection as long as you set u
46. Linux as well U Boot provides a set of utilities called fw _printenv and fw setenv to do the job First you need to compile these utilities for Linux Figure 9 shows the compilation steps for the utility Here am cross compiling it for the ARM plattorm It is a multi call binary So you need to make a symlink named fw setenv to the binary fw_printenvy To modify the environment you first need to boot in to Linux on the target board Next you need to create a Tile called etc TWw_env config This tile contains all the information needed to specify the location of WWW LINUXJOURNAL COM OCTOBER 2014 79 FEATURE U Boot Environment Variables make lt your board gt config make HOSTCC armv7 linux gcc HOSTSTRIP armv7 linux strip tools all Figure 9 Compiling fw_printenv fw_setenv for an armv7 Host root Deepthought cat etc fw_env config MTD device name Device offset Env size Flash sector size Number of sectors dev mtd0 0x80000 0x4000 0x10000 a Configure where your environment resides in flash root Deepthought fw_printenv baudrate 115200 bootdelay 10 load _addr 40000000 b print currently set environment variables of U boot root Deepthought fw_setenv fdt_high 0x80000000 root Deepthought cat list txt phrase The quick brown fox jumps over the lazy dog initrd_high 0x90000000 root Deepthought fw_setenv s list txt root Deepthought fw_printenv baudrate 115200 bootdelay 10 i
47. Logic wikl See also the work of Fabien Le Mentec Using the BeagleBone PRU to achieve real time at low cost http www embeddedrelated com showarticle 586 php Conclusion The BeagleBone Black is a very fun platform to play with As a Linux sysadmin for nearly 20 years I m very comfortable using it to access electronic hardware l m not so well Resources acquainted with usually want to thank my co worker Rodolphe Pella whose skills in electronics were essential in connecting all the components to the board He did our four homemade Capes in no time and did them well The community orbiting the BBB is large with a lot of good on line resources We managed to learn some complex stuff in very little time and with almost no confusion because we can profit from the work of those people and from the Linux and Python ecosystems E Samuel Bucquet is a system developer and a sysadmin on robotic platforms in the French DOD He is married with four kids and lives in Brest France and he is a longtime Linux aficionado TOUTE PERU OR ODER UOROD TORU ORORTOROOUORUORODTORUUUORUOREDUOROET Send comments or feedback via http www linuxjournal com contact or to ljeditor linuxjournal com You will find the source of the Python code used in this article on my GitHub account https github com samgratte BeagleboneBlack PyBBIO is a Python Library for the BBB mimicking the Arduino IO access by Alexander Hiam https gith
48. NETWORK SECURITY y and SSH What You J R N _ Since 1994 The Original Magazine of the Linux Community OCTOBER 2014 ISSUE 246 www linuxjournal com Sump Pump Monitor with interview Raspberry PIi with the nd Pvthon Creators and yt j of the Hello World Program Advanced at the U Boot Vim Macro Environment Techniques Anatomy L THINGS OPEN ICT 22 23 2014 RALEIGH CONVENTION CENTER In Raleigh and the Research Triangle A Global Epicenter of Technology and Open Source Innovation A CONFERENCE EXPLORING OPEN SOURCE OPEN TECH AND THE OPEN WEB IN THE ENTERPRISE LEADING TECHNOLOGY AND BUSINESS LEADERS WILL PARTICIPATE 3 i Lp MARTE WW CeyAVI Es JAMES TURN 12a s gt N Software Freedom Conservancy YEHUDA KATZ Tilde JOSEPH Two days of keynotes talks tutorials workshops and networking opportunities in Raleigh and the Research Triangle area REGISTER NOW ALL THINGSOPEN ORG SERVERS STORAGE o HPC Are you tired of dealing with proprietary storage GF a ZFS Unified Storage zStax StorCore ZFS Unified Storage from Silicon Mechanics is truly software defined storage From modest data storage needs to a multi tiered production storage environment the zStax StorCore ZFS unified storage appliances have the right mix of performance capacity and reliability to fit your needs O cto b er zSt
49. OURNAL COM some side effects to the changes done to some environment variable For such use cases U Boot provides a mechanism of deploying callback handlers You can associate a callback function with an environment variable As a first step you have to register a callback handler with U Boot This function would be called whenever you do any modifications to the environment variable Figure 6 shows Sample code to register a callback with U Boot You can place such handler code in your board specitic Tile The macro U_BOOT_ENV_CALLBACK registers the callback function on _change_ foo with the handler named foo_h Your handler is now registered with U Boot with the name foo include lt env_flags h gt include lt environment h gt Now you need to establish a link to this registered handler with an environment variable Take a look at the struct entry in Figure 6 You can see that there is a member named callback a function pointer for each environment variable U Boot would invoke this handler before committing the modified environment variable to the hashtable You can make this as sociation of callback handler with the environment variable either at compile time or at runtime For compile time association you need to define the contig option define CONFIG ENV CALLBACK LIST DEFAULT foo foo_h in your board s contig Tile You also can do runtime association as depicted in Figure 7 Here have static i
50. R 2014 97 The i2C Bus Two i2c buses on the BBB are available The kernel sees them as i2c 0 for I2C1 on P9_17 SCL and P9_18 SDA and i2c 1 for 2C2 on P9_19 SCL and P9_20 SDA Add an RTC to the BBB The DS1307 or the DS3231 are RTC modules with a battery keeping the clock running when there is no power The ChronoDot RTC with a ds3231 Is much more accurate and the ds130 7 is much less expensive Wire the RTC on i2c You can feed the 5VDCC of the board to the RTC module as long as you clip out TINY ACON le GASO O000AE orn LO ooa Sa fe 0000000r a 6 0000 5 e 2 9 o 10000 0000 100000000 00 Table 2 ds1307 Wiring on the BBB i2c_2 Bus the two 2 2k resistors Figure 8 The internal resistors of the BBB i2c bus will then be used Danger if you power the BBB over USB use P9_7 SYS 5V instead Enable the New RTC Declare the Figure 8 The Adafruit RTC ds1307 Module Wired on the BBB 98 OCTOBER 2014 WWW LINUXJOURNAL COM new RTC to the kernel echo ds1307 0x68 gt sys class i2c adapter i2c 1 new_ device 73 993241 rtc ds1307 1 0068 rtc core registered ds1307 as rtc1 74 007187 rtc ds1307 1 0068 56 bytes nvram 74 018913 i2c i2c 1 new device Instantiated device ds1307 at 0x68 Push the current UTC date to the ds130 7 hwclock u w f dev rtcl Verify the clock hwclock debug r f dev rtc1 hwclock from util linux 2 20 1
51. SET button for the other UARTs available on UART5 can t be used altogether the board with the HDMI output The BBB comes with six UARTs but three of them can t be addressed by So UART1 UART2 and UART4 our applications are the ones available and they are addressed respectively as UARTO is the serial debug on J1 dev ttyO1 dev ttyO2 and dev ttyO4 Note that only UART1 and UART4 UART3 lacks an RX line have CTS and RTS pins 90 OCTOBER 2014 WWW LINUXJOURNAL COM Figure 4 Our CAPE with Two MAX3232s Load the CAPE files for each UART for i in 1 2 4 do echo BB UART i gt sys devices bone capemgr slots done The output of dmesg should show a correct initialization dmesg grep tty 1 541819 console tty00 enabled 286 489374 48022000 serial ttyO1 at MMIO 0x48022000 irq 89 is a OMAP UART1 286 627996 48024000 serial tty02 at MMIO 0x48024000 irq 90 is a OMAP UART2 286 768652 481a8000 serial tty04 at MMIO 0x481a8000 irq 61 is a OMAP UART4 WWW LINUXJOURNAL COM OCTOBER 2014 91 Now you can ask the kernel to Passing Arguments load them at boot time Edit at Boot Time boot uboot uEnv txt and modify the line with optargs like this To give command line options to the kernel modify the optargs variable in optargs capemgr enable partno BB UART1 the boot uboot uEnv txt file Only one BB UART2 BB UART4 optargs line is allowed so if you need several
52. UXJOURNAL COM OCTOBER 2014 75 FEATURE U Boot Environment Variables typedef struct entry const char key char data int callback const char name const char value enum env_op op int flags int ENTRY Member flags is used to store bitmap containing type of variable and associated permissions Available variable type flags Available variable access flags Variable Type Name Flag Variable Access Name string a decimal read only hexadecimal write once boolean change default IP address MAC address Figure 5 Hashtable representation of an environment variable There is an associated callback function as well as a bitmap to store type and access control inside the hashtable is represented environment variable If defined this by a data structure called a struct callback handler would be invoked entry Figure 5 Apart trom the whenever any operation like add members key and data which delete or modity is performed on this correspond to name and value in environment variable the linearized representation of data you have members called callback How to Control React to and flags flags is of integer type Environment Variable Modification and is used to implement type check At times you may want to do your own and access control callbacks is the runtime configurations You may want callback function associated with this to react accept reject or produce 76 OCTOBER 2014 WWW LINUXJ
53. a sorted sample can remove those fringe readings at the high and low end if they occur The median reading is always accurate within one centimeter of the actual water level For a residential system am not concerned with millimeter accuracy A small variance in readings still provides safe reporting of the water level This also helps explain the jagged line in the graphs that are generated and sent to a Web server at regular intervals The second script use is todaychart py This script generates graphs as shown in Figure 7 of water level activity from my CSV log files It uses the Python matplotlib and NumPy modules to generate the graphs rsync over SSH copies the graphs and CSV log files hourly to my Web server via a cron script chose to generate graphs on the Pi instead of the Web server because different Linux distributions package different versions of matplotlib and NumPy prefer using the packaged versions for simplicity Always using the Raspberry WWW LINUXJOURNAL COM OCTOBER 2014 65 FEATURE Raspi Sump Pi renders more consistent graphs no matter which distro you use for your off site component The third and final script is checkpid py Its purpose is to monitor the health of the raspisump py process and restart it if it is stopped Cron runs the script at regular intervals and looks for one of three outcomes If the script returns O this indicates a failed process checkpid py then initiate
54. al marshmallows credit for slacking off at work er mean for discovering awesomeness m Star Wars open a terminal and type E mail shawn linuxjournal com telnet towel blinkenlights nl put something like FUN in the and grab some popcorn Or subject line so know what it s maybe roast some of those digital about SHAWN POWERS Powerful Rhino Tablet Raven Rhino M4800 M6800 e Dell Precision M6800 w Core i7 Quad 8 core e 15 6 17 3 QHD LED w X 3200x1800 e NVidia Quadro K5100M e 750 GB 1 TB hard drive e Up to 32 GB RAM 1866 MHz e DVD RW or Blu ray e 802 11a b g n e Starts at 1375 e E6230 E6330 E6440 E6540 also available aD Rugged Tarantula e High performance NVidia 3 D on an QHD RGB LED Tarantula CF 31 e High performance Core i7 Quad CPUs 32 GB RAM Panasonic Toughbook CF 31 e Ultimate configurability choose your laptop s features e FOUY Wseed eee tesla e One year Linux tech support phone and email drops dust moisture amp more e Three year manufacturer s on site warranty 131 XGA Touchocrecn e Choice of pre installed Linux distribution Gere ey I5 p to S j3 i 7 N E e 320 750 GB hard drive 512 GB SSD e CF 19 CF 52 CF H2 FZ G1 available Raven X240 e ThinkPad X240 by Lenovo e 12 5 FHD LED w X 1920x1080 e 2 6 2 9 GHz Core i7 e Up to 16 GB RAM e 180 256 GB SSD e Starts at 1910 e W540 T440 T540 also available Em pero E nux www EmperorLinu
55. alternatives For example he said users simply could compile everything as modules Then they d be loaded into the system only as needed But neither Jean nor Josh liked that suggestion Jean said that in the old days it was fine to build everything as a module but nowadays there were just too many modules and that Saying m to everything increases build times beyond reason You also hit build failures you shouldn t have to care about depmod takes forever updates are slow as hell This is the problem am trying to solve Greg didn t see how build times could be a problem Building the kernel on his laptop he said took about 20 minutes with all 3 000 modules compiled in If that wasn t good enough he suggested upgrading the hardware to get a faster build time But Jean said this wasn t a practical solution for some cases He said We have 34 kernel flavors for openSUSE 13 1 for example And every commit potentially triggers a rebuild of the whole set to catch regressions as fast as possible So every module we build for no good reason gets built a hundred times each day He added that it would cost a lot of money to upgrade the hardware underneath that build system Greg said he understood the Issue but that fixing the contig system was just a hard problem to solve It boiled down to enforcing better habits on everyone producing patches He said If you see new drivers show up that you don t
56. an t overwrite foo Error inserting foo variable errno 1 Deepthought gt Figure 8 Each environment variable can be associated with a type and access permission in the environment variable flags decimal hexadecimal boolean IP address and MAC address There are corresponding codes for these type modifiers s d x b i and m Again U Boot stores this type information of variables in flags as a bitmap Figure 5 You can associate type and access control to a variable either at compile time or at runtime For compile time association you need to define a contig define CONFIG ENV FLAGS LIST DEFAULT foo sr in your board Tile For runtime association you can define an environment variable flags Figure 8 Here am associating an environment variable foo with type s meaning the value is a string and access control r meaning it Is read only Once deployed if you try to modity the variable foo U Boot will reject your request Also if a value is not of specitied type your update to the environment variable will fail Environment variables like MAC address make use of type m This will make U Boot do a sanity check on the value entered by the user to confirm whether the value is indeed a valid MAC address Modifying the U Boot User Environment from Linux U Boot environment variables can be added modified or deleted from
