Using OpenVZ
OS Templates – Linux Distribution Install Media
The vzctl command is used to create and configure OpenVZ containers. Before you can create a container, you need install media for the Linux distribution you want to install. OpenVZ can NOT use CD / DVD install media (NOR .iso disk image files). OpenVZ requires what it calls an OS Template to create a container for a given Linux distribution. You can download a number of pre-created OS Templates from the OpenVZ website. This is the recommended route for new OpenVZ users. Once you are more familiar with OpenVZ you may want to create your own OS Templates from scratch using a variety of recipes available on the OpenVZ wiki. You can find pre-created OS Templates provided by the OpenVZ Project here:
http://download.openvz.org/template/precreated/
You can also find community contributed OS Templates here:
http://download.openvz.org/contrib/template/precreated/
Download the desired OS Template file and place it in the /vz/template/cache directory on your CentOS 5 host node.
cd /vz/template/cache
wget http://download.openvz.org/template/precreated/contrib/centos-5-i386-default.tar.gz
Creating Your First Container
To create a container you use the vzctl command with the create option and a few other parameters. You will need to decide on a unique container ID number (CTID). You will also need some additional information: What OS Template do you want to install from? What IP address will it have? What hostname do you want to give it? What initial resources do you want it to have (taken from a sample configuration template)? These are all set with the following parameters:
–ostemplate {template name}
–conf {config name}
–ipadd {nn.nn.nn.nn}
–hostname {FQDN}
Here is a complete example:
vzctl create 101
–ostemplate centos-5-i386-default
–conf vps.basic
–ipadd 192.168.1.4
–hostname mynew.vps.com
That will create a directory named /vz/private/{CTID} and extract the OS Template into it. It will also copy the specified config file to /etc/vz/conf/{CTID}.conf to create a configuration for the container. Please note that the values given for --ostemplate and --conf do NOT match up to full OS Template nor the configuration filenames… and are somewhat truncated.
The vps.basic configuration is just that, very basic… with a somewhat conservative amount of resources given to the container. For a look at the various resource parameters and their values, feel free to have a look at the sample configuration files in the /etc/vz/conf directory. You can create your own configuration samples (as many as you like) using the vzsplit command (man vzsplit) or by copying existing config files to new files and editing them.
After you create a machine you need to set a few additional parameters using the vzctl set command. Here’s an example:
vzctl set 101
–name mynew
–nameserver “205.171.2.65 205.171.3.65″
–diskspace 10G:10G
–save
That will update your container’s config file (in this example /etc/vz/conf/101.conf). Any time you run the vzctl set command if you don’t include the --save parameter it will not save the configuration changes to your config file… but if the container is running it will dynamically change the parameters in the running container for that session. You will almost always want to include the --save as the last parameter for the vzctl set command.
If you want to have the vm started at boot, run
vzctl set 101 –onboot yes –save
To set a hostname and IP address for the vm, run:
vzctl set 101 –hostname test.example.com –save
vzctl set 101 –ipadd 192.168.0.101 –save
Next we set the number of sockets to 120 and assign a few nameservers to the vm:
vzctl set 101 –numothersock 120 –save
vzctl set 101 –nameserver 213.133.98.98 –nameserver 213.133.99.99 –nameserver 213.133.100.100 –nameserver 145.253.2.75 –save
(Instead of using the vzctl set commands, you can as well directly edit the vm’s configuration file which is stored in the /etc/vz/conf directory. If the ID of the vm is 101, then the configuration file is /etc/vz/conf/101.conf.)
