Editing 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 the CD, you will be able 
to create [[VE]]s, start them, enter them - i.e. perform [[Getting started with OpenVZ live CD | 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 accomplish the following general actions - everything else is only technical details:
* Get a copy of CentOS 4.4 LiveCD image 
* Use <tt>unsquashfs</tt> tool to extract the contents of *.mo files, located on the image
* Construct '''booted''' LiveCD root filesystem from extracted files
* Create OpenVZ kernel RPM-packages  with <tt>squashfs</tt> support
* Compile <tt>unionfs</tt> kernel modules against OpenVZ kernels
* Get OpenVZ tools RPM-packages: vzctl, vzquota, vzpkg, etc. Get template metadatas and precreated templates
* Remove some RPM-packages from '''booted''' LiveCD root filesystem (conflicting with OpenVZ kernel packages and redundant packages - to free some disk space)
* Install OpenVZ kernels, tools and templates in '''booted''' LiveCD root filesystem
* Using <tt>mksquashfs</tt> 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 contains 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":
<pre>
# cd ~
# mkdir workbench
# cd workbench
</pre>

First of all we need some raw material - CentOS 4.4 LiveCD image:
<pre>
# 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
</pre>

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

You can see, that <tt>ovz-livecd/base/</tt> directory owns several *.mo files - images of squashfs filesystem,
and each image holds one directory of '''booted''' LiveCD root filesystem: <tt>bin</tt>, <tt>usr</tt> and so on:
<pre>
# ls -1 ovz-livecd/base
bin.mo etc.mo lib.mo root.mo sbin.mo usr.mo var.mo
</pre>

In order to decompress these images we need <tt>unsquashfs</tt> tool. <tt>squashfs</tt> source archive contains
patches for various kernel versions (to be able to mount <tt>squashfs</tt>) and user-space tools for compressing usual filesytem into <tt>squashfs</tt> filesystem and for decompressing it back. Well, we don't need kernel patches right now (but we will need them later), we only want to install <tt>squashfs</tt> user-space tools.
Here is '''an important''' note. We want, our LiveCD to be able to boot original Centos 4.4 kernel. This original kernel doesn't support
<tt>squashfs</tt> of version <tt>3</tt>. Consequently we use <tt>sqashfs2.2-r2</tt> for <tt>mksquasfs</tt> tool, but for <tt>unsquashfs</tt> tool and later for compiling fresh OpenVZ kernels with <tt>squashfs</tt> support we use <tt>sqashfs3.2-r2</tt> sources/patches, because they are back compatible with <tt>sqashfs v2</tt>.
<pre>
# wget http://belnet.dl.sourceforge.net/sourceforge/squashfs/squashfs2.2-r2.tar.gz
# tar xzf squashfs2.2-r2.tar.gz
# cd squashfs2.2-r2/squashfs-tools/
# make
cc mksquashfs.o read_fs.o sort.o -lz -o mksquashfs
# cp mksquashfs /usr/bin/

# cd ~/workbench/
# wget http://belnet.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 unsquashfs /usr/bin/
# cd ~/workbench
</pre>
Well, having the intruments in hand, why not extract the images? Create a directory, called <tt>livecd-root</tt>,
that will store the root filesystem of '''booted''' LiveCD. I.e. it will contain <tt>/bin</tt>, <tt>/sbin</tt>,
<tt>/etc</tt> and other directories, which you will see after booting the LiveCD. Unfortunately <tt>unsquashfs</tt>
tool is not very convenient, and I found only this way to use it:
<pre>
# 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
</pre>
Yet we have nearly complete root filesystem of '''booted''' LiveCD in <tt>livecd-root</tt> directory. However some things
are missing, and I guess you know what are they: <tt>/dev</tt>, <tt>/proc</tt>, <tt>/sys</tt>, <tt>/tmp</tt> and <tt>/boot</tt> directories. We need them, because some tools (<tt>rpm</tt>, <tt>bash</tt>, ...) will not work without them in chrooted environment later.
<pre>
# 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
</pre>

That's it. We have '''booted''' LiveCD root filesystem in <tt>livecd-root</tt> directory.
Now we can <tt>chroot</tt> 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 tool 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 <tt>squashfs</tt>. The next chapter explains how to create RPM-package with
OpenVZ kernel, that supports <tt>squashfs</tt>