57. ange the TTL HACK AND E Macro s will change the contact information and increment the serial E Macro n will update the name server records E Macro w will add one more worker Because I m going to chain these macros together it s even more important than in the past that make Sure my cursor is anchored in a known location first For the first macro this means starting with gg to move to the very top of the Tile while for the last macro will want to type G to move to the bottom of the Tile At each phase it s incredibly important that you test each macro then undo the changes and contirm that your macros work exactly how you expect Let s break down each macro For macro t first tyoe qt to enter macro mode and assign the macro to the t key Then type gg to make sure I m at the top of the file Next type TTL lt Enter gt to move the cursor to the TTL line Then type w to move forward a word to the actual TTL value want to change and then type cw10m to change the following word from 15m to 10m Finally press Esc to exit insert mode and q to exit the macro The complete set of macro keystrokes then WWW LINUXJOURNAL COM OCTOBER 2014 43 COLUMNS HACK AND Although this seems like a lot of text it will save a ton of work when you have to repeat the steps on multiple files would be qtgg TTL lt Enter gt wcw10m lt Esc gt q Once record the macro type u to undo my
58. app 108 OCTOBER 2014 WWW LINUXJOURNAL COM KNOWLEDGE HUB WHITE PAPERS E redhat Linux Management with Red Hat Satellite Measuring Business Impact and ROI Sponsor Red Hat Topic Linux Management Linux has become a key foundation for supporting today s rapidly growing IT environments Linux is being used to de ploy business applications and databases trading on its reputation as a low cost operating environment For many IT organizations Linux is a mainstay for deploying Web servers and has evolved from handling basic file print and utility workloads to running mission critical applications and databases physically virtually and in the cloud As Linux grows in importance in terms of value to the business managing Linux environments to high standards of service quality availability security and performance becomes an essential requirement for business success gt http Inxjr nI RHS ROI Standardized Operating Environments redhat for IT Efficiency Sponsor Red Hat The Red Hat Standard Operating Environment SOE helps you define deploy and maintain Red Hat Enterprise Linux and third party applications as an SOE The SOE is fully aligned with your requirements as an effective and managed process and fully integrated with your IT environment and processes Benefits of an SOE SOE Is a specification for a tested standard selection of computer hardware software and their configuration for
59. ar an understanding of what a commit is and how branches tags blobs and trees fit into this commit centric view of the world is the biggest obstacle to working with Git So was happy to see the Git Pocket Guide written by Richard E Silverman and published by O Reilly ISBN 9781449325862 Yes this book will helo you use Git better and it will remind you of many of the commands But more significant the Git Pocket Guide introduces you to the objects Git uses and describes how they work together to provide a robust and efficient version control system Databases and Analysis The growth of the Web has led not only to a growing need for people who can create Web applications but also for those who can store retrieve and analyze the data generated by those applications The term big AT THE FORGE data increasingly is applied to such programs and a number of books have been written in the past few years that attempt to help newcomers to the field In some cases you don t need to collect or analyze the data yourself Rather you can get by just using the APIs that various systems have provided This is particularly the case with social networks which collect enormous quantities of information about their members and the connections between them Mining the Social Web by Matthew A Russell was released in its second edition ISBN 9781449367619 and it describes many ways in which you can access and analyze
60. at5 wire four 24AWG Strands needed Two resistors one 470R Ohm and one 1K Ohm Heat shrink tubing to protect soldered connections Plastic bracket to hold the sensor One two Toot piece of wood strapping to mount the plastic bracket in the pit One floppy drive four pin power connector salvaged trom an old PC Two case fan power connectors also salvaged from the same PC Total cost tor materials including time it takes for the sound pulse a couple spare sensors was 80 to bounce back to the sensor It The ultrasonic sensor chose calculates the distance by measuring is the HC SRO4 which has four the time required for the pulse to connections that are wired to the return at the speed of sound This GPIO pins of the Raspberry Pi With gives you a reading of the distance the helo of a Python script the between the sensor and the water sensor which is mounted inside the The distance is used to calculate the sump pit facing the water sends water depth and log a time stamped a sound pulse that reflects off result to a CSV file the water and back to the sensor Figure 1 shows a closer look at The script monitors the amount of the connections Raspi Sump Wiring Diagram Raspberry Pi Model B HC SR04 Ultrasonic Sensor ti JMO g iq AagdsSEy IHIH g UNU wuauwd ISJ j sni Ohm Resistor ETHERNET 1K Ohm Resistor Ground USB Cx VW Figure 1 Wiring Diagram
61. ax StorCore 64 Featured Download 7 R a oS es Ga ek ees I J J i i a y i F Ieg A O00 Se 9 ae _ 220 a A ete at Negegest e i Q network Talk with an expert today 866 352 1173 www siliconmechanics com zstax CONTENT OCTOBER 2014 ISSUE 246 EMBEDDED FEATURES 56 Raspi Sump Put a Raspberry Pi with Raspbian Linux to work and protect your basement against flooding Al Audet 68 U Boot Environment Variables Everything you need to know about the U Boot environment Sachin Verma 82 Accessing the 10 Ports of the BeagleBone Black with Python With the BeagleBone Black you can command all your electronic gear with a few lines of Python Samuel Bucquet Cover Image Can Stock Photo Inc kgtoh 4 OCTOBER 2014 WWW LINUXJOURNAL COM x GPREDICT Amateur File Edit Help 2014 08 06 00 54 04 32 Reuven M Lerner s At the Forge 2014 Book Roundup 38 Dave Taylor s MENS Work the Shell WT e Picking Out the Nouns J S ar 42 Kyle Rankin s Hack and Raspi Sump Wiring Diagram Raspberry Pi Model B HC SR04 Ultrasonic Sensor Return of the Mac 46 Shawn Powers The Open Source Classroom This Is Why We Can t Have Nice Things SSH 110 Doc Searls EOF a on Learn GNU Linux the Fun Way a en roun IN EVERY ISSUE 8 Current Issue tar gz 10 Letters 16 UPFRONT 30 Editors Choice 52 New Products 113 Advertisers Index
62. aximizing the power of the standard library modules finding and utilizing third party libraries creating packaging and reusing libraries within and across projects building multilayered functionality including networks data and user interfaces and using development environments like virtualenv pip and more Publisher Wrox says that Python developers looking to apply their skills to real world challenges will find a goldmine of information and expert insight in Python Projects http Awww wrox com WWW LINUXJOURNAL COM OCTOBER 2014 53 NEW PRODUCTS AES CleverView for TCP IP on Linux 5 5 oo and CLEVER Mobile for Linux pape The CleverView for TCP IP on Linux solution from AES addresses the Server 137 72 43 136 Port 3306 UserID admin1 GAES q l l challenge in cloud based data centers that an ever greater amount of traffic is between servers preferably Linux based ones of course CleverView is a performance and availability monitoring solution for Linux UNIX and System z that has added new features in its latest v2 3 000 release Concurrently AES released an updated CLEVER Mobile for Linux so that enterprise knowledge workers can access server performance and availability details from their mobile devices The most noteworthy highlight of CleverView v2 3 is the SMF Host Utility that integrates Linux UNIX monitored metrics with z OS SMF records expanding enterprise insight into performance and avai
63. ber just how that worked This book introduces techniques that will helo you build asynchronous programs that are easier to understand and debug Functional programming Is a technique that was pushed aside for many years by object oriented programming but it s making a comeback Even if you re not using a purely functional programming language functional techniques are increasingly important and useful Functional JavaScript written by Michael Fogus and published by O Reilly ISBN 9781449360726 introduces a wide variety of functional ideas and techniques I d say that this book is good for two types of audiences those who already know functional programming and want to see how these ideas can be applied in JavaScript as well as the opposite people who know JavaScript and are interested in learning functional programming If you are new to JavaScript or if you have been using it only tor Web development and haven t yet learned how it works as a more general purpose programming language you may well want to read Eloquent JavaScript The book written by Marijn Haverbeke and available on line at http eloquentjavascript net and 34 OCTOBER 2014 WWW LINUXJOURNAL COM soon to be published in paper form by No Starch Press reviews the basics of JavaScript as a language ignoring the Web related aspects until halfway through the book So you learn about JavaScript objects higher order functions and even regular expre
64. choose the way it will operate If you want to process input signals echo in gt sys class gpio gpi048 direction Then choose if you want to detect a rising or falling edge or both echo both gt sys class gpio gpi048 edge If you want to output signals you can choose out or one of high or low telling when the Signal is active echo high gt sys class gpio gpi048 direction And to stop emitting the signal echo gt sys class gpio0 gp1048 value WWW LINUXJOURNAL COM OCTOBER 2014 95 FEATURE Accessing the I O Ports of the BeagleBone Black with Python At the end release the GPIO echo 48 gt sys class gpio unexport Wait for a Signal on a GPIO from Python We connected an optical water detector to one of our BBBs inside an enclosure on the GPIO_48 P9_15 Figure 3 The water detector sends a TTL signal if there is water passing through its lens Here is how we wait for an event describing water presence from Python using the BBB_GPIO class trom bbb_gpio py from bbb gpio import BBB GPIO water BBB GPIO 48 gpio_ edge both active_lLow True for value in water 1f value print Water detected else print No more water The BBB_GPIO class is a generator For each iteration we wait for a change on the GPIO and return in value the GPIO status When the GPIO is waiting for an event we don t want to be polling aggressively on the sy
65. connect to those Strange URLs with standard virtual hostnames SSH is such a powerful flexible tool that its uses are seemingly unlimited With that great power comes great responsibility though because SSH allows you to do some pretty creepy things Even Scarier You may have noticed that using an SSH tunnel provides you only with specific access to specific ports spelled out with the tunnel directives It is possible to pass multiple R flags but it s tough to do that on the fly because the command is performed on the computer inside the firewall If you need to access the entire network behind the firewall that s where sshuttle comes into play I ve mentioned sshuttle in past issues of Linux Journal but when used in conjunction with the tunnels just described how to create it WWW LINUXJOURNAL COM OCTOBER 2014 49 COLUMNS THE OPEN SOURCE CLASSROOM Home Computer runs sshuttle Firewall Figure 2 Using SSH tunnels and sshuttle together can provide an incredibly scary level of network access from outside the firewall turns into something that should be impossible but isn t Once you have the reverse tunnel established using the processes above the command to get you access to the entire Tirewalled network is another one liner sshuttle D r user remotehost 2222 192 168 1 0 24 As a reminder this runs on your home workstation not on the computer behind the corporate fire
66. curity protessionals test their application hacking skills improve their code security know how and facilitate better security practices in hope of reducing the amount of vulnerabilities in their applications Available for desktop tablet and mobile Game of Hacks presents developers with vulnerable pieces of code and challenges them to identity the application layer vulnerability as quickly as possible It even has a two player mode allowing head to head competition Players analyze vulnerabilities including SQL injection XSS log forgery path traversal parameter tampering and others in myriad programming languages Additionally developers can add their own questions and vulnerable code to the game in any programming language highlighting any vulnerabilities growing the game s scope as more users join http www gameofthacks com Laura Cassell and Alan Gauld s Python Projects Wrox Python trainers Laura Cassell and Alan Gauld targeted their new book Python Projects at the Python programmer with basic skills who is ready to start building real projects Programmers who Python know the Python syntax and lay of the land but who still may be Projects intimidated by larger more complex projects will find this book useful Python Projects provides a walk through of the basic setup for an application and the building and packaging for a library and explains in detail the functionalities related to the projects Topics include m
67. d memory provided by gpsd server 127 127 28 0 prefer fudge 127 127 28 0 timel 0 040 refid GPS KerneL mode PPS ref clock for the precise seconds server 127 127 22 0 106 OCTOBER 2014 WWW LINUXJOURNAL COM fudge 127 127 22 0 flag2 flags 1 refid PPS allow ntpd to serve time if GPS is OFF tos orphan 5 The 0 040 might need adjusting relative to your GPS but It s a sate bet The 127 127 22 0 is the NTPd reference to dev ppsO If your GPSd declares a dev pps to the kernel your real PPS signal might become dev pps1 The bottom line is try to load your PPS signal before starting GPSd Verify that NTPd has started and serves the time with ntpq ntpq p remote refid st t when poll reach delay offset jitter el SHM 0 GPS 01 13 64 377 0 000 50 870 0 886 oPPS 0 APPa 01l 12 64 377 0 000 1 419 0 128 You can see here that GPS is identified as the system peer by ntpd and PPS is also correctly recognized and valid 0 The PRU a Very Hot Topic The two Programmable Realtime Units of the BBB can work independently of the main CPU on I O ports AINs and PWM They are sophisticated enough to share memory with a CPU up to 300MB have a rich instruction set and can trigger or receive interrupts Recently some hard workers managed to make the use of the BBB PRUs more accessible And there is this great promising GSOC 2014 coming BeagleLogic https github com abhishek kakkar Beagle
