Xen installation and configuration
Contents
1. THIS GUIDE IS DESIGNED TO GET A Xen server up and running in no time It is a simple copy and paste guide which should get you through a bare bones install with minimal trouble and time Xen is an exciting and still relatively new tech Xen in stall ati on nology more information can be obtained and configuration by visiting the Xen homepage at http www xensource com and also by LEIGH GRIFFIN AND JOHN RONAN Leigh is a student assistant researcher at the TSSG reading The In evitability of Xen by Waterford Institute of Technology He has now PA returned to WIT to complete his studies in the B Sc Crowcroft et al 1 The only limitations you MAREE computing Degree will find with Xen will derive from your grin etssg Br9 hardware or your ingenuity John Ronan is a senior researcher at the TSSG As this guide is aimed at beginners it is going to Waterford Institute of Technology and also a radio theinstallati eon the bi ham EI7IG When not experimenting with new net COVER Ue insta a LOM OL SCE ATO ME ENS DEAR work technologies he can be found bouncing AX25 packages The binary packages are recommended packets through LEO satellites for people who are new to Xen and are uncom jronan tssg org fortable with the range of configuration options that the source install offers The latest stable release of Xen can be found at http www xensource com products downloads The sources are also available from BitTorren2. etc xen so that is the place where we will leave the configuration files because the Xen software automatically scans this directory for the match ing file We use etc xen myfirstdomain sxp as the name for our first domain Here is a copy of the domain that we created name myfirstdomain kernel boot vmlinuz 2 6 12 6 xenU root dev hda1 memory 64 disk I file virtual images vm01 img hda1 w file virtual images vm01 swap img hda2 w network vif dhcp off ip 10 0 0 50 netmask 255 0 0 0 gateway 10 0 0 254 hostname myfirstdomain yourdomain org extra 3 The ip addresses should match ranges within your organization s network It is simply a case of sorting the networking out more then anything else We set DHCP to be off in our instance but if your network requires DHCP to be on as a means of dealing with addresses it s simply a matter of chang ing off to on The root value is the value that we set earlier in the etc fstab file The mappings between the swap and root values that we set earlier in the etc fstab file are also evident in the specification of the disk value Note that the memory value is the amount of RAM in megabytes that you are going to give to this domain In this case our domain is going to receive 64 MB of RAM to work with Now to start the machine you need to be logged in as root Once in as root you have access to the Xen software If yo
3. RAM while still keeping the DIMMs balanced and reboot the machine Currently the binary install can only cope with a max imum of 3583 MB of RAM To use more RAM a source install needs to be performed and PAE support must be built into the kernel however this topic lies outside the scope of this guide Creation of Domains Now that we have the Xen software installed it is time to get to the cre ation of the virtual machines First we are going to create a storage area for our virtual machines xen mkdir virtual amp amp cd virtual Here we are going to create two directories in which to store and configure the images xen virtual mkdir vm_base xen virtual mkdir images We will create a default image and swap image from which our virtual machines will be derived Execute the following commands LOGIN FEBRUARY 2007 xen virtual dd if dev zero of virtual images vm_base img bs 1024k count xxxx xen virtual dd if dev zero of virtual images vm_base swap img bs 1024k count xxx Note that the value that count specifies is the size the image will be in megabytes Simply change it to a value that will suit your needs only your machine capacity is the limit See p 65 for sample file sizes Now we need to format the base image to be ext3 so that it can serve as our journaling filesystem We have chosen ext3 as it is faster than ext2 and has stronger guarantees for data integrity 4 xen virtual mkfs e
4. Xen server other xen domains floated and other hosts on the same network as yours It should also be possible to ssh into the domain When you are finished with your domain and wish to exit it you can doa shutdown as normal which will send you back to the original Xen domain from where you came or if you wish to leave it running and wish to return to Xen simply hold down CTRL This will take you back to Xen If you run xm list you should see your domains that are successfully floated in cluding information such as how much memory they are allocated and their domain name To get a console to one of them simply run xm console myfirstdomain where myfirstdomain is the name of the domain we specified within the configuration file and is the name that appears in the list of domains we see when xm list is run If you wish to create more domains it is simply a matter of copying the base image xen cp pf virtual images vm_base img virtual images vm0X img xen cp pf virtual images vm_base swap img virtual images vm0X swap img The vmOX just needs to be changed to a new unique number or name A corresponding config file needs to be created in etc xen which refer ences the newly created image file in its disk parameter If you wish to have your domains started automatically at startup a link must be created in the auto folder that Xen scans as the system boots This can be achieved by doing this xen In s etc xen myfir