=== Building OpenVZ kernels ===
Let's consider, how to build <tt>2.6.18</tt> OpenVZ kernel RPM-package with <tt>squashfs</tt> support.
First  download and install OpenVZ source RPM:
<pre>
# wget http://download.openvz.org/kernel/branches/2.6.18/028stab035.1/kernel-2.6.18-ovz028stab035.1.src.rpm
# rpm -ivh kernel-2.6.18-ovz028stab035.1.src.rpm
</pre>
<tt>squashfs</tt> sources contain the patch against <tt>2.6.18</tt>. Let's copy this patch to RPM build directory:
<pre>
# cp squashfs3.2-r2/kernel-patches/linux-2.6.18/squashfs3.2-patch /usr/src/redhat/SOURCES/
</pre>
Now we need to modify the spec-file (<tt>/usr/src/redhat/SPECS/kernel-ovz.spec</tt>) in order to add <tt>squashfs</tt> patch to build process. Below are the changes you should introduce in diff format.
The meaning of changes is transparent: firstly, do not build UP, enterprise and debug kernels (our LiveCD will be
based on SMP kernel) and secondly, apply <tt>squashfs</tt> patch before compilation.
<pre>
--- kernel-ovz.spec.orig        2007-06-09 11:40:15.000000000 +0400
+++ kernel-ovz.spec     2007-06-28 17:42:41.000000000 +0400
@@ -5,13 +5,13 @@ Summary: The Linux kernel (the core of t

 # normal/debug/debuginfo
 %define buildnormal 1
-%define builddebug 1
+%define builddebug 0
 %define builddebuginfo 0

 # kernels we want to build
-%define buildup 1
+%define buildup 0
 %define buildsmp 1
-%define buildenterprise 1
+%define buildenterprise 0
 %define buildentnosplit 0

 # versions
@@ -161,6 +161,9 @@ Patch2104: linux-2.6.18-drbd-0.7.22-0.8.
 Patch2105: linux-2.6.18-drbd-8.0.0-8.0.2.patch
 Patch2106: linux-2.6.18-drbd-8.0.2-8.0.3.patch

+# squashfs3.2-patch
+Patch2107: squashfs3.2-patch
+
 # ----------------------------------------------------------------------------

 BuildRoot: %{_tmppath}/kernel-%{KVERREL}-root
@@ -318,6 +321,8 @@ cd linux-%{kversion}
 %patch2105 -p1
 %patch2106 -p1

+%patch2107 -p1
+
 # ----------------------------------------------------------------------------

 mkdir configs
</pre>
We need one more tiny hack in order RPM-build process to walk smoothly.
There are config files for various OpenVZ kernel flavours 
in <tt>/usr/src/redhat/SOURCES</tt> directory:
<pre>
# ls /usr/src/redhat/SOURCES/*.config.ovz
/usr/src/redhat/SOURCES/kernel-2.6.18-i686.config.ovz             /usr/src/redhat/SOURCES/kernel-2.6.18-ppc64.config.ovz
/usr/src/redhat/SOURCES/kernel-2.6.18-i686-enterprise.config.ovz  /usr/src/redhat/SOURCES/kernel-2.6.18-x86_64.config.ovz
/usr/src/redhat/SOURCES/kernel-2.6.18-i686-smp.config.ovz         /usr/src/redhat/SOURCES/kernel-2.6.18-x86_64-smp.config.ovz
/usr/src/redhat/SOURCES/kernel-2.6.18-ia64.config.ovz
</pre>
'''All''' these files should contain information about <tt>squashfs</tt>.
In fact, only two additional lines are necessary:
<pre>
CONFIG_SQUASHFS=m
CONFIG_SQUASHFS_EMBEDDED=n
</pre>
I did it with the following command:
<pre>
# cd /usr/src/redhat/SOURCES/
# echo "CONFIG_SQUASHFS=m
> CONFIG_SQUASHFS_EMBEDDED=n" | tee -a *.config.ovz
CONFIG_SQUASHFS=m
CONFIG_SQUASHFS_EMBEDDED=n
</pre>
After all efforts, building the RPM-package is very easy:
<pre>
# cd /usr/src/redhat/SPECS/
# rpmbuild --target=i686 -ba kernel-ovz.spec
</pre>
If everything goes smoothly, in several tens of minutes depending on the power of your node you willl have OpenVZ kernel RPM-package with <tt>squashfs</tt> support. Let's copy it to our local directory <tt>to_booted_livecd/kernels/</tt>:
<pre>
# cd ~/workbench/
# ls /usr/src/redhat/RPMS/i686/
kernel-smp-2.6.18-ovz028stab035.1.i686.rpm
# mkdir -p to_booted_livecd/kernels
# cp /usr/src/redhat/RPMS/i686/kernel-smp-2.6.18-ovz028stab035.1.i686.rpm to_booted_livecd/kernels/
</pre>
OpenVZ LiveCD supports several kernels. So, the actions mentioned above should be accomplished to all kernels,
that you need on LiveCD. In this article I skip the description of building RPMS for all kernels. All description
below are based on <tt>028stab035</tt> kernel, that has been just build above. But some important differences in building
kernel of version other then 2.6.18 one is summarized below.
==== Peculiarities of building 2.6.9-rhel4 ====
* You should also include this path (http://git.openvz.org/?p=linux-2.6.18-openvz;a=commit;h=681d0b65dedd54d8c716cef56418ac1a478f94da)
in building process. Hopefully will be fixed in <tt>2.6.9-044stab044.8</tt> kernel.
* Use <tt>unionfs 1.0.14</tt>, but not <tt>unionfs 1.1.5</tt>, as offered at its official site!
* Small problems while building <tt>unionfs</tt>: arguments of <tt>vfs_permissions()</tt>. Just add <tt>NULL</tt>
to appropriate places.
==== Peculiarities of building 2.6.18-rhel5 ====
* Note, <tt>squashfs</tt> patch is already there, but you should use <tt>3.2</tt>! :)
* While building <tt>unionfs</tt> some small fixes: <tt>i_blksize</tt> field is missing in <tt>inode</tt> structure, <tt>ino_t</tt> should be changed to <tt>u64</tt> in some functions.