68. de SS oe 70s oa ee an SS ce ae Se ae WWW LINUXJOURNAL COM OCTOBER 2014 99 FEATURE Accessing the I O Ports of the BeagleBone Black with Python If 68 is not here but UU Is printed the kernel already keeps hold of the ds1307 with a driver Recheck your kernel messages and try to unload the driver for the ds1307 with the following and then retry echo 0x68 gt sys class i2c adapter i2c 1 delete device rmmod rtc_ds130 7 If this is just instead of 68 recheck your wiring Add a DAC the MCP4725 on i2c The MCP4725 is a 12 bit digital analog converter allowing you to output a voltage trom a numerical value between O and 4095 2 1 Its EEPROM allows you to store a value in a register that becomes the default value as soon as the DAC is powered on When you want to drive a motor with it you then can store a default safe value in EEPROM and then make certain that when the power is restored your motor doesn t start at full speed The wiring is almost identical as for the ds1307 module take the 3 3V VDD P9_3 as VREF for the MCP4725 The MCP4725 address on i2c is Ox60 or 0x61 select it with the AO 100 OCTOBER 2014 WWW LINUXJOURNAL COM pin on the MCP4725 Thus you can use two MCP4725s on the same bus so with two i2c buses you easily can output four independent voltages from your BBB Write a Value to the MCP4725 To set a voltage ouput on the MCP4725 write to the i2c bus So for a
69. ded to try to put the Pi to work as a dedicated sump pit monitoring device Hopefully the Pi could send me SMS alerts if a problem arose while was away Since did not have a programming background started to look for an existing project could install on the Pi that could act as a sump pit monitor There are other projects that can monitor sump pump activity however it seemed that everything came across looked overly complicated or didn t have the features required needed something simple that monitored the water level in the sump n June 2013 we had the pit at regular intervals and sent me a text if there was a problem If it also could display pretty graphs of sump pit activity that could access easily that would be a bonus Although had written many scripts through the years at work never learned object oriented programming made the decision to learn Python and a few months later set myself to work on a monitoring system chose Python because it has an active community and many Raspberry Pi enthusiasts use It as their main scripting language The Raspberry Pi uses Raspbian Linux which is based on Debian so that already was familiar ground With these tools in hand and in true Linux and Raspberry Pi spirit decided to build my own and called it Raspi Sump Raspi Sump is a sump pit water level monitoring system written in Python It uses a Raspberry Pi and an HC SRO4 ultrasonic sensor
70. dentities and creates a list of nouns prompts users for their free association synonyms for each of the nouns then pushes out the original text again replacing each original noun with a substitute as suggested by the user To start how do you identity nouns First We ll Kill All the Nouns was going to grab the comprehensive dictionary from Princeton University s COLUMNS Wordnet program but closer examination reveals that it has more than 85 000 words and has all sorts of obscure alternative uses and so forth The end result is that although it s comprehensive it generates too many false hits So instead Desi Quintans has a simple word only list you can grab for our purpose here http www desiquintans com downloads nounlist txt It s in exactly the format needed too head nounlist txt aardvark abyssinian accelerator accordion account accountant acknowledgment acoustic acrylic act It seems like that would be the most difficult step but in fact It s Surprisingly easy given the almost infinite data store of the Internet Identifying Nouns in Prose The next step is rather easy given some prose break it down into individual words then test each word to identify which are nouns This is really the bulk of the program now WORK THE SHELL that we have a noun list for word in sed s punct g dream mtr A Z a z tr n do is the word a noun Let s
71. dup As in past years in this article describe books that were new to me during the past 12 months which means that might well mention some new ones or ignore others that simply didn t come to my attention My interests professionally and for this column generally are relevant to people involved in Web development using Open source technologies but admit to veering into other subjects occasionally And as have done for the last Tew years of this annual roundup have expanded my list of books also to include blogs podcasts and other resources that may be of interest to others in the Open Source community Programming Languages Python continues to grow in popularity and for good reason it s 32 OCTOBER 2014 WWW LINUXJOURNAL COM an elegant language that Is both powertul and easy to learn have been teaching a growing number of Python courses during the past few years to a variety of audiences aspiring Web developers companies interested in moving their automation and testing systems into an open source high level language and also people interested in learning basic programming techniques and ideas The best known book about Python Programming Python by veteran instructor Mark Lutz recently was released in its 4th edition by O Reilly ISBN 9780596158101 The book has been expanded and improved in many ways most importantly with additional information about Python 3 x Truth be told have yet
72. e I O pins until after the SYS_RESETn signal is HI 3 3V Pimp My BBB The Debian system When we received our BBB boards in September 2013 they were pre installed with the Angstrom distribution Thanks to the work of others who were also attached to Debian quickly was able to keep playing with my favorite Linux system on my fresh BBBs installed the images provided by eLinux but you also can Do not apply any voltages that are generated from external sources until the SYS_RESETn signal is HI If voltages are generated from the VDD_5V signal those supplies must not become active until after the SYS_RESETn signal is HI If you are applying signals from other boards into the expansion headers make sure you power up the board after you power up the BeagleBone Black or make the connections after power is applied on both boards Powering the processor via its I O pins can cause damage to the processor fetch an image from armhf http www armhf com boards beaglebone black wheezy Since March 2014 Debian Wheezy stable is an official system image available for the BeagleBone Black rev B and C For the latest images see http beagleboard org latest images You can choose to upgrade to testing or sid if you feel more adventurous in WWW LINUXJOURNAL COM OCTOBER 2014 85 order to enjoy more recent software See the Upgrading from Debian Stable to Debian Testing sidebar Upgrading from
73. e as pert already does add a few more functions that had a notrace attribute on them and feed this into a special linker that unpacks existing vmlinux throws away cold functions relocates the rest and here you have tiny vmlinux without recompilation But Andi pointed out that for networking code this wouldn t really work He objected How would you know you exercised all the corner cases in the TCP stack And you wouldn t want a remotely exploitable system because some important error handler is missing The discussion ended inconclusively But it does seem as though real patches and not linker hacks will be used to support all new hardware even the tiny hardware that s been coming out lately ZACK BROWN 18 OCTOBER 2014 WWW LINUXJOURNAL COM Do not hire a man who does your work for money but him who does it for love of it Henry David Thoreau When in doubt tell the truth Mark Twain Experience isa good teacher but she sends in terrific bills Minna Thomas Antrim Just the knowledge that a good book is awaiting one at the end of a long day makes that day happier Kathleen Norris Always be a little kinder than necessary James M Barrie t UPFRONT EdgeRouter Lite In the September 2014 issue mentioned my new router and gota lot of e mail messages asking about how well it works can say without hesitation it s the nicest router I
74. e Gadget Guy for LinuxJournal com and he has an interesting collection of vintage Garfield coffee mugs Don t let his silly hairdo fool you he s a pretty ordinary guy and can be reached via e mail at shawn linuxjournal com Or swing by the linuxjournal IRC channel on Freenode net LECLECEOUEEETTEECTETETCETETEETTE T Send comments or feedback via http www linuxjournal com contact or to ljeditor linuxjournal com WWW LINUXJOURNAL COM OCTOBER 2014 51 NEW PRODUCTS wt CAMBRIDGE 3 NIVERSITY FRISS Paragon Software Group and Cambridge University Press Cambridge English Pronouncing Dictionary English language learners and American Anglophiles practicing their imitation of James Bond will delight in the news that the Cambridge English Pronouncing Dictionary is now in app form This latest version of the dictionary the classic guide to accurate contemporary pronunciation for British and American English is published jointly by Cambridge University Press the world s oldest publisher and Paragon Software Group This dictionary app for Android iOS and Mac OS X users is based on the classic version of Daniel Jones guide to contemporary pronunciation for British and American English and is designed to meet the needs of English language learners striving to perfect their pronunciation of even the most challenging words such as though and hono u r personal names company names technology and
75. e open source InfraRecorder is at http infrarecorder org and the freeware ImgBurn Is at http www imgburn com Once they switch to Linux everything they need will be an apt get or yum away SHAWN POWERS WWW LINUXJOURNAL COM OCTOBER 2014 29 L EDITORS CHOICE EDITORS Android Candy Goodbye RDP Hello Chrome Remote Desktop CHOICE Controlling a remote computer is GUI Linux machine it s always a pain something you re all familiar with in the rear Whether that means RDP to your The folks at Google are trying to corporate Windows Server we make it a little easier with Chrome don t judge Apple Remote Desktop Remote Desktop It s a combination which is really VNC to your OS X of Chrome browser app and machine or VNC X11 etc into your native binary that runs on your Remote Assistance User to user screen sharing perfect for remote technical support Get started My Computers To enable remote connections to a different computer install Chrome Remote Desktop there and click Enable remote connections y You must enable remote connections if you want to use Chrome Remote Desktop to access this computer Enable remote connections 30 OCTOBER 2014 WWW LINUXJOURNAL COM client machines Once the demon is Installed you can access the computer remotely from anywhere including a really cool Android app The combination of available platforms is pretty impressive too
76. e ttyO4 and tell GPSd to listen to all network interfaces G START _DAEMON true GPSD_ OPTIONS G n DEVICES dev tty04 USBAUTO false GPSD_ SOCKET var run gpsd sock Then restart it etc init d gpsd stop etc init d gpsd start By now your GPS is available to all clients on your network and you can try to connect to GPSd with QGIS or OpencCPN for example but a rather simple solution is with gosmon On another machine with the gpsd clients package Installed launch gosmon tcp bbbO02 2947 And you should see a screen like the one shown in Figure 11 Connect to GPSd from Python The python gps package provides what you need but the dialog sequence with GPSd is not trivial wrote a little Python class GPSd_client see the gpsd_client py file on my GitHub page in order to be able to access my GPS like this ipython Python 2 7 8 default Jul 22 2014 20 56 07 Type copyright credits or License for more information In 1 from gpsd_ client import GPSd client In 2 gps GPSd_client bbb02 In 3 for gpsdata in gps print gpsdata GPS time u 2014 07 24T08 53 54 000Z Latitude 48 3938485 Longitude 4 505373 altitude 30 4 sog 0 051 cog 187 71 ept 0 005 mode 3 GPS time u 2014 07 24T08 53 55 000Z Latitude 48 393848 lLongitude 4 505373167 altitude 30 3 sog 0 067 cog 194 8 ept 0 005 mode 3 GPS time u 2014 07 24T08 53 56 000Z Latitude
77. ed to AT THE FORGE increase performance benchmarking and profiling to understand where the problem Is NumPy s arrays which are faster if more limited than Python s built in lists Cython which translates Python code into C and finally multiprocessing The book is relatively short at 108 pages but it does provide some of the most common techniques for increasing program speed At the same time think that some more basic techniques such as not using to iteratively build strings would have added something to the book The hottest language continues to be JavaScript if for no other reason than the very large number of people who have access to browsers be it on their computers or their mobile devices JavaScript s huge community has been pushing forward with a variety of techniques and libraries that make development easier Moreover JavaScript is now popular beyond the browser in such places as node js a server side framework that uses asynchronous JavaScript It is this first topic that Async JavaScript written by Trevor Burnham and published by the Pragmatic Programmers ISBN 978 1 937785 27 7 addresses Part of the difficulty that people have when working with JavaScript is its asynchronous nature You often set up a function to be WWW LINUXJOURNAL COM OCTOBER 2014 33 COLUMNS C AT THE FORGE executed later on when a particular even happens and it s frequently tough to remem
78. eep trying too so even if the network Is down for an extended time when it comes back up the SSH connection will be re established AutoSSH is available for just about every major distribution but it has to be installed on the computer inside the firewall because that s where the connection has to initiate from How do it is basically put something like this in my crontab to run on reboot autossh M 41000 f N R 0 0 0 0 2222 127 0 0 1 22 user remotehost Only two of the flags are for AutoSSH the others get handed off to SSH itself Basically the M 41000 establishes a monitor port for AutoSSH to use It s possible to use SSH s built in ability to monitor a connection but I ve had very bad luck with it Using AutoSSH s M flag seems to work the best It doesn t matter what port you select as long as it s not currently in use on either computer The next flag f just tells AutoSSH to run in the background and monitor the connection The rest 48 OCTOBER 2014 WWW LINUXJOURNAL COM of the line is similar to what showed typed above used to write complex bash scripts to check for connectivity and kill oft then restart SSH but using AutoSSH is much more efficient and reliable I ve been using it for years and it is rock solid The most I ve ever had to do is kill off defunct SSH connections on the public server if for some reason can t connect AutoSSH then happily creates a new connectio
79. eful to record a few different simple macros under different keys then record a new macro that just calls those other macros in a particular order Among other things this lets me change some of the shorter macros if need to without having to re record everything For the first example let s look at a more complete version of the BIND zone Tile used last time BIND data file for example com TTL 15m IN SOA example com root example com 2014081500 10800 1200 7200 7200 COLUMNS example com IN NS ns1 example com example com IN NS ns2 example com ns1 INA 10 9 0 5 ns2 IN A 10 9 0 6 worker1 INA 10 9 0 15 worker2 INA 10 9 0 16 worker3 INA 10 9 0 17 worker50 IN A 10 9 0 64 In this example let s say have 15 zone files for different zones but want to make the same set of edits to all of them want to change the TTL in the file to be 10 minutes and need to change the contact info for the domain from root domain to dnsadmin domain also need to Increment the serial number 2014081500 in the zone file and need to change the name server IPs all to point to a new set of name servers at 10 1 0 250 and 10 1 0 251 and finally want to add 50 more workers to each zone file Although imagine could build all of this into a single big macro for me it makes sense to split up the steps into at least four macros that already have pre assigned letters to E Macro t will ch
