Installing And Using OpenVZ On CentOS 5.2

Version 1.0
Author: Falko Timme <ft [at] falkotimme [dot] com>
Last edited 07/09/2008

In this HowTo I will describe how to prepare a CentOS 5.2 server for OpenVZ. With OpenVZ you can create multiple Virtual Private Servers (VPS) on the same hardware, similar to Xen and the Linux Vserver project. OpenVZ is the open-source branch of Virtuozzo, a commercial virtualization solution used by many providers that offer virtual servers. The OpenVZ kernel patch is licensed under the GPL license, and the user-level tools are under the QPL license.

This howto is meant as a practical guide; it does not cover the theoretical backgrounds. They are treated in a lot of other documents in the web.

This document comes without warranty of any kind! I want to say that this is not the only way of setting up such a system. There are many ways of achieving this goal but this is the way I take. I do not issue any guarantee that this will work for you!

1 Installing OpenVZ

In order to install OpenVZ, we need to add the OpenVZ repository to yum:

cd /etc/yum.repos.d
wget http://download.openvz.org/openvz.repo
rpm --import http://download.openvz.org/RPM-GPG-Key-OpenVZ

The repository contains a few different OpenVZ kernels (you can find more details about them here: http://wiki.openvz.org/Kernel_flavors). The command

yum search ovzkernel

shows you the available kernels:

[root@server1 yum.repos.d]# yum search ovzkernel
Loading "fastestmirror" plugin
Loading mirror speeds from cached hostfile
 * base: ftp.halifax.rwth-aachen.de
 * openvz-kernel-rhel5: openvz.proserve.nl
 * updates: ftp.halifax.rwth-aachen.de
 * addons: ftp.halifax.rwth-aachen.de
 * openvz-utils: openvz.proserve.nl
 * extras: ftp.halifax.rwth-aachen.de
openvz-kernel-rhel5       100% |=========================|  951 B    00:00
primary.xml.gz            100% |=========================|  22 kB    00:00
openvz-ker: ################################################## 14/14
openvz-utils              100% |=========================|  951 B    00:00
primary.xml.gz            100% |=========================| 6.7 kB    00:00
openvz-uti: ################################################## 26/26
ovzkernel-ent.i686 : The Linux kernel compiled for huge mem capable machines.
ovzkernel-PAE.i686 : The Linux kernel compiled for PAE capable machines.
ovzkernel-ent-devel.i686 : Development package for building kernel modules to match the ent kernel.
ovzkernel-PAE-devel.i686 : Development package for building kernel modules to match the PAE kernel.
ovzkernel.i686 : Virtuozzo Linux kernel (the core of the Linux operating system)
ovzkernel-xen.i686 : The Linux kernel compiled for Xen VM operations
ovzkernel-xen-devel.i686 : Development package for building kernel modules to match the kernel.
ovzkernel-devel.i686 : Development package for building kernel modules to match the kernel.
[root@server1 yum.repos.d]#

Pick one of them and install it as follows:

yum install ovzkernel

This should automatically update the GRUB bootloader as well. Anyway, we should open /boot/grub/menu.lst; the first kernel stanza should now contain the new OpenVZ kernel. The title of that kernel just reads "CentOS". I think it's a good idea to change that title and add something with "OpenVZ" to it so that you know that it's the OpenVZ kernel. Also make sure that the value of default is 0 so that the first kernel (the OpenVZ kernel) is booted automatically instead of the default CentOS kernel.

vi /boot/grub/menu.lst

# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /boot/, eg.
#          root (hd0,0)
#          kernel /vmlinuz-version ro root=/dev/VolGroup00/LogVol00
#          initrd /initrd-version.img
#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS OpenVZ (2.6.18-53.1.19.el5.028stab053.14)
        root (hd0,0)
        kernel /vmlinuz-2.6.18-53.1.19.el5.028stab053.14 ro root=/dev/VolGroup00/LogVol00
        initrd /initrd-2.6.18-53.1.19.el5.028stab053.14.img
title CentOS (2.6.18-92.1.1.el5)
        root (hd0,0)
        kernel /vmlinuz-2.6.18-92.1.1.el5 ro root=/dev/VolGroup00/LogVol00
        initrd /initrd-2.6.18-92.1.1.el5.img
title CentOS (2.6.18-92.el5)
        root (hd0,0)
        kernel /vmlinuz-2.6.18-92.el5 ro root=/dev/VolGroup00/LogVol00
        initrd /initrd-2.6.18-92.el5.img

Now we install some OpenVZ user tools:

yum install vzctl vzquota

Open /etc/sysctl.conf and make sure that you have the following settings in it:

vi /etc/sysctl.conf

[...]
net.ipv4.ip_forward = 1
net.ipv4.conf.default.proxy_arp = 0
net.ipv4.conf.all.rp_filter = 1
kernel.sysrq = 1
net.ipv4.conf.default.send_redirects = 1
net.ipv4.conf.all.send_redirects = 0
net.ipv4.icmp_echo_ignore_broadcasts=1
net.ipv4.conf.default.forwarding=1
[...]

If you need to modify /etc/sysctl.conf, run

sysctl -p

afterwards.

The following step is important if the IP addresses of your virtual machines are from a different subnet than the host system's IP address. If you don't do this, networking will not work in the virtual machines!

Open /etc/vz/vz.conf and set NEIGHBOUR_DEVS to all:

vi /etc/vz/vz.conf

[...]
NEIGHBOUR_DEVS=all
[...]

SELinux needs to be disabled if you want to use OpenVZ. Open /etc/sysconfig/selinux and set the value of SELINUX to disabled:

vi /etc/sysconfig/selinux

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#       enforcing - SELinux security policy is enforced.
#       permissive - SELinux prints warnings instead of enforcing.
#       disabled - SELinux is fully disabled.
SELINUX=disabled
# SELINUXTYPE= type of policy in use. Possible values are:
#       targeted - Only targeted network daemons are protected.
#       strict - Full SELinux protection.
SELINUXTYPE=targeted

Finally, reboot the system:

reboot

If your system reboots without problems, then everything is fine!

Run

uname -r

and your new OpenVZ kernel should show up:

[root@server1 ~]# uname -r
2.6.18-53.1.19.el5.028stab053.14
[root@server1 ~]#