==== Peculiarities of building 2.6.20 ====
* FIXME

=== Unionfs kernel module ===
In most present-day LiveCDs <tt>unionfs</tt> filesystem is used. This filesystem "can appear to merge the contents of several directories, while keeping their physical content separate". For example, after the command
<pre>
# mount -t unionfs -o dirs=/tmp/changes=rw:/cdrom=ro unionfs /union
</pre>
you will see merged contents of <tt>/cdrom</tt> and <tt>/tmp/changes</tt> directories in <tt>/union</tt> directory. 
At that, <tt>cdrom</tt> will be read-only. I.e. if you will write to some file in <tt>/union</tt> directory, 
that resides in <tt>/cdrom</tt> in fact, this modified file will be automatically moved to <tt>/tmp/changes</tt>.
Such useful property is logically used in LiveCDs: <tt>unionfs</tt> merges cdrom contents (that is read-only)
and temporary in-memory filesystem.
In order to add support of <tt>unionfs</tt> filesystem to OpenVZ kernel we need to compile <tt>unionfs</tt> kernel
module against used kernel. Download the sources of unionfs:
<pre>
# wget ftp://ftp.filesystems.org/pub/unionfs/unionfs-1.x/unionfs-1.4.tar.gz
# tar xzf unionfs-1.4.tar.gz
</pre>
In previous chapter we have created an RPM-package with OpenVZ kernel. We should install it: because
this packages contents kernel headers, required for building kernel modules.
<pre>
# rpm -ivh to_booted_livecd/kernels/kernel-smp-2.6.18-ovz028stab035.1.i686.rpm 
Preparing...                ########################################### [100%]
   1:kernel-smp             ########################################### [100%]
</pre>
Now compile <tt>unionfs</tt>:
<pre>
# cd unionfs-1.4
# echo 'LINUXSRC=/lib/modules/2.6.18-ovz028stab035.1-smp/build/
> TOPINC=-I$(LINUXSRC)/include
> MODDIR=/lib/modules/2.6.18-ovz028stab035.1-smp/' > fistdev.mk
# make
# ls unionfs.ko 
unionfs.ko
# cd ..
</pre>
Later we will place <tt>unionfs.ko</tt> to appropriate place in '''booted''' LiveCD filesystem.
At the moment copy it to local <tt>to_booted_livecd/unionfs-modules/2.6.18/</tt> directory:
<pre>
# mkdir -p to_booted_livecd/unionfs-modules/2.6.18/
# cp unionfs-1.4/unionfs.ko to_booted_livecd/unionfs-modules/2.6.18/
</pre>
I repeat once again: if you want to use several kernels on LiveCD - the operation above should
be repeated for each wishful kernel.