80. erform these same steps on a number of files might as well capture all those commands in a new macro I ll assign to c To do that just type qc to enter macro mode assigned to the c key then type t s n50 w to perform all of the previously recorded macros Finally type q to exit macro mode The complete set of keystrokes is qc t s n50 wg to assign all of the above sets of keystrokes to a single macro Now when open the next HACK AND file can just type c to perform the complete list of steps Now besides saving a few keystrokes there are other good reasons to nest macros in this way Because saved each logical step as its own macro can tweak or modity any of the above macros independently save the new macro to the same key and all of the other macros including the final combo macro can stay the same Let s say that after recorded all of these macros realized got the IP address for the name servers wrong All would have to do Is record a new macro assigned to the same n key and once was done still could use c to make the complete set of changes to a Tile hope you find these examples useful and that the next time you have to perform a series of mundane edits to many text files you ll save some keystrokes with vim macros E Kyle Rankin is a Sr Systems Administrator in the San Francisco Bay Area and the author of a number of books including he Official Ubuntu Server Book Knoppix
81. he BBB as Time Server from a GPS What if you put together the interface to your GPS the NTP server of your Linux machine equipped with an RTC and the accuracy provided with the PPS signal You can build an NTP server for other CPUs in your network and with good accuracy as soon as the GPS Is aligned Keep in mind that you need a so Samuel sook topt bbh0212947 NMEQOLES gt OO golly Time 2014 0 24705321 Lat amuel W ii 2inux ournal an 1 ar l af m l good RTC wired to the BBB for a real NTP server so choose one like the Adafruit Chronodot http www adafruit com products 255 rather than the simple DS1307 GPSd Now that you know how to handle a serial port you can install the GPSd software GPSd connects to a local GPS as the one we wired to UART4 and serves GPS data to clients apt get install gpsd python gps gpsd clients dol N bons 4 a0 13 153 W Cooked PYT GPGGA GPGLL GPYTG GPZIA GPRAC Senbences PRH a oe oe Latitude Longitude peed Course E H E Pa 0 06 196 09 r 7 Jog fei 0 1 2 4 a 6 Fi 8 9 10 11 GS OP200 Od2154 00 24 07 2 304 014 00 006A Figure 11 A Session with gosmon 104 OCTOBER 2014 WWW LINUXJOURNAL COM baat 0040 41944 Goelag H dors EER 00450 31953 1 2 6 Bo z Sats q weOd xO Edit the etc detault gpsd cont Tile modity it to connect to your serial port her
82. his issue of Linux Journal of course check out his column Dave Taylor begins a new adventure this time attempting to parse the written word and grammar with scripts It s always fascinating to see tasks that are simple for humans attempted by programs and logic Dave s column is more than just instructive it will force you to think as well Speaking of thinking the title of Kyle Rankin s column this month will make you think hard Return of the Mac seems like the exact opposite of what Kyle would write about And of course he doesn t talk about an Apple product won t give it away but don t worry Kyle hasn t given up the command line for the GUI world of Apple in fact quite the opposite put on my grey hat this month and talk a little bit about SSH Hacking is a word that is used to describe far too many things most of which think are more accurately described as Using Things Like They Were Made To Be Used but that s not as catchy for a movie title Firewalls are important security tools for any network but it s important to realize that firewalls can t be your only defense against access This month show you why Do hack the firewall don t think so but for someone unfamiliar with SSH tunneling it sure looks like it Al Audet shows how to embed Linux into a hole in the ground this month More specifically he explains how he uses a Raspberry Pi device to monitor
83. iOS and Renewing your subscription e mail address for issue delivery pi invoice viewing your account det subscription inquiries can be on line http www linuxjot E mail us at subs linuxjour us via postal mail at Linux 980985 Houston TX 77098 L remember to include your cc and to the digital archive T digital archive at any time http www linuxjournal co LETTERS TO THE EDITOR We letters and encourage you 1 at http www linuxjournal com cont mail them to Linux Journal PO Box 9 Houston TX 77098 USA Let edited for space and clarity WRITING FOR US We always for contributed articles tuto real world stories for the ma An author s guide a list due dates can be found or http www linuxjournal con FREE e NEWSLETTERS Lir editors publish newsletters on k a weekly and monthly basi late breaking news technical ti tricks an inside look at upcoming and links to in depth stories fe ul http www linuxjournal for free today http www linuxj enewsletters ADVERTISING Linux Journal is resource for readers and ad Request a media kit view editorial calendar and adve or learn more about other adve and marketing opportunities by us on line http ww linuxjour advertising Contact us directly information ads linuxjour 1 713 344 1956 ext 2 GEEK GUIDE slow Down to Speed Up GEEK GUIDES DevOps is one of the newest and largest movements in Information Technology in the past few
84. ia and technology that we use nowadays has precedents in previous cultures His funny and interesting book is sure to give you some perspective on Facebook and LinkedIn among other things Another great book that came out this year is How Not to Be Wrong The Power of Mathematical Thinking COLUMNS by Jordan Ellenberg Ellenberg is a mathematics professor and he tries to show in this book how mathematical thinking can help you make useful decisions He starts the book by pointing out that mathematics isn t what you learned in elementary and high school and it succeeds In having very few equations in the book Rather his point is to show how it s a perspective on life that can help you make decisions or persuade others To his credit the author also includes a number of examples of where mathematics cannot really provide a clear cut answer such as most surprisingly in deciding election results As readers of this column know have traveled to China several times in the past few years to teach Ruby and Python programming classes And I ve become something of an aficionado of China related books written by reporters who were there Evan Osnos who was the New Yorker s correspondent in China for several years published a book this year titled Age of Ambition Chasing Fortune Truth and Faith in the New China that tries to make sense of the political and social changes happening in China Along the same lines
85. ilize CacheGuard OS as an appliance or turn their own hardware into a powerful Web Gateway Appliance CacheGuard OS integrates numerous Web security and optimization technologies in a single functional network device Technologies like proxy IP firewall bandwidth shaping caching HTTP compression URL filtering Web application firewall and Web malware filtering are all integrated into a unique operating system http www cacheguard com Please send information about releases of Linux related products to newproducts linuxjournal com or New Products c o Linux Journal PO Box 980985 Houston TX 77098 Submissions are edited for length and content WWW LINUXJOURNAL COM OCTOBER 2014 55 How to set up a sump pump monitor with an ultrasonic sound sensor Raspberry Pi and Python unfortunate luck of a basement flood caused by a tripped electrical breaker connected to our sump pump There are so many things that can go wrong with a sump pump You always are on guard for power outages blown breakers sump pump failures clogged pipes and all manner of issues that can arise which ultimately can end with a flooded basement needed a way to alert me of issues when I was not at home Audible alarms are fairly cheap and are great when you are physically in the house They fail miserably when you are ten miles away at work had a Raspberry Pi that had tinkered with periodically but for which I never had a real purpose deci
86. imulation environment for cyber physical systems SystemModeler enables users to draw on a large selection of built in and expandable modeling libraries to build industrial strength multidomain models of a complete system Wolfram is also well known for the complementary Mathematica application which provides a Tully integrated environment for analyzing understanding and quickly iterating system designs The new SystemModeler 4 vastly expands support tor modeling libraries adds standardized deployment of models to other simulation tools and deepens integration with Mathematica Other key new features include a library store with veritied model libraries improved modeling features model creation support from Mathematica as well as improved worktlow in the integration with Mathematica a new documentation center and support for our beloved Linux OS http Awww wolfram com CacheGuard Technologies Ltd s oo CacheGuard OS ne CacheGuard Technologies Ltd s motto is Web security made affordable The company puts its motto into action with products x like CacheGuard OS an integrated security solution designed HW Appliance to manage Web traffic that is based on a custom hardened version of Linux The latest next generation release is CacheGuard OS NG v1 The company calls CacheGuard OS a powerful turn key solution that allows companies to protect and optimize Web traffic traversing their Web infrastructure Customers can ut
87. infrastructure to access environment data stored in serial flashes NVRAM NAND datatlash MMC and even UBI volumes See the U Boot documentation for more information on how to use these CONFIG options Since the default environment size has to be minimized most of the environment variables are stored here Certain storage technologies like raw NAND flashes are inherently unreliable To combat such possibilities including power failure and for robustness in general you also can configure a redundant user environment You can configure the location and size of this duplicate environment data as well in your board s contig Saving Environment Out of the two default environments default and user only the user is writable So whenever you modity a variable and issue a saveenv command that variable ends up in the user environment When you do a saveenv U Boot does the following m Sorts the list of current environment variables E Converts them to a linearized list of strings E Computes CRC over this data and burns the env back at its fixed location in storage Creating a Pre Built User Environment U Boot provides a utility named mkenvimage that can be used to generate an environment blob suitable to be flashed mkenvimage needs at least two Inputs to create the blob WWW LINUXJOURNAL COM OCTOBER 2014 73 FEATURE U Boot Environment Variables 1 Environment variables in a text file only one env
88. ion you just have to download and wget c https raw github com RobertCNelson tools master pkgs dtc sh chmod x dtc sh dtc sh The script will fetch the tools on line so if your BBB is not connected you can compile your dtbo file from another Linux machine Danger the dtc program available in Debian Wheezy is not able to write a dynamically loadable dtbo file It may lack the option depending on the system you installed Check the output of dtc h and whether the is present See the Fetching a Good dtc sidebar The dtbo file produced will then be loaded to the kernel cp GPS PPS P9 23 Q0A0 dtbo 1lib firmware echo GPS PPS P9 23 gt sys devices bone capemgr slots To verity that the PPS is seen correctly by the Linux kernel you need the pps tools package installed ppstest dev pps0 trying PPS source dev pps0 found PPS source dev pps0 ok found 1 source s now start fetching data source 0 assert 1391436014 956450656 sequence 202 clear 000000000 sequence 0 source 0 assert 1391436015 956485865 sequence 203 clear 000000000 sequence 0 source 0 assert 1391436016 956517240 sequence 204 clear 0 000000000 sequence 0 source assert 1391436017 956552407 sequence 205 clear 000000000 sequence 0 Ctrl C to end You see here a signal received at 1Hz with a timestamp jitter less than 1ms WWW LINUXJOURNAL COM OCTOBE
89. iptions E MAIL subs linuxjournal com URL www linuxjournal com subscribe MAIL PO Box 980985 Houston TX 77098 USA LINUX is a registered trademark of Linus Torvalds drupatize me Instant Access to Premium Online Drupal Training Instant access to hundreds of hours of Drupal training with new videos added every week Learn from industry experts with real world experience building high profile sites Learnon the go wherever you are with apps for tOS Android amp Roku J We also offer group accounts Give your whole team access at a discounted rate Learn about our latest video releases and offers first by following us on Facebook and Twitter drupalizeme Go to http drupalize me and get Drupalized today K module x macromaker js x jquery insertArCaret js r 3 4 Usage obj insertAtCursor text 5 obj a textarea or textfield 6 text a string to insert 7 j 8 fn extend Jg insertAtCaret function myValue 190 return this each function 11 If target element is hidden don t do it 12 if this isC hidden C parents hidde 13 return 14 i 15 if Cdocument selection 16 this fa 17 sel d 18 sel tex drupalize me this fe Learn Drupal amp jQuery n else if The Super Convenient Waa cz var sta OVER BO WIDEDS 6 67 HOURS OF Cem TAA var enc 24 var scr 25 this ve 26 this fe High bgp tisy ind p
90. is saying Hi remote THE OPEN SOURCE CLASSROOM server I m stuck behind a firewall Will you listen on port 2222 for anyone trying to connect and if they do please forward the traffic to me on my port 22 The command can get creepier too In my example just forwarded traffic to the public port 2222 to the internal port 22 behind the firewall But if you were to change the command like this ssh N R 0 0 0 0 3389 192 168 1 5 3389 user remotehost You ve now created a public access tunnel directly to the Windows RDP server on 192 168 1 5 behind the firewall Anyone on the Internet who connects their RDP client to the remote host s IP address will get the RDP login screen from 192 168 1 5 Freaked out yet One of the problems with this setup is the relative instability of the Internet If the SSH connection is severed the tunnel collapses and you no longer can reach the computer inside the firewall Thankfully there s a really great tool to help with that too AutoSSH AutoSSH Having a diabolical tunnel to an internal network across the globe Is only awesome until it stops working WWW LINUXJOURNAL COM OCTOBER 2014 47 COLUMNS _ THE OPEN SOURCE CLASSROOM SSH is a finicky protocol so the Smallest blip over the Internet can cause the connection to fail If you launch the SSH command with AutoSSH however it will monitor your connection and restart it if things go wrong AutoSSH will k