To start the vm, run
vzctl start 101
To set a root password for the vm, execute
vzctl exec 101 passwd
You can now either connect to the vm via SSH (e.g. with PuTTY), or you enter it as follows:
vzctl enter 101
To leave the vm’s console, type
exit
To stop a vm, run
vzctl stop 101
To restart a vm, run
vzctl restart 101
To delete a vm from the hard drive (it must be stopped before you can do this), run
vzctl destroy 101
To get a list of your vms and their statuses, run
vzlist -a
[root@server1 cache]# vzlist -a
VEID NPROC STATUS IP_ADDR HOSTNAME
101 18 running 192.168.0.101 test.example.com
[root@server1 cache]#
To find out about the resources allocated to a vm, run
vzctl exec 101 cat /proc/user_beancounters
[root@server1 cache]# vzctl exec 101 cat /proc/user_beancounters
Version: 2.5
uid resource held maxheld barrier limit failcnt
101: kmemsize 1508202 1661695 11055923 11377049 0
lockedpages 0 0 256 256 0
privvmpages 5430 7102 65536 69632 0
shmpages 381 381 21504 21504 0
dummy 0 0 0 0 0
numproc 19 21 240 240 0
physpages 2489 2775 0 2147483647 0
vmguarpages 0 0 33792 2147483647 0
oomguarpages 2489 2775 26112 2147483647 0
numtcpsock 5 5 360 360 0
numflock 3 4 188 206 0
numpty 0 1 16 16 0
numsiginfo 0 2 256 256 0
tcpsndbuf 44720 0 1720320 2703360 0
tcprcvbuf 81920 0 1720320 2703360 0
othersockbuf 13144 14356 1126080 2097152 0
dgramrcvbuf 0 8380 262144 262144 0
numothersock 11 13 120 120 0
dcachesize 0 0 3409920 3624960 0
numfile 503 531 9312 9312 0
dummy 0 0 0 0 0
dummy 0 0 0 0 0
dummy 0 0 0 0 0
numiptent 10 10 128 128 0
[root@server1 cache]#
The failcnt column is very important, it should contain only zeros; if it doesn’t, this means that the vm needs more resources than are currently allocated to the vm. Open the vm’s configuration file in /etc/vz/conf and raise the appropriate resource, then restart the vm.
To find out more about the vzctl command, run
man vzctl
What if yum is missing in my container?
The pre-created OS Templates provided by the OpenVZ Project do not have yum installed (contrib OS Templates are more likely to have yum installed) and that seems to miff a lot of users. The reason is that some OpenVZ system administrators prefer to use a tool on the host node named vzyum that allows them to do yum type operations on containers from the host node. Why would you want to do that? Because the yum database and file caches can sometimes take up a significant amount of diskspace (and bandwidth) if each container has its own copy of yum. Using vzyum on the host node, there is a single yum database / cache and the software packages only have to be downloaded once.
There have been some technical issues using vzyum on CentOS 5 x86_64 host nodes (it worked flawlessly in CentOS 4) and as a result vzyum has fallen somewhat out-of-favor with CentOS 5… but the official pre-created OS Templates are still optimized for those using vzyum.
There is a wiki page on the OpenVZ wiki that explains how to install yum in a container if you want it. Basically you download all of the rpm packages needed for yum and install them with rpm.
In Closing
This article has only covered the very basics of OpenVZ. Topics not covered include container monitoring / resource management, configuration file editing / creation (see the vzsplit man page), the container filesystem, or any additional tasks necessary to become a productive OpenVZ system administrator. Also note that OpenVZ has two types of network adaptors and only the basic / default venet was covered. The veth network adaptor has a wider range of capabilities.
The documentation provided by the OpenVZ Project is really good and there is plenty of it. Be sure and read the Users Guide PDF guide for the most comprehensive documentation. The Users Guide is a little dated though as it was written before the addition of the veth network device, checkpointing and migration. Also available are the man pages for all of the various commands. When you want to get into container migration be sure and read the vzmigrate man page.
You are encouraged to get involved and participate in the OpenVZ project by visiting the OpenVZ website, using the forums, the IRC channel (#openvz on the Freenode IRC network), as well as filing bugs if you run across any at bugzilla.openvz.org. Get familiar with the OpenVZ website as there is a lot of material there.
Additional Resources
OpenVZ Project website
Interview with OpenVZ Project Manager
OS Virtualization vs. Hardware Virtualization video presentation from Linuxfest Northwest 2008
Container migration demo video
Performance evaluation of Xen vs. OpenVZ by HP Labs
OpenVZ blog
Parallels Inc.
Linux-VServer website
Interview with Linux-VServer Project Leader
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One Comment to “Using OpenVZ”
really very helping……very informative….thanks to give us this knowledge