5. created which is enough for 32 machines to be created If you need more change the 63 to a number you desire When this is done restart the machine and everything should be working fine RESOURCES AND LINKS 1 J Crowcroft et al The Inevitability of Xen login 30 no 4 2005 10 13 Available at http www usenix org publications login 2005 08 pdfs crowcroft pdf 2 Xen Users Manual Available at http www cl cam ac uk Research SRG netos xen readmes user 3 Filesystem Hierarchy Standard Group R Russell et al eds File System Hierarchy Standard 2004 Available at http www pathname com fhs pub fhs 2 3 pdf 4 M K Johnson Red Hat s New Journaling File System ext3 2001 Available at http www redhat com support wpapers redhat ext3 advantages 5 E Timme The Perfect Xen 3 0 Setup for Debian 2006 Available at http www howtoforge com perfect_setup_xen3_debian Acknowledgment This work is partially supported by the IST ENABLE project under the European Commission s 6th framework program XEN INSTALLATION AND CONFIGURATION 43
6. ext3 defaults 12 dev hda2 none swap sw 00 dev pts devpts gid 5 mode 620 00 none dev shm tmpfs defaults 00 These values will map to the configuration file values for the root and swap later on in the configuration of the virtual domains themselves Our last configuration option sees the creation of the hosts file 127 0 0 1 localhost localdomain localhost The following lines are desirable for IPv6 capable hosts 1 Ip6 localhost ip6 loopback fe00 0 ip6 localnet ff00 0 ip6 mcastprefix ff02 1 ip6 allnodes ff02 2 ip6 allrouters ff02 3 ip6 allhosts Now we leave the chroot environment with exit All that is left is for us to copy the kernel modules to our virtual machine and unmount the image xen virtual vm_base cp dpR lib modules 2 6 12 6 xenU virtual vm_base lib modules xen virtual vm_base mv virtual vm_base lib tls virtual vm_base lib tls disabled xen virtual vm_base umount virtual vm_base The base image is now complete Creation of Virtual Domains Now that we have a base image to work off of it is time to go and make some virtual machines We will do this by copying the base image like so xen virtual vm_base cp pf virtual images vm_base img virtual images vm01 img 40 LOGIN VOL 32 NO 1 LOGIN FEBRUARY 2007 xen virtual vm_base cp pf virtual images vm_base swap img virtual images vm01 swap img Now we create a configuration file for this new domain Xen is located in
7. re the base system using base config A menu with various installation options will be presented to you The important things to con figure are 1 Users and passwords This is where you set the default user name password and root password This is an important part as each im age subsequently created from the base image will have these default passwords which will need to be changed 2 The time zone XEN INSTALLATION AND CONFIGURATION 39 3 Which software to install When the program prompts for additional software to be installed we choose none as this is the base image from which the other virtual machines will later be derived Each de rived machine can be customized when it is ready When you are satisfied with the system simply hit return and you are fin ished configuring the base system There are some small configurations still to be completed First remove the hostname from the system We remove the hostname because deboot strap copies this from the host machine to the newly created image so both will have the same hostname xen rm f etc hostname Now we need to create our networking interfaces by editing etc network interfaces auto lo iface lo inet loopback address 127 0 0 1 netmask 255 0 0 0 Next we edit the fstab file it must end up looking exactly like the follow ing in order to represent the internal structure of the virtual image its mountpoints and its filesystem types dev hda1
8. services at boot time the following commands need to be run xen update rc d xend defaults 20 21 xen update rc d xendomains defaults 21 20 The final additions to be made are to add the Xen kernel to the bootloader program Grub Scroll through the file until you find the line that reads BEGIN AUTOMAGIC KERNELS LIST Just above that is the place where we must make our addition to the file Enter the following text title Xen 3 0 XenLinux 2 6 12 kernel boot xen gz dom0_mem 64000 module boot vmlinuz 2 6 12 xen0 root dev hda1 ro console ttyO Note that it is important to make sure that your root is indeed dev hdal If it is not simply change the value after root to match it If you are unsure what your root name is scroll further down the menu lst file and you will see the default kernel and its root value Reboot the machine at the boot prompt Grub will now list Xen 3 0 XenLinux 2 6 12 as the first kernel and boot it automatically Everything should load normally and you will be given your standard login If the machine does not boot the following may fix the problem If the Xen machine executes a hard reboot as it is starting up the problem rests with the amount of RAM in your machine You will get no error mes sage with this problem and the last thing you will see is a line that says Scrubbing free RAM j Then the screen will go black and do a hard reboot The solution is to remove the excess