91. k There is and will be a lot of work done and money spent on this issue Operators are pushing vendors for open source There is OpenDaylight as well for SDN The vendors are big ones such as Ericsson Huawel ALU Oracle Cisco Nokia Microsoft and HP Some other vendors are AT amp T Orange and TIM Those are the biggest players around You are the Linux magazine yet see almost nothing on these issues This disappoints me Personally would like to see not only NASA s open source tools but also such big enterprise issues ON Open source and Linux Linux is a serious thing that runs the Internet and many serious applications on the enterprise level would like to see these improvements in your magazine Umit Kaan Sonal We look for content that interests our users along with new technology we think deserves to be noted Getting feedback like yours is the best way for us to know what readers want so we ll keep our eyes open Thanks Shawn Powers WRITE LJ A LETTER We love hearing from our readers Please send us your comments and feedback via http www linuxjournal com contact PHOTO OF THE MONTH Remember send your Linux related photos to ljeditor linuxjournal com 14 OCTOBER 2014 WWW LINUXJOURNAL COM ioe A 4 7 i y y N Pg j A i A a A i i q mI 7 7 T f k y b i J i J 0 U R N ht epub mobi and an on line digite as well as apps for
92. lability Also noteworthy is the real time notification of problems leading to increased Linux and UNIX service availability regardless of the hardware platform on which Linux or UNIX resides http Awww aesclever com See Paul Schuytema s waaa The Web Wargame Toolkit lt 2 Mercury Learning amp Information Paul Schuytema s new book The Web Wargame Toolkit walks readers through the process of crafting an old school turn based wargame in PHP utilizing the Codelgniter application framework More generally this is a soup to nuts how to book for those interested in crafting Web game applications utilizing a basic LAMP system The wargame project serves as an exciting context for PHP programmers looking to gain more in depth application coding experience Those with an interest in game development will learn the coding skills to support design decisions as they create the game project The book assumes at least a beginning level of PHP coding experience though no previous Codelgniter or game development experience is required Other features of the book DVD set include full database design for game data structures a flexible game map system a complete overview of a simple CRUD system and complete modifiable source code for the game http www merclearning com 54 OCTOBER 2014 WWW LINUXJOURNAL COM NEW PRODUCTS Wolfram SystemModeler The updated Wolfram SystemModeler 4 is an easy to use next generation modeling and s
93. ld do it with a keyboard and display or the serial access instead 88 OCTOBER 2014 WWW LINUXJOURNAL COM date saved when the system halted To DHCP or Not to DHCP If your network hosts a DHCP server you are fine otherwise you can configure your network card static in order to avoid a big DHCP timeout when you boot your BBB with the Ethernet cable plugged in See the Configuring the Network Card Static sidebar A Life Line Serial Debug More often than not the boards are in a place where we can t have a keyboard and display attached to them We can work remotely by SSH but if something goes wrong we need to access the serial debug interface on the board The serial interface available through the USB connection to the board is not ready when you boot with U Boot you can t see the kernel starting or intervene That s why we use the serial debug provided by the J1 connector on the board referred to as ttyOO by the system As a side note this serial line can be made available via Ethernet with a cheap RS232IP converter if remote boot monitoring is needed Before connecting our BBB ona PC via this serial line we need a TTLRS232 converter See some serial debug references on eLinux at http elinux org Beagleboard BeagleBone_Black_Serial You can purchase a PL2303HX USB to RS232 TTL auto converter module they are very cheap Just make sure the end of the cable is made of jumper wires and n
94. le satellite view For some of these views you may notice a small down arrow in one of the top corners Clicking this icon gives you an appropriate drop down list of options For example clicking the down arrow in the map view gives you a list of items such as detaching the module or configuring it Figure 2 The map view offers a map of the Earth with a series of satellites and their footprints on the Earth When you hover over one of the satellites you will see an information box with the satellite s detailed location The single satellite view provides WWW LINUXJOURNAL COM OCTOBER 2014 23 t UPFRONT Module Name Amateur Ground Station DEFAULT F F Y B Satellites N Hint Double click on any satellite 7 to move it to the other box Group All satellites e Available Satellites Selected Satellites 2011 0094 AO 27 AAU CUBESAT AO 51 AAUSAF II FO 29 ABRIXAS gt Ho s8 ABS 5 AGILA 2 Iss ABS 1 LMI 1 so so ABS 1A KOREASAT 2 50 67 ABS 7 KOREASAT 3 Properties Cancel OK Figure 3 You can set the configuration details for the map view here even more detail about one specific satellite You can select which satellite is being displayed by clicking on the down arrow in the view The polar view provides an overhead look
95. look if z grep E word nounlist then nouns nouns word fi done The for loop is a bit complicated but it s removing all punctuation from the input translating uppercase to lowercase and then converting each Space into a carriage return The result can be shown most easily by example Let s say that we had this as input I ve never seen a blue chipmunk Running it through the sed tr tr filter produces this ive never seen a blue chipmunk That s easy enough and now that we can separate out each word from the input it s easy to search the noun list to see if any match Again it s WWW LINUXJOURNAL COM OCTOBER 2014 39 COLUMNS WORK THE SHELL a bit complex because we need to ensure that we aren t getting embedded matches for example matching the noun acoustic for the slang word stic That s done by rooting the search as a regular expression is at the beginning of the line and is the end of the line hence the regular expression word where the use of the optional notation just delimits exactly what the variable name is to the shell With some debugging code included here s our first draft of this entire script bin sh dreamer script to help interpret dreams does this by asking users to describe their most recent dream then prompts them to free associate words for each of the nouns in their original descrip
96. managing console changes splash images and so on Type and Access Control of Environment Variables There are certain environment variables that you want to use but do not want to do casual modifications For example say you have an environment variable serial you definitely want this variable to be read only and you want automatic rejection of any 78 OCTOBER 2014 WWW LINUXJOURNAL COM attempt to change it Another such example is the MAC address of the device Again you want to keep that variable as read only or at worst write once U Boot supports different access modifiers any read only write once and change default Figure 5 The U Boot hashtable representation of environment variables has amember int flags Figure 5 The member flags is used to keep a bitmap specifying the access permission associated with variable So whenever any modification attempt is done on variable it must comply with the access permission otherwise U Boot will reject the changes Another problem faced by users is the basic sanity check of environment variable type Since the linearized form of environment keeps only strings U Boot needs to make sure that it can do some kind of type check before assigning a value to a variable To address this issue U Boot makes use of some predetined types such as string Deepthought gt setenv foo bar Deepthought gt setenv flags foo sr Deepthought gt setenv foo bar ip Error C
97. n and I m back in business What Good Is It personally use this sort of setup to access Internal servers that aren t accessible directly from the Internet don t like to open ports directly into internal servers if possible so if can grant myself access to multiple internal servers by SSH ing to a remote unrelated IP on a random port feel a little better about It also use this sort of setup to expose multiple Web servers trom inside a network to the outside Figure 1 shows the basic premise The command looks similar to the example above but with multiple R flags autossh M 41000 f N R 0 0 0 0 8001 192 168 1 10 80 R 0 0 0 0 8002 192 168 1 20 80 user remotehost To note that s all on one line COLUMNS THE OPEN SOURCE CLASSROOM host1 example com host2 example com Taani as INEL Response comes from here through tunnel Internet User 7 SSH Tunnel Internal N internal Worksation z host2 Figure 1 Although there s a lot going on behind the scenes an end user accessing the virtual hosts on the left just sees a Web server just used the backslash so it formats better Basically by using multiple SSH reverse tunnels the R flags internal Web servers are accessible by pointing the browser to http remotehost 8001 http remotehost 8002 and so on then use a reverse proxy see my column in the August 2013 Issue for details to
98. n inant scrwes tsi pat ramy vihen Leert free marma d EJAT are pet acrwes fe the eae Laidet Do b WYA Drupal ridens Kew vidros ary ag Current_Issue tar gz Linux Inside Linux Inside inux inside Linux inside every single one of us has Linux inside Sung to the tune of Devil Inside by INXS you re welcome for the ear worm can t get it out of my head either In the world of embedded systems systems on chip and single purpose hardware solutions It s easier to list the products that don t have Linux as their operating system This month we focus on putting Linux into tiny places and that means everything from the tiniest Android Wear watch to the ubiquitous Raspberry Pi As Linux users we ve been sneaking open source into server rooms for decades Now we get to sneak it in everywhere This issue starts with Reuven M Lerner discussing the books he s embedded into his bookshelf this year Month after month Reuven gives us incredible tips techniques and training VIDEO Shawn Powers runs through the latest issue 8 OCTOBER 2014 WWW LINUXJOURNAL COM SHAWN POWERS for programmers and neophytes like myself Now we get a glimpse at some of the books he uses for learning himself Whether you want advice on language books database books or even some information on freelancing Reuven shares his stash If you re looking for your next book to read after t
99. name value string on each line 2 The size of the environment blob in bytes remember this must comply with the CONFIG ENV SIZE you have defined in your board s contig For example if my env data file is called my_env_data txt and the size of my desired env blob is 16384 16 KiB would use the following command tools mkenvimage s 16384 o env_blob my_env_data txt You can see the dump of the env blob using the od command od t x1c env_blob 0000000 Od d2 49 96 62 61 75 64 72 61 74 65 3d 31 31 35 W322 I 226 b a wu d re 0000020 32 30 30 00 62 6f 6f 74 64 65 6c 61 79 3d 31 30 0000040 00 6c 6f 61 64 5f 61 64 64 72 3d 30 78 34 30 30 0000060 30 30 30 30 30 00 00 00 00 00 00 00 00 00 00 00 0000100 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0040000 74 OCTOBER 2014 WWW LINUXJOURNAL COM This environment data blob must be flashed at the predefined offset in the storage device You can use U Boot Linux or any other flasher to burn this blob Relocation of Environment Data to RAM During an early boot when U Boot has not relocated to RAM it uses the linearized form of environment data as shown in Figure 1 But once U Boot has relocated to RAM this linearized form is no longer used Instead U Boot imports all such env data stored from persistent storage into a RAM resident hashtable If the user supplied environment is good that is the CRC Is okay it is imported from Flash to RAM
100. nd performed with minimal downtime Join this webinar to hear from top IDC analyst Richard Villars about the path you can start taking now to enable your organization to get the benefits of turning data into actionable insights with exciting x86 technology gt http Inxjr ni modsap WHITE PAPERS Ny White Paper JBoss Enterprise Application Platform for OpenShift Enterprise Sponsor DLT Solutions Red Hat s JBoss Enterprise Application Platform for OpenShift Enterprise offering provides IT organizations with a simple and straightforward way to deploy and manage Java applications This optional OpenShift Enterprise component further extends the developer and manageability benefits inherent in JBoss Enterprise Application Platform for on premise cloud environments Unlike other multi product offerings this is not a bundling of two separate products JBoss Enterprise Middleware has been hosted on the OpenShift public offering for more than 18 months And many capabilities and features of JBoss Enterprise Application Platform 6 and JBoss Developer Studio 5 which is also included in this offering are based upon that experience This real world understanding of how application servers operate and function in cloud environments is now available in this single on premise offering JBoss Enterprise Application Platform for OpenShift Enterprise for enterprises looking for cloud benefits within their own datacenters gt http Inxjr nl jboss
101. ng for the Tree association of each identified noun Let s run it to see what mean sh dreamer sh Welcome to Dreamer To start please describe in a few sentences the dream you d like to explore End with DONE in all caps on its own line I was sitting in a tree house in the middle of an ancient forest and an owl was staring at me It asked who and I woke up in a cold sweat DONE Okay To confirm your dream was about I was sitting in a tree house in the middle of an ancient forest and an owl was staring at me It asked who and I woke up in a cold sweat Hmm okay I have identified the following words as nouns tree house middle forest owl cold Are you ready to do some free association Let s begin What comes to mind when I say tree What comes to mind when I say house What comes to mind when I say middle What comes to mind when I say forest What comes to mind when I say owl What comes to mind when I say cold As is immediately obvious the free association section at the end and the subsequent reassembly of the prose with the new Tree association words or phrases is still to come But that s a project for next month Meanwhile keep a dream journal and soon you ll be ready to interpret it thanks to the Linux shell or something like that m Dave Taylor has been hacking shell scripts for more than 30 years Really He s the author of the popular Wicked Cool Shell Scripts and can be found
