Creating OpenVZ LiveCD based on Centos 4.4

This article is a step by step guide explaining how to add OpenVZ functionality to Centos 4.4 LiveCD. As a result, you will have a LiveCD, that can boot in various OpenVZ kernels (rhel4-2.6.9, 2.6.18, rhel5-2.6.18, 2.6.20) and in original CentOS kernel also. After booting from CD, you will be able to create VEs, start them, enter them - i.e. perform common OpenVZ activity.

CentOS 5 LiveCD is already announced and as soon as it will be available we'll update the article.

General actions

It is quite easy to add OpenVZ functionality to existent LiveCD. The most difficult work is already done by the original LiveCD creators. But it requires pretty much hand job. Probably some day some good guy will automatize this process. ;)

Actually you need to know the following general actions - everything else is only technical details:

• Get a copy of CentOS 4.4 LiveCD iso image
• Use unsquashfs tool to extract the contents of *.mo files from CD and construct booted LiveCD root filesystem from extracted files
• Create OpenVZ kernel packages with squashfs and unionfs support
• Get OpenVZ user-space tools packages: vzctl, vzquota, vzpkg, ... and some precreated templates
• Remove some packages from booted LiveCD root filesystem (conflicting with OpenVZ kernel packages and unnecessary packages to free some space)
• Install OpenVZ kernels, tools and templates in LiveCD root filesystem
• Using mksquashfs tool compress booted CD root filesystem
• Modify initrd image: add there kernel modules for OpenVZ kernels
• Introduce small modifications to isolinux configuration file
• Create new iso image

Technical details

This part contents detailed description of LiveCD creation. I've removed the output of some commands in order to simplify the reading.

Creating booted LiveCD root filesystem

Create a directory, that will be our "workbench":

# cd ~
# mkdir workbench
# cd workbench

First of all we need some raw material - CentOS 4.4 LiveCD:

# wget http://mirror.nsc.liu.se/CentOS/4.4/isos/i386/CentOS-4.4-i386-LiveCD.iso
# wget http://mirror.nsc.liu.se/CentOS/4.4/isos/i386/md5sum.livecd
# md5sum --check md5sum.livecd 
CentOS-4.4-i386-LiveCD.iso: OK

Copy the contents of CD to the directory, where we will form the OpenVZ LiveCD filesystem. I named this directory "ovz-livecd":

# mkdir ovz-livecd
# mkdir mount
# mount -o loop -t iso9660 CentOS-4.4-i386-LiveCD.iso mount/
# cp -a mount/* ovz-livecd/
# umount mount
# rm -rf mount

You can see, that ovz-livecd/base/ directory owns several *.mo files - images of squashfs filesystem, and each image holds one directory of booted LiveCD root filesystem: bin, usr and so on:

# ls -1 ovz-livecd/base
bin.mo etc.mo lib.mo root.mo sbin.mo usr.mo var.mo

In order to decompress these images we need squashfs tools. The source archive of squashfs contents patch for the kernel (to be able mount squashfs), and user-space tools for compressing/decomprassing usual filesytem into squashfs filesystem. Well, we don't need the kernel patch right now (but we will need it later), we only want to install squashfs user-space tools:

# wget wget http://switch.dl.sourceforge.net/sourceforge/squashfs/squashfs3.2-r2.tar.gz
# tar xzf squashfs3.2-r2.tar.gz
# cd squashfs3.2-r2/squashfs-tools/
# make
cc mksquashfs.o read_fs.o sort.o -lz -lpthread -lm -o mksquashfs
cc unsquashfs.o -lz -o unsquashfs
# cp mksquashfs /usr/bin/
# cp unsquashfs /usr/bin/
# cd ~/workbench

Well, having the intruments in hand, why not extract the images? Create a directory, called livecd-root, that will store the root filesystem for booted LiveCD. I.e. it will content /bin, /sbin, /etc and other directories, which you will see after booting the LiveCD. Unfortunately unsquashfs tool is not very convenient, and I found only this way to use it:

# mkdir livecd-root

# unsquashfs ovz-livecd/base/bin.mo 
# mv squashfs-root/bin/ livecd-root/
# rm -rf squashfs-root

# unsquashfs ovz-livecd/base/etc.mo 
# mv squashfs-root/etc/ livecd-root/
# rm -rf squashfs-root

# unsquashfs ovz-livecd/base/lib.mo 
# mv squashfs-root/lib/ livecd-root/
# rm -rf squashfs-root

# unsquashfs ovz-livecd/base/root.mo 
# mv squashfs-root/root/ livecd-root/
# rm -rf squashfs-root

# unsquashfs ovz-livecd/base/sbin.mo 
# mv squashfs-root/sbin/ livecd-root/
# rm -rf squashfs-root

# unsquashfs ovz-livecd/base/usr.mo    # this action takes some time, be patient ;)
# mv squashfs-root/usr/ livecd-root/
# rm -rf squashfs-root

# unsquashfs ovz-livecd/base/var.mo
# mv squashfs-root/var/ livecd-root/
# rm -rf squashfs-root

Yet we have nearly complete root filesystem of booted LiveCD in livecd-root directory. However some things are missing, and I guess you know what are they: /dev, /proc, /sys, /tmp and /boot directories. We need them, because some tools (rpm, bash, ...) will not work without them in chrooted environment later.

# mkdir root/dev
# cp -a /dev/* root/dev
# mkdir root/proc
# mount -t proc proc root/proc/
# mkdir root/sys
# mount -t sysfs sysfs root/sys/
# mkdir root/tmp
# mkdir root/boot

That's it. We have booted LiveCD root filesystem in livecd-root directory. Now we can chroot in this directory and install all needed packages. But what packages do we need?

• OpenVZ kernels
• OpenVZ tools: vzctl, vzquota, vzpkg, vzrpm43, vzrpm44, vzyum
• OpenVZ template metadatas: centos-4, fc-3, fc4 and fc-5
• Some OpenVZ precreated templates
• Some CentOS tools updates: sqlite package

Tools and templates related packages can be simply downloaded and installed. But it is not so easy with kernel. Usual OpenVZ kernel won't work: it doesn't support squashfs. The next chapter explains how to create RPM package with OpenVZ kernel, that supports squashfs

Building OpenVZ kernels and kernel modules

To be continued...

Obrezki

TODO rpms/ rpms/kernel rpms/tools rpms/update

Uninstall lsctp-tools package, because these tools they need kernel version prior to 2.6.10:

rpm -e lksctp-tools-1.0.2-6.4E.1.i386

Uninstall kernel-module-xfs package, because these modules are compiled against original

rpm -e kernel-module-xfs-2.6.9-42.livecd.c4-0.1-3.i686

cd /tmp/rpms/kernel rpm -ivh kernel-smp-2.6.18-ovz028stab033.1.i686.rpm rpm -e kernel-2.6.9-42.livecd.c4

cd /tmp/rpms/updates rpm -Uvh sqlite-3.3.6-2.i386.rpm

1. rpm -ivh vz*

Preparing... ########################################### [100%]

  1:vzrpm44                ########################################### [  8%]
  2:vzrpm44-python         ########################################### [ 15%]
  3:vzrpm43-python         ########################################### [ 23%]
  4:vzrpm43                ########################################### [ 31%]
  5:vzyum                  ########################################### [ 38%]
  6:vzquota                ########################################### [ 46%]
  7:vzctl-lib              ########################################### [ 54%]
  8:vzctl                  ########################################### [ 62%]
  9:vzpkg                  ########################################### [ 69%]
 10:vztmpl-centos-4        ########################################### [ 77%]
 11:vztmpl-fedora-core-3   ########################################### [ 85%]
 12:vztmpl-fedora-core-4   ########################################### [ 92%]
 13:vztmpl-fedora-core-5   ########################################### [100%]

External Links

• Official CentOS community website
• Linux kernel website
• RedHat Inc. website
• squashfs website
• uninonfs official homepage