=== OpenVZ tools and templates. CentOS updates ===
We have now the kernel RPM-package. But we also need OpenVZ tools RPM-packages.
It is much easier with them: just download these packages from http://openvz.org:
<pre>
# mkdir to_booted_livecd/tools
# cd to_booted_livecd/tools/

# wget http://download.openvz.org/utils/vzctl/3.0.16/vzctl-3.0.16-1.i386.rpm
# wget http://download.openvz.org/utils/vzctl/3.0.16/vzctl-lib-3.0.16-1.i386.rpm
# wget http://download.openvz.org/utils/vzquota/3.0.9/vzquota-3.0.9-1.i386.rpm
# wget http://download.openvz.org/template/utils/vzpkg/2.7.0-18/vzpkg-2.7.0-18.noarch.rpm
# wget http://download.openvz.org/template/utils/vzrpm43/current/vzrpm43-4.3.3-7_nonptl.6.i386.rpm
# wget http://download.openvz.org/template/utils/vzrpm43/current/vzrpm43-python-4.3.3-7_nonptl.6.i386.rpm
# wget http://download.openvz.org/template/utils/vzrpm44/current/vzrpm44-4.4.1-22.5.i386.rpm
# wget http://download.openvz.org/template/utils/vzrpm44/current/vzrpm44-python-4.4.1-22.5.i386.rpm
# wget http://download.openvz.org/template/utils/vzyum/current/vzyum-2.4.0-11.noarch.rpm

# mkdir ../template-metadatas
# cd ../template-metadatas

# wget http://download.openvz.org/template/metadata/centos-4/vztmpl-centos-4-2.0-2.i386.rpm
# wget http://download.openvz.org/template/metadata/fedora-core-3/vztmpl-fedora-core-3-2.0-2.i386.rpm
# wget http://download.openvz.org/template/metadata/fedora-core-4/vztmpl-fedora-core-4-2.0-2.i386.rpm
# wget http://download.openvz.org/template/metadata/fedora-core-5/vztmpl-fedora-core-5-2.0-2.i386.rpm

# mkdir ../precreated
# cd ../precreated

# wget http://download.openvz.org/template/precreated/centos-4-i386-minimal.tar.gz
# wget http://download.openvz.org/template/precreated/debian-3.1-i386-minimal.tar.gz
# wget http://download.openvz.org/template/precreated/fedora-core-5-i386-minimal.tar.gz

# cd ~/workbench/
</pre>
As you understand, you can add other precreated templates to LiveCD. The main thing here is that usual CD is 
not rubber and precreated templates are rather big! ;)

Centos 4.4 LiveCD has a serios problem: <tt>sqlite</tt> package is broken and consequently
<tt>yum</tt> doesn't work. In order to fix this problem we need updated <tt>sqlite</tt> package:
<pre>
# mkdir to_booted_livecd/updates
# cd to_booted_livecd/updates
# wget http://centos.arcticnetwork.ca/4.5/os/i386/CentOS/RPMS/sqlite-3.3.6-2.i386.rpm
# cd ~/workbench/
</pre>

=== Install all these finally ===
We have all components that will be on '''booted''' LiveCD ready. Let's install them
in <tt>chrooted</tt> environment. But before uninstall <tt>lsctp-tools</tt> package,
because these tools need kernel version prior to 2.6.10. Then update <tt>sqlite</tt>
package. Also we need to remove some other packages in order to free some disk space:
I've removed <tt>openoffice.org</tt>, <tt>gimp</tt>, <tt>dia</tt>, <tt>gnome-games</tt>,
<tt>tetex</tt>, <tt>latex</tt>, <tt>k3b</tt> and printing related packages:
<pre>
# cp -r to_booted_livecd/ root/tmp/
# chroot root/

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

# rpm -e openoffice.org-libs openoffice.org
# rpm -e gimp-data-extras xsane-gimp gimp-print-plugin gimp-print-utils
# rpm -e gimp gimp-print gimp-help gimp-gap
# rpm -e dia
# rpm -e planner
# rpm -e gnome-games
# rpm -e tetex-latex jadetex xmltex passivetex tetex tetex-afm \
tetex-dvips tetex-fonts tetex-xdvi
# rpm -e k3b
# rpm -e foomatic Omni Omni-foomatic system-config-printer \
system-config-printer-gui hal-cups-utils desktop-printing