102. nitrd high 90000000 load_addr 40000000 phrase The quick brown fox jumps over the lazy dog root Deepthought c Modify Environment of U Boot using command line or text file input Figure 10 My Configuration File the environment data blob Figure from the beginning of Flash and had 10 shows my configuration file a size of Ox40000 The size of each kept my environment in an SPI Flash sector of my Flash is 0x10000 This which appeared as dev mtd0O to my is all the information needed to kernel My environment blob was provide in order for the environment configured at an offset of Ox80000 manipulation utilities to work 80 OCTOBER 2014 WWW LINUXJOURNAL COM As soon as keyed in the command fw _printenv could see the variables that saved in the U Boot user environment appearing on my console You also can set the environment variables using fw setenv As shown in Figure 10 make use of a text Tile list txt containing the variables want to set The format is simple The first whitespace after a name acts as a delimiter and the characters until the end of line thereafter are considered the value for the key You can verity that the variables have been set by executing fw_printenv These variables now would be visible from U Boot as well Restoring the Default Environment Sometimes after a lot of environment variable changes you can corrupt the state To restore sanity and get the original values of
103. nt on change foo const char name const char value enum env_op op int flags printf callback handler on change foo invoked for variable Switch op case env_op create case env_op overwrite printf foo variable modified n break case env op delete printf foo variable deleted n break default break return 0 U_BOOT ENV CALLBACK foo h on change foo s n name Figure 6 Code a handler you want to call for an environment variable WWW LINUXJOURNAL COM OCTOBER 2014 77 FEATURE U Boot Environment Variables Deepthought gt setenv foo bar De pthought setenv callbacks foo fo0o h Deepthought gt setenv foo bar callback_handler on_change_foo invoked for variable foo foo variable modified Deepthought gt Figure 7 Associate the callback handler with the environment variable by setting an environment variable callbacks Here any modification of foo would invoke on_change_foo created a new environment variable Callbacks which is a standard U Boot system variable to make such associations have deployed a handler named foo_h for the environment variable foo Once this registration is done whenever you do some modification to variable foo the function on_change_foo would be invoked You now can deliver your reaction to different types of actions env_op create env_op overwrite or env_op_ delete U Boot already deploys similar handlers for
104. nterface for Raspi Sump on the Pi dike a home router E A GSM module component to use the cellular network for alerts instead of the Internet m A configuration file to store variables as opposed to within the script mM Package management for installation of Raspi Sump A sump pit monitor is just one tool you can use to help avoid a flooded basement It s not a replacement for a complete strategy that includes a backup pump on a separate electrical breaker A gas powered electrical generator is also essential for extended power outages Also kept my cheap Home Depot audible alarm A text alert at two in the morning is useless if am sound asleep want a full out screech to wake me up welcome all feedback on this project am not a professional programmer and am sure that can substantially improve the code or add useful features that have not even considered Although it s not perfect now have a system that works and gives me extra peace of mind while am away If you are looking for a similar solution hope you can use modity and improve Resources Raspi Sump to suit your needs If you do would love to hear from you Acknowledgement Special thanks to Ron Hiller GitHub user rhiller for tirelessly answering my questions about voltage dividers and his own sump pump monitor called pl distance https github com rhiller pi distance Al Audet lives in Timmins Ontario with
105. ntials and get it down to 100K per application competitive with Adam Dunkel s LwIP Lightweight IP project Andi posted some patches to create three available options for the networking stack a full system with all current features a partial system that supported regular users but not servers or a minimal networking system for the special userland on WWW LINUXJOURNAL COM OCTOBER 2014 17 t UPFRONT deeply embedded systems The minimal system he said would remove rtnetlink ioctl only remove ethtool raw sockets This seemed extreme to Richard Weinberger who said that on such a minimal system even the ps command wouldn t work Tom Zanussi on the other hand said that the microYocto Linux distribution ran okay with Andi s patches and had decent workarounds to keep ps working properly But he added that microYocto was very much a work in progress with a lot of rough edges but it is a Tully functional system on real hardware Alexei Starovoitov felt that trying to support such a minimal system would only create contig options that led to a hacky work in progress rough edged system He said that if the goal was to create a half functional system that was just very very small the same thing could be accomplished with linker hacks Simply compile kernel as is Most functions have a stub for mcount already Use it to track whether the kernel function was called or not Collect this data in userspac
106. ode with our cute and clever puppets So said I d like to interview them and 110 OCTOBER 2014 WWW LINUXJOURNAL COM here s how it went DS What got you going on this JN Growing up we wanted to be making creative media such as games videos animations etc but in the days before the Internet training was either difficult or expensive to find especially in small town Utah We figured things out on our own through trial and error visits to the library and countless hours watching PBS The Hello World Program is the show we wish we watched as kids DS Do you or your brother have kids yourselves JN Neither of us have kids but we are both kids at heart DS How long have you been doing it JN We started kicking around ideas for an educational Web series in January 2012 Then we sat on our hands for a few months We published our first video What Is a Robot in May of that year Since then The Hello World Program has significantly evolved We introduced several new characters and expanded our scope to include Web development and programming DS Where in rural Utah are you A side thing I love Utah and have shot it a lot from the air https www flickr com search text Utah amp user_id 52614599 40N00 amp sort interestingness desc JN Our home is Richfield the gateway to adventure in Southern Utah DS Cool I shot your house from the sky just this past May 4th
107. of my favorites in Linux Journal However while reading the August 2014 issue thought don t re invent the wheel In astronomy getting the time interval in days and fractions WWW LINUXJOURNAL COM OCTOBER 2014 11 LETTERS thereof between any dates is a daily bread and butter issue The solution is the Julian Date a consecutive count of days from centuries ago into the future It is a relatively simple algorithm although not intuitive See for example http aa usno navy mil faq docs JD_Formula php Yes the algorithm is originally coded up in FORTRAN what else was there in the science world some decades ago and we still use It A conversion to a shell script or any other programming language should be easy Norbert Zacharias Dave Taylor responds Holy cow that s awesome stuff Norbert haven t dabbled in FORTRAN since the job had while was an undergrad at UCSD back in the early 1980s As it happens really enjoyed FORTRAN and enjoyed reading the code too How that formula works however is a bit puzzling to me as there are some rather mysterious constants that don t seem like they should work Still it d be easy enough to recode as a shell script in fact the FORTRAN code is almost workable as is with just a few tweaks My only comment the lack of error checking makes me get 12 OCTOBER 2014 WWW LINUXJOURNAL COM a bit anxious with such complicated formulae in the
108. ogramming 9 Boot i the Arduino on a Spr te fewer For more information about advertising opportunities within Linux Journal iPhone iPad and Android apps contact John Grogan at 1 713 344 1956 x2 or ads linuxjournal com t UPFRONT Non Linux FOSS Remember was chatting with a Windows using friend recently and he wanted to try Linux on one of his older computers always like those sorts of conversations and so kept chatting walking him through setting up Unetbootin to create a USB Installer and so on and so on Unfortunately he wasn t able to get the USB drive to boot Since we were half a country apart couldn t troubleshoot locally so we moved on to burning a CD DVD My first instinct was to have him download the incredible InfraRecorder Untortunately there seems to be a malware infected version of InfraRecorder going around and of course that s the download link he found So be sure to send folks directly to http infrarecorder org to download it Alternatively I m a big fan of the free but not Ttree program ImgBurn as well It s not open source but it is freeware and it has a very simple interface Either way you go be sure to warn potential Linux converts Burning ISOs Image courtesy of http www visualpharm com about the malware masquerading as open source software Remember to send people directly to the Web site rather than having them google for it Th
109. on Marti dmarti linuxjournal com Michael Baxter mab cruzio com Reuven Lerner reuven lerner co l Mick Bauer mick visi com Kyle Rankin greenfly net Bill Childers bill childers linuxjournal com Contributing Editors Ibrahim Haddad Robert Love Zack Brown Dave Phillips e Marco Fioretti e Ludovic Marcotte Paul Barry e Paul McKenney Dave Taylor Dirk Elmendorf e Justin Ryan e Adam Monsen President Publisher Associate Publisher Director of Digital Experience Accountant Carlie Fairchild publisher linuxjournal com Mark Irgang mark linuxjournal com John Grogan john linuxjournal com Katherine Druckman webmistress linuxjournal com Candy Beauchamp acct linuxjournal com Linux Journal is published by and is a registered trade name of Belltown Media Inc PO Box 980985 Houston TX 77098 USA Editorial Advisory Panel Brad Abram Baillio e Nick Baronian Hari Boukis e Steve Case Kalyana Krishna Chadalavada e Brian Conner Caleb S Cullen Keir Davis e Michael Eager Nick Faltys Dennis Franklin Frey Victor Gregorio Philip Jacob Jay Kruizenga David A Lane Steve Marquez Dave McAllister e Carson McDonald Craig Oda Jeffrey D Parent Charnell Pugsley e Thomas Quinlan Mike Roberts Kristin Shoemaker e Chris D Stark Patrick Swartz James Walker Advertising E MAIL ads linuxjournal com URL www linuxjournal com advertising PHONE 1 713 344 1956 ext 2 Subscr
110. on Twitter as Davelaylor and more generally at his tech site http www AskDavelaylor com PEE Send comments or feedback via http www linuxjournal com contact or to Ijeditor linuxjournal com WWW LINUXJOURNAL COM OCTOBER 2014 41 COLUMNS HACK AND Return of the Mac KYLE RANKIN Save yourself keystrokes by building a library of vim macros to automate mundane text editing tasks In my July 2014 column talked about vim macro basics In that article described how to record a custom macro assign It to a key and then use it to make automated edits to a BIND zone also teased that would cover more advanced uses of macros like nested macros in a future issue took a brief detour to cover a Tew different topics but now I m back on topic and in this article discuss more complicated uses for macros like using BIND zone files for macro examples because It s the file most often use macros in myself Because multiple people often edit zone files they may not all have the same formatting Plus the top of a zone file generally has a different multi line format compared to the rest of the file In my July 2014 article talked about how to add 50 sequential A records in a zone file using a single macro but when have to pertorm 42 OCTOBER 2014 WWW LINUXJOURNAL COM more complicated edits or if have to perform edits selectively in some files but not others I ve found it us
111. onment of your board Apart from the standard variables used across boards you may want to add certain environment variables that are specific to your board or that just are convenient for you You may for instance want to embed the revision number of the board into this environment You could do that by defining all of these variables in a macro WWW LINUXJOURNAL COM OCTOBER 2014 71 FEATURE U Boot Environment Variables Include configs lt YOUR_BOARD gt config define CONFIG BOOTARGS define CONFIG IPADDR define CONFIG GATEWAYIP define CONFIG ETHADDR define CONFIG SERVERIP console ttyAMAO0 115200 Se sste A avi 192 1687071 DE AD BE EF 01 01 192 16802 Figure 3 System variables defined in your board s config become part of the default environment called CONFIG EXTRA ENV SETTINGS in your board s config Tile define CONFIG EXTRA _ENV_SETTINGS board XSTR BOARD 0 load _addr XSTR CONFIG SYS LOAD ADDR 0 Remember that the default environment is read only as it is part of the U Boot image itself Vendors normally keep some essential system variables as part of this environment There are some good reasons to keep a default environment as part of the image E Because it is read only you always have a default state to revert to E During early bootup a user supplied environment defined 72 OCTOBER 2014 WWW LINUXJOURNAL COM next may be inaccessible or m
112. ot a fixed connector Figure 2 This Code Chiet s Space page provides a very thorough step by step guide http codechief wordpress com 2013 11 11 beaglebone black serial debug connection Serial Login into the System You probably are familiar with the text consoles with Login that you make appear with Ctrl Alt F 1 6 We wanted the same but through our serial debug So we configured a tty on the BBB allowing us to connect to it via the serial line when it is booted Just add this line if it s not already present to the end of etc inittab T0 23 respawn sbin getty L tty00 115200 vt102 And make sure the kernel knows the correct console on which to output its messages In the boot Uboot uEnv txt file it should read console tty00 115200n8 console tty Figure 2 An Essential Accessory PL2303HX USB to RS232 TTL Converter Finally to connect us to the BBB through our serial debug line from another PC with a USBRS232 adapter screen dev ttyUSBO 115200 Access the Input Output Ports The Serial Ports As you previously saw the serial port must be accessed with a TTL RS232 adapter In our project we re used some old Maxim MAX3232s to do it and it works of course WWW LINUXJOURNAL COM OCTOBER 2014 89 Figure 3 The Board bbbO2 in situ with three serial ports and the serial debug port a temperature sensor on AINO a water detector on GPIO_48 a PPS input on GPIO_49 and a POWER_RE
113. p a Dynamic DNS entry in case your IP changes Mm The Tfirewalled network has to allow outgoing SSH connections Most do but if you can t SSH out from inside the firewall you might have to do something creative like run SSH on port 443 on your server That port is usually open for HTTPS traffic and since it s encrypted it s tougher to sniff out your naughty deeds COLUMNS Mm You need key pairs set up for password less logins from the computer inside the firewall to your server with the public IP Here s a demo did back in 2009 on how to set up SSH key pairs https www youtube com watch v R65HTJeObkl Once you have the prerequisites in place the process is a simple one liner First the command then the explanation ssh N R 0 0 0 0 2222 127 0 0 1 22 user remotehost The N flag tells SSH that you don t want an interactive shell you just want to establish the connection That means in order to take the tunnel down you simply press Ctrl C It can become confusing if you have an open terminal connected interactively to a remote server The tunneling still will work but If you inadvertently type exit it logs you out and kills the tunnel The R 0 0 0 0 2222 127 0 0 1 22 portion of the command is where the magic happens What you re doing Is creating a reverse tunnel which allows anyone who can access your public IP server to ssh in to the server behind the firewall In English the command