9. stdomain sxp etc xen auto Restart the machine and see if the domains come up successfully Extra Configuration The final configuration that must be done in order to create more than three domains may need to be performed now Each virtual image and its swap area run on a loop each The default num ber of loops is 7 If you attempt to float a fourth or fifth domain you will get this error Error Device 769 vbd could not be connected Backend device not found This means that we can only create at most three domains with this setup as each requires two loops to run So we need to do some editing to vital files Again ensure a backup has been made in case things go wrong We need to edit the modules configuration file etc modules conf and add these options anywhere in the file options loop max_loop 64 rmmod loop modprobe loop Once done if you are running devfs the new loops should have been auto matically created LOGIN FEBRUARY 2007 If you still only see seven values for loop you need to edit dev MAKEDEV and recompile it to make the changes take place This is a very big file you need to scroll down until you see the following loop for partin01234567 do makedev loop part b 7 part disk done This needs to be changed to loop for part in seq 0 63 do makedev loop part b 7 part disk done Then recompile by running makedev loop Verify in dev that there are now 64 loops
10. t sites among others however we recommend going with the official releases to ensure validity security and stability 2 We obtained the 3 0 1 binary install file and thus will use this as a refer ence for the rest of the guide simply replace 3 0 1 with your 3 0 x in the relevant positions in order to install the software successfully The Linux Filesystem Hierarchy Standard recommends placing the source file in the usr sre folder and that s where we will put it and unpack it 3 Prerequisites We ran the following commands to install the dependency packages and to remove some outdat ed and unnecessary packages using Debian xen apt get remove exim4 exim4 base lpr nfs common portmap pidentd pcmcia cs pppoe pppoeconf ppp pppconfig xen apt get install screen ssh debootstrap python python2 3 twisted iproute bridge utils libcurl3 dev Now that we have the necessary files installed lets extract the software from its tar file and run the install script LOGIN FEBRUARY 2007 XEN INSTALLATION AND CONFIGURATION 37 38 LOGIN VOL 32 NO 1 xen usr src cd xen 3 0 1 install xen usr src xen 3 0 1 install install sh xen usr src xen 3 0 1 install mv lib tls lib tls disabled The last command is necessary to avoid the emulation slowdown problems with the glibc libraries that are installed by default 2 You should now have the Xen software installed on your computer To start the Xen
11. u type in xm help you will get a listing of the available commands and how to use them To create a domain we will execute the following command xen xm create c myfirstdomain sxp There is no need to specify the exact path to the myfirstdomain file as the Xen software automatically looks in etc xen for a file matching the config uration file you are using If you placed the configuration file elsewhere simply insert the complete path to the file The c flag is used to ask for a console for the domain you have just launched If all goes ok you should see the machine booting up and even tually you will get to the login prompt If you get an error saying the domain failed to balloon it is an error associated with allocating too little memory to the virtual machine You have not allocated enough RAM to allow domU to boot successfully You will have to use the xm destroy myfirstdomain to stop the domain then edit the configuration file to allo cate more memory to your domain and use the create command to launch the domain XEN INSTALLATION AND CONFIGURATION 41 42 LOGIN VOL 32 NO 1 Log in with the default username and password that you specified in the configuration of the base system It is a good idea now to change the default password This is a major security issue as each domain is created from the same base system and thus has the same username and pass words With your domain you should be able to ping the master
12. xt3 virtual images vm_base img Answer yes to the question prompted regarding the warning about the block special device Now we need to configure the swap file to be a swap area xen virtual mkswap virtual images vm_base swap img Next it s time to install the Debian base system to our newly created image First though we need to mount our image xen virtual mount o loop virtual images vm_base img virtual vm_base Debootstrapping the Base Image We run the debootstrap command to download all the prerequisite pack ages using the following command xen virtual debootstrap arch i386 sarge virtual vm_base http ftp2 de debian org debian Now change root and configure the images apt program to specify how we want to pull down our software and updates xen virtual chroot virtual vm_base xen apt setup During the standard apt setup you will be asked some basic questions regarding your location and which mirror you wish to use to speed up the process When this is done edit the sources list that comes with apt and change the word testing to stable wherever it appears in the file Now update your software repository xen apt get update The next step in the installation process involves setting up the locales for your region xen apt get install localeconf Choose the locales to install depending on your country e g en_lE ISOxxxx for Ireland or en_US SOxxxx for the United States Next configu
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