114. r computer graphics are rendered in Blender http www blender org Our audio is processed using Audacity http audacity sourceforge net and Ardour https ardour org and our stopmotion animations are created using Entangle http entangle photo org and compiled with avconv https libav org avconv html DS Why puppets Side thing my daughter Colette is a college professor who teaches puppet theater http www umbc edu theatre searls html JN We learned about the world by watching Sesame Street The Muppets and Mr Rogers Neighborhood We wanted to create a show in the same vein with a contemporary sensibility We loved the idea of merging analog craft with digital technology In addition to puppets a lot of our new content features stopmotion and hand drawn animation as well as 3 D computer Advertiser generated animation Fala Ep4 DS Why Python We can guess Thank you as always for supporting our but we d rather ask anyway advertisers by buying their products JN Python is an excellent choice for a beginner because it issues immediate TO ADVERTISER results it s very easy to read and it Can be used tor d wide variety of All Things Open http allthingsopen org applications Best of all it is included with most Linux distributions Drupalize me http www drupalize me EmperorLinux http Awww emperorlinux com DS Do you teach locally as well as on line for example in local school
115. r for you Whether you want tech tips programming ideas or just my silly insight on the best new apps for your phone the October issue of Linux Journal aims to please m Shawn Powers is the Associate Editor for Linux Journal He s also the Gadget Guy for LinuxJournal com and he has an interesting collection of vintage Garfield coffee mugs Don t let his silly hairdo fool you he s a pretty ordinary guy and can be reached via e mail at shawn linuxjournal com Or swing by the linuxjournal IRC channel on Freenode net WWW LINUXJOURNAL COM OCTOBER 2014 9 CURRENT_ISSUE TAR GZ letters AN IN DEPTH LOOK AT j HOW TOs Synchronize Your Life with ownCloud b r 12 Factor Scalable Maintainable WEB APPS A DESKTOP ENVIRONMENT A HERO A COMPUTER SYSTEM FOR THE RASPBERRY PI FOR SERVERS FOR ALGEBRA Two Column Format love being able to read Linux Journal on my laptop but can t stand the two column format that is used in the PDF version need to magnify the text due to poor eyesight and the two column format forces me to scroll down and then up constantly in order to read all the text on a page A one column format for the PDF would make for much smoother reading and navigation Please don t suggest read the EPUB version EPUB Is a terrible format Scott Randby It s tough to come up with a perfect format The PDF version is designed to look like the traditional magazine 10 OCTOBER
116. rations of an OpenStack based private cloud architecture all for less than 10K UP diff u Kernel configuration has become more and more complex through the years with the proliferation of new drivers new hardware and specific behaviors that might be needed for particular uses It has reached about 3 000 config options and that number will only increase Jean Delvare recently pointed out that a lot of those config options were relevant only to particular hardware and yet the contig system presented them to users who didn t have that hardware This seemed like a bug to him and he suggested that maintainers begin requiring proper hardware dependencies for all contig options He acknowledged this would be a big task especially for existing drivers But creating the requirement for new drivers would at least get the ball rolling and older drivers could follow along more gradually Josh Boyer agreed with all this From his work on the Fedora project he had to deal with the config system intensively and he found it difficult He said l ve gotten to the point where can somewhat guess based on the 16 OCTOBER 2014 WWW LINUXJOURNAL COM WHAT S NEW IN KERNEL DEVELOPMENT driver name which arch it s for lately the majority are for ARM but that isn t really a great way to handle things There was some resistance to the idea Greg Kroah Hartman in particular suggested that there were existing
117. resistor on the Echo wire and bridged a 1K Ohm resistor between the Echo and Ground wires This prevents blasting 5V to a pin that is rated only for 3 3V With these resistors voltage Is actually a touch higher at 3 4V which is within a tolerable level All soldered connections are covered with heat shrinking tube to avoid electrical shorts Calculating resistor types required is beyond the scope of this article but there are many handy Web based voltage divider calculators available to determine your requirements In this example a 1K and 2K Ohm resistor would reduce the current to 3 333V Wiring The Raspberry Pi is connected to the sensor with a five foot length of Figure 2 Floppy Connector CAT5 cable Because there are four connections only four of the eight twisted wires are used On each end of the selected wires soldered connectors that were compatible with the sensor pins and the pins on the Pi An old 3 5 floppy drive power connector works great for the sensor connection Figure 2 used a couple two pin PC case tan connectors salvaged from an old PC for the connections on the Pi s pins These connectors are available on line but anything you can salvage from an old PC works great Mounting The HC SRO4 is attached to a plastic case and screwed onto a piece of wood strapping The wood strapping is inserted into the sump pit facing downward and is easily adjustable and removable if needed The
118. ronment variables whereas the right hand bootdelay 10 load_addr 40000000 baudrate 1 15200 side shows that the variables have been flattened and written ina serialized form How Is the Environment Stored U Boot has two types of persistent environments 1 Default Environment Compiled In Read Only Every U Boot binary has a default built in environment of its own Figure 2a During compilation a character array called default _environment is embedded into the U Boot image This character array stores the environment variables as a list of null terminated strings with a double null terminator The contents of this array are populated conditionally based on the config options selected for your board Environment variables that are commonly used can be enabled by defining the corresponding Linearized Form of Environment Variables Figure 1 Linearized Representation of Environment Variables 70 OCTOBER 2014 WWW LINUXJOURNAL COM Valid user Environment data Default Environment Embedded in U Boot Binary CONFIG_ENV_SIZE Invalid or Unused space reserved for Env data a b Figure 2 a Type 1 Persistent Environment Read Only Embedded b Type 2 Persistent Environment User Supplied Read Write Enabled CONFIGs in your board s config Tile include contigs lt YOUR_BOARD gt h Figure 3 lists some commonly used options which once defined would make their way into the default envir
119. s If so how and where Silicon Mechanics http Awww siliconmechanics com JN We ran workshops with hacker Makerspaces in the past but found that our two man team didn t have the time and resources necessary to teach and continue producing new The Linux Journal brand s following has content for our site grown to a monthly readership nearly one million strong Encompassing the magazine Web site newsletters and DS Do you have commercial or other ambitions besides what you re doing now Such as seeing these adopted in schools much more Linux Journal offers the ideal content environment to help you reach your marketing objectives For more information please visit http www linuxjournal com advertising JN We would love to see our curriculum adopted in schools though our ambitions are more autodidactic Our primary goal is to empower young people to make their own media WWW LINUXJOURNAL COM OCTOBER 2014 113 E DS Do you have a business with this as well JN Yes We re bundling our videos and selling them as a digital download Our first complete segment Daisy s Web Dev Diary is available for purchase via Gumroad https gumroad com l daisy We re also planning to release e books for each of the four tracks of The Hello World Program And we re slowly building a merchandise store for fans to purchase Hello World themed T shirts stickers and posters http www zazzle com doto
120. s a restart command If the script returns 1 the process is fine and the script exits cleanly If the number is greater than 1 this indicates more than one raspisump py process In this instance akillall 09 raspisump py directive is initiated and the process is restarted Other Issues with Raspi Sump The HC SRO4 sensor has a fairly wide sonar field The user manual states that it works best with a 30 angle My sump pit is a busy place It has a backup pump that sits higher than the main pump on a 2x6 stud Each pump has a float ball that bounces around in the pit This results in false readings when the sensor picks up an object that enters its field This problem can be mitigated by strategically placing the sensor further away from these objects If that is not possible you can vertically insert a 3 or greater piece 66 OCTOBER 2014 WWW LINUXJOURNAL COM of PVC pipe in the sump pit and force the sensor to take its reading down the empty pipe This will focus the pulse and hide the objects in the pit that are causing problems Conclusion Raspi Sump is still in the early stages of development There are other features would like to add such as E A manual power button to start and shut down the Raspberry Pi gracetully without logging in E A small LCD display to show the current water level without opening the lid m A Web based reporting system using a Python Web framework E A Web based management i
121. spi sump raspisump py amp 64 OCTOBER 2014 WWW LINUXJOURNAL COM The ampersand amp starts the script as a background process Access to GPIO pins requires elevated privileges on the Pi To start the script manually issue the command sudo home pi raspisump raspisump py amp Figure 6 shows using the tail command to demonstrate the CSV tile being updated in real time by raspisump py What is displayed in Figure 6 Is rather strange The water depth Is bouncing around You would expect the water to be consistently higher with each reading The reason for Sump Pit Water Level 2014 07 03 22 05 35 30 j i 5 ii E C 20 a 15 10 g m oe we gt i pa 3 y5 xi ao fh Time of Day Figure 7 Graphs Generated by todaychart py this is that there is a one centimeter variance in each reading Linux is a multitasking OS and not a real time one It is not optimal for real time applications like communicating with sensors and returning precise results The best reason can come up with is that the OS is busy doing other tasks and allows raspisump py to record the reading when it is finished dealing with those other processes This brings me back to the reason use the median reading of a sorted Sample Every once in a while the script gives an invalid reading that can be way off This can trigger a false warning SMS alert even if the water is below my critical level However these readings are rare By using
122. ssions with clear and interesting examples HTML5 is not quite a language but it certainly represents a combination of APIs and tools most specifically HTML JavaScript and CSS that are the standard way to create modern Web applications It s quite amazing to see the breadth and depth of HTML5 as well as the applications that people are creating with it If you re reading this column you re probably not the right audience tor Head First HTML5 Programming which aims to teach the basics of HTML JavaScript and CSS to people who have little or no familiarity with those technologies But if you Know of someone who wants to understand how these things work its worth recommending it Another non language Is Git which has become one of my favorite and most indispensable tools It s hard to believe that used to be content with CVS and SVN given the advantages that Git brings to the table must admit that many years ago a friend of mine said that eventually would switch to a distributed version control COLUMNS system which would make life so much easier He was right although he was recommending a system that preceded Git known as Arch which don t believe Is used any longer frequently teach courses in the use of Git and I ve found that the problem for most users is not the commands but rather the understanding of what Git does and doesn t do and how the various objects work together In particul
123. stem but to be awakened only when the event occurs That s what the poll system call does See bbb_gpio py 96 OCTOBER 2014 WWW LINUXJOURNAL COM line 58 there is a link to my GitHub page with all the code for this article in the Resources section A Special Case the PPS Signal A GPS often delivers a PPS Pulse Per Second signal in order to synchronize with good accuracy the timing NMEA sentences like GPZDA The PPS signal is a TTL we can connect to a GPIO we chose GPIO_49 P9_23 Once wired we check whether the signal is present and can be read echo 49 gt sys class gpio export echo in gt sys class gpio gpi049 direction echo rising sys class gpio gpi049 edge cat sys class gpio gpi049 value 1 Be careful as to the output voltage of the PPS as the GPIOs of the BBB accept a TTL of 3 3V max The PPS signal is also a special input understood by the Linux kernel In order to enable our GPIO input as a PPS we have to compile a dts Device Tree Source file into a dtbo Device Tree Binary Object Tile with the dtc Device Tree Compiler tool see the GPS PPS P9_23 00A0 dts Tile on my GitHub page dtc O datb 0 GPS PPS P9 23 00A0 dtbo b 0 1 GP5 PP3 P9_23 00A0 dts Fetching a Good dtc This one is tricky One year ago successfully downloaded and patched dtc but now the patch is not synchronized with the versions of dtc can find Thanks to Robert Nelson execute his vers
124. tarts you get an initial module called Amateur 22 OCTOBER 2014 WWW LINUXJOURNAL COM x GPREDICT Amateur File Edit Help 2014 08 06 01 41 43 Next AO 27 m AO 27 sample N _ in 01 56 Elevation Range Rate Next Event SSP Loc Sig Loss Mean Anom Azimuth Slant Range Footprint Altitude Velocity Doppler 100M Sig Delay t UPFRONT p Detac h module Full screen Sky at a glance Time Controller Radio Control Antenna Control Configure Clone Delete Close 15 44 gt 26 4072 km 5 611 km sec AOS 2014 08 06 01 43 40 NR71PH 6092 km 804 km 7 460 km sec 2205 Hz 144 60 dB 13 58 msec 7 215 72 Orbit Phase 303 36 i t i i Uff Figure 2 Some views have drop down lists of options command When it opens you should see the main window with a sample layout given by the module named Amateur Figure 1 In the rest of this article take a look at all the various possible layouts and show just how much information is available to you The core concept in Gpredict is that of the module You can think of modules as documents in a word processor They are containers you can use to hold a number of other layout objects that display satellite information in a number of different ways When you first start Goredict you get the default Amateur module which contains a map view a polar view and a sing
125. the sump hole in his basement to avoid flooding Sump pumps are amazing devices until they re not Al shares not only his method but also his scripts tor controlling a sensor that warns him if the water level rises too much It s the perfect example of solving difficult problems with Linux Sachin Verma goes even deeper pun intended and shows how to deal with the bootloader on embedded Linux systems U Boot is commonly used in such environments and along with booting the kernel you can pass environment variables as well Sachin walks through the boot process and teaches how to customize the information passed on at boot Finally Samuel Bucquet gives a crash course in accessing the BeagleBone Black s I O ports via Python Although the Raspberry Pi and BeagleBone Black are both excellent platforms for embedded projects the BBB s sheer number of I O options make it incredible for projects with a large number of sensor needs With Samuel s help you can access those ports with the friendly and familiar Python language The Embedded issue of Linux Journal always makes me want to build something Now that BirdCam is off line the battery in my old Android phone blew up it was ugly maybe it s time to start over from scratch I m sure there are some great weatherproot IP cameras out there could use to get better shots of the winter birds Either way this is a great issue and we had a great time putting togethe
126. tion nounlist nounlist txt dream tmp dreamer input nouns trap bin rm f dream 0 no tempfile left behind echo Welcome to Dreamer To start please describe in a few sentences the dream echo you d like to explore End with DONE in all caps on its own line 40 OCTOBER 2014 WWW LINUXJOURNAL COM until input DONE o input done do echo input gt gt dream let s read another line from the user read input done echo echo Okay To confirm your dream was about cat dream for word in sed s punct g dream tr A Z a z tr n do is the word a noun Let s look if z grep E word nounlist then nouns nouns word fi done echo Hmm okay I have identified the following words as nouns echo nouns echo Are you ready to do some free association Let s begin for word in nouns do echo What comes to mind when I say word done exit 0 COLUMNS WORK THE SHELL As is immediately obvious the free association section at the end and the subsequent reassembly of the prose with the new free association words or phrases is still to come It s really broken into simple functional blocks first prompting users to share their dream then breaking down the prose into individual words and comparing them to the noun list and finally albeit not yet in its final form prompti
127. tot 114 OCTOBER 2014 WWW LINUXJOURNAL COM DS You identify on Twitter as a Creative media company and think tank https twitter com dotototdotcom Tell us more about both especially the think tank part JN The Hello World Program is Our first project As a creative media company we are producing an educational and entertaining series of videos and tutorials combining art and technology As a think tank we recognize that understanding the basics of computer science will be a necessary skill set for the future Through STEM initiatives technological literacy will be taught to students at a younger age and eventually incorporated in standard curriculum We re predicting that Linux and Python will be at the forefront of this movement We support an open source future and consider Our current project a contribution to furthering the cause Otherwise we re perpetually brainstorming new endeavors beyond puppets and video But we re not ready to talk about them yet DS Can you give us some success stories with kids JN Our booth at Maker Faire Bay Area 2013 was wildly successful It was titled Robot Puppet Party and we invited young makers to use our puppets to create their own short videos We were awarded two Editor s Choice blue ribbons But more important the kids loved it We re also launching an Indiegogo campaign called Hands On Computer Science The Hello World Program
128. uation during development is the presence of different network configurations On your home setup you may be working on a Static IP configuration using NFS But when you are out for a demo at a client location you only have DHCP available with images kept on a TFTP server U Boot is highly contigurable for such scenarios because it provides so many options You can change the network configuration modity the IP addresses of image servers and gateway servers with the help of environment variables You could assign a console over serial port or you could use netconsole or usbtty if you preter WWW LINUXJOURNAL COM OCTOBER 2014 69 FEATURE U Boot Environment Variables So What Is This U Boot Environment A simple answer to that question would be a collection of name value pairs Here name refers to the name of the environment variable to which you want to assign some value This value could be of any type string hexadecimal boolean and so forth Whatever type the value Is it is converted into a string before being stored in a linearized environment data block Each environment variable pair name value would be stored as a null terminated string So the collection of many environment variables is nothing but a null separated list with a double null terminator Figure 1 illustrates how a list of strings is actually stored The left hand side is just a logical representation of envi
129. ub com alexanderhiam PyBBIO Of course there is also the Python Adafruit Library initially for the Raspberry Pi now for the BBB https github com adafruit adafruit beaglebone io python WWW LINUXJOURNAL COM OCTOBER 2014 107 KNOWLEDGE HUB WEBCASTS Learn the 5 Critical Success Factors to Accelerate T Service Delivery in a Cloud Enabled Data Center Today s organizations face an unparalleled rate of change Cloud enabled data centers are increasingly seen as a way to accelerate IT service delivery and increase utilization of resources while reducing operating expenses Building a cloud starts with virtualizing your IT environment but an end to end cloud orchestration solution is key to optimizing the cloud to drive real productivity gains gt http Inxjr nl IBM5factors Modernizing SAP Environments with Minimum Risk a Path to Big Data Sponsor SAP Topic Big Data Is the data explosion in today s world a liability or a competitive advantage for your business Exploiting massive amounts of data to make sound business decisions is a business imperative for success and a high priority for many firms With rapid advances in x86 processing power and storage enterprise application and database workloads are increasingly being moved trom UNIX to Linux as part of IT modernization efforts Modernizing application environments has numerous TCO and ROI benefits but the transformation needs to be managed carefully a
130. use on computers within an organization The modular nature of the Red Hat SOE lets you select the most appropriate solutions to address your business IT needs SOE leads to e Dramatically reduced deployment time e Software deployed and configured in a standardized manner e Simplified maintenance due to standardization e Increased stability and reduced support and management costs e There are many benefits to having an SOE within larger environments such as e Less total cost of ownership TCO for the IT environment e More effective support e Faster deployment times e Standardization V http Inxjr nI RH SOE WWW LINUXJOURNAL COM OCTOBER 2014 109 EOF Learn GNU Linux the Fun Way d DOC SEARLS A great hello world from rural Utah ometimes a gift just falls in your lap This month it came in the form of an e mail out of the blue from Jared Nielsen one of two brothers the other is J R Nielsen who created The Hello World Program an educational web series making computer science fun and accessible to all http Awww thehelloworldprogram com If it had been just that might not have been interested But when looked at it saw it was hugely about Linux And the human story was interesting too Wrote Jared Working in rural Utah with minimal resources we combine technology and craft to make educational yet entertaining videos and tutorials Learn to c
131. ust not be used due to security concerns m A user supplied environment may be inaccessible due to a storage device malfunction or environment data corruption You shouldn t keep too much data in this default environment as it directly adds to the weight of the binary Keep only critical system variables in this environment 2 User Supplied Environment Flashed in External Storage Writable Typically vendors flash an environment data image to external storage present on your board The format of this pre built environment is again the same that is a linearized list of strings but there is a 4 byte CRC header prefixed to it This CRC is computed over the environment data Figure 2b illustrates such an environment blob with CRC data followed by valid environment data and an invalid one after that The total size of this environment data is fixed to CONFIG _ENV_SIZE during compilation So if your environment usage exceeds this size you would need to recompile your U Boot binary after increasing CONFIG _ENV_ SIZE If you do not increase the size U Boot will refuse to save the environment variables You may decide to keep this environment in external storage but you must configure the board s contig accordingly U Boot must know which storage method and at what offset will be used to hold the user environment U Boot provides a number of options to configure the location of the environment data U Boot has the
132. value of OxOFFF 4095 at the address 0x60 on i2c 1 i2cset f y 1 0x60 OxOF OXFF Write to the MCP4725 from Python The Python module to access the MCP4725 see the i2c_mcp4725 py tile on my GitHub page is a bit more complex because we try to handle all the functionalities of the DAC It depends on the python smbus package Here is how we use it import time from smbus import SMBus from i2c_mcp4725 import MCP4725 dac MCP4725 SMBus 1 int Ox60 16 safe value 2047 write to the DAC and store the value in EEPROM dac write dac_ and eeprom safevalue True read the value ouput by the dac and the content of its EEPROM dac read and eeprom print dac send a mid ramp 1 69V to 3 38V for value in range 2048 4096 write to the DAC without storing value dac write dac fast value time sleep 0 2 Python subtleties allow us simply to do this send a new value to output a voltage dac new_value check the value currently ouput by the DAC current value dac How to Read and Verify the Output Voltage The BBB has seven analog input ports named AIN O 6 They are 12 bit analog digital converters and they accept a max voltage of 1 8V To read the voltage from an analog input wire the GND P9_1 and the of the voltage you want to measure We re inject the output of our MCP4725 in AINO In this case the VDD for the MCP4725 is 3 38V the 3 3V of the PIN 3 and 4 of P9 We divide it
133. wall See Figure 2 for a complete picture The D flag tells sshuttle to run as a demon in the background The r flag tells it what remote 50 OCTOBER 2014 WWW LINUXJOURNAL COM server to connect through in this case user remotehost on port 2222 Then the last part describes the internal network behind the firewall This is something you ll need to know or figure out from your internal workstation It will ask you for your sudo password and then establish a network route through the SSH tunnel Basically you ve now not only accessed the workstation inside the firewall but you have full access to anything that workstation has access to as well Trom anywhere on the Internet COLUMNS We re All Doomed If you are feeling a bit like the nerdy hero in a modern espionage film well yeah get it There are some legitimate reasons to create tunnels like this although admittedly an actual VPN is usually the proper way to go about it It s important for those of us in charge of networks to realize how easy it is to gain access to internal systems however It s possible to block access like this at the firewall level but honestly there s always ways around the firewall if you re able to initiate internally Plus using draconian blocking methods will just inconvenience your users to the point of making them revolt So what s a network admin to do Obviously learning about network security is crucial
134. x com where Linux amp laptops converge 1 888 651 6686 i Model specifications and availability may vary t UPFRONT What s Happening above Your Head In the past I ve covered various astronomy packages that help you explore the universe of deep Space But space starts a lot closer to home It actually begins a few hundred miles above your head There are lots of things in orbit right above you In this article look at one of the tools available to help you track the satellites that are whizzing around the Earth Gpredict http gpredict oz9aec net index php A package should be available in most Linux distributions In Debian based ones you can install Gpredict with sudo apt get install gpredict This is usually a version or two behind the latest so if you want to have the newest options you always can download and build trom source Once you have it installed you can start it with the gpredict x GPREDICT Amateur File Edit Help 2014 08 06 00 54 04 _ sample N Next AQ 27 4 in 4936 m AO 27 Azimuth 196 70 Elevation 76 20 Slant Range Range Rate Next Event SSP Loc Sig Loss Mean Anom Sig Delay 94 59 Orbit Phase 1 Orbit Num 13191 km 1 606 km sec AOS 2014 08 06 01 43 40 CB5100 Footprint Altitude Velocity Doppler 100M 154 81 dB 6164 km 825 km 7 438 km sec 536 Hz 44 00 msec Figure 1 When Gpredict first s
135. you can find a similar table for each kind of I O port of the BBB on this Cape Expansion Headers page http elinux org Beagleboard Cape_Expansion_Headers Operate the GPIO The gpio_systs txt file provided with your kernel documentation explains how to work with GPIOs with a Linux kernel https www kernel org doc Documentation gpio sysfs txt These steps are for Linux kernel version 3 8 13 Each GPIO must be 65 possible digital I Os P9 O vDDO_3Vv3 9B vop_svs ESE ie sys 5V BRB sys sv ame Ree GPIO 30 11 12 GPIO 60 is Ta GPIO 48 15 16 GPIO 51 7 46 i2c2_ScCL ER i2c2_spa 21 22 GPIO_49 23 24 GPIO_15 25 26 GPIO_125 27 026 GPIO _ 123 29 30 31 E vpp_ApDc GPIO_120 33 34 aine 35q S65 ans 37 38 aino 3990400 Ani Ai 42 DGND 43 H7 DGND DGND AIE DGND P8 DSND f 2 DGND GPIO_38 4 GPIO_39 5 6 GPIO 66 7 8 GPIO 67 9 10 GPIO 45 11 12 GPIO 44 Gpio 23 13 14 GPIO 47 15 16 GPIO_46 17 18 GPIO 22 19 20 GPIO 63 21 22 GPIOS7 GPIO_36 23 24 GPIO_33 GPIO_32 25 26 GPIO6t GPIO 86 27 28 GPIO 88 GPIO_87 29 30 GPIO89 GPIO 10 31 Sel GPIO 11 _ GPoS 33 s4 GRIOS GPIO 8 35 36 GPIO_80 GPIo_78 37 38 GPIO 79 GPIO 76 39 40 GPIO_77 GPIO_74 41 42 GPIO7S GPIO 72 43 44 GPIO 73 GPIO_70 45 46 GPIO71 Figure 7 Mapping GPIO Kernel Numbers with P8 and P9 Pinouts enabled independently so for the GPIO_48 on P9_15 echo 48 gt sys class gpio export Next

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