# cd /tmp/to_booted_livecd/

# rpm -Uvh updates/sqlite-3.3.6-2.i386.rpm

# rpm -ivh kernels/kernel-smp-2.6.18-ovz028stab035.1.i686.rpm 
# rpm -ivh tools/*.rpm
# rpm -ivh template-metadatas/*.rpm
</pre>

Copy precreated templates to appropriate place:
<pre>
# cp  precreated/* /vz/template/cache/
</pre>
Add <tt>unionfs.ko</tt> to other kernel modules and run <tt>depmod</tt>:
<pre>
# mkdir /lib/modules/2.6.18-ovz028stab035.1-smp/kernel/fs/unionfs
# cp unionfs-modules/2.6.18/unionfs.ko /lib/modules/2.6.18-ovz028stab035.1-smp/kernel/fs/unionfs/
# depmod 2.6.18-ovz028stab035.1-smp
# exit
exit
</pre>
While being in chrooted environment bash history was written to <tt>~/.bash_history</tt> file.
Clean it:
<pre>
# rm root/root/.bash_history
</pre>
Here we have to make one step to workaround [[Checkpointing and live migration]] problem. The thing is that at the moment
chekpointing isn't supported on <tt>unionfs</tt> filesystem ([http://bugzilla.openvz.org/show_bug.cgi?id=606  Bug #606]).
But we want of course checkpoiting to work on LiveCD. If we mount <tt>tmpfs</tt> on <tt>/vz/private/</tt> on '''booted''' LiveCD,
then all newly created VEs reside on <tt>tmpfs</tt> and checkpointing works. Moreover we do not introduce any additional memory usage,
because even without <tt>tmpfs</tt> all VEs reside in RAM (they contain new/updated files for <tt>unionfs</tt>).

Create <tt>/vz/private</tt> directory, later, while modifying initrd image we will add the line that will mount <tt>tmpfs</tt>
on this directory:
<pre>
mkdir root/vz/private/
</pre>
At the moment vzquota doesn't support <tt>tmpfs</tt> ([http://bugzilla.openvz.org/show_bug.cgi?id=558  Bug #558]).
We're working on this problem, but for now '''switching the disk quota off''' in <tt>/etc/vz/vz.conf</tt>: <tt>DISK_QUOTA=no</tt>.
But when disk quota is off <tt>vzmigrate</tt> fails! ;) This is the [http://bugzilla.openvz.org/show_bug.cgi?id=558  Bug #512].
So, don't forget to apply the patch attached to this bug report to <tt>vzmigrate</tt>.

'''Booted''' LiveCD filesystem is ready, congratulations!

=== Compressing '''booted''' LiveCD filesystem ===
Since <tt>mksquashfs</tt> tool is already installed we can simply use it to create
<tt>*.mo</tt> files: 
<pre>
# rm -f ovz-livecd/base/*.mo
# mksquashfs root/lib/ ovz-livecd/base/bin.mo -keep-as-directory
# mksquashfs root/etc/ ovz-livecd/base/etc.mo -keep-as-directory
# mksquashfs root/lib/ ovz-livecd/base/lib.mo -keep-as-directory
# mksquashfs root/root/ ovz-livecd/base/root.mo -keep-as-directory
# mksquashfs root/sbin/ ovz-livecd/base/sbin.mo -keep-as-directory
# mksquashfs root/usr/ ovz-livecd/base/usr.mo -keep-as-directory         # it can take long...
# mksquashfs root/var/ ovz-livecd/base/var.mo -keep-as-directory
# mksquashfs root/vz/ ovz-livecd/base/vz.mo -keep-as-directory
</pre>

=== Vmlinux, initrd and isolinux.cfg ===
The next step is to force <tt>isolinux</tt> (cdrom boot loader) to boot OpenVZ kernel.
First, copy kernel image to OpenVZ CD. It is important to give '''short name''' (not greater
than 8 characters) to kernel image, otherwise <tt>isolinux</tt> will not see it.
<pre>
# cp root/boot/vmlinuz-2.6.18-ovz028stab035.1-smp ovz-livecd/boot/ovz18
</pre>
Modify initrd image. More precisely, we need to add OpenVZ kernel modules there
and apply small patches to <tt>liblinuxlive</tt> file. Initrd image that goes with Centos 4.4 is
of size 40Mb. OpenVZ LiveCD will contain several kernels, so initrd should have several sets of
kernel modules (for each kernel) and 40Mb isn't enough in this case. I created an initrd of size 100Mb.
Don't forget to update <tt>ramdisk_size</tt> in <tt>isolinux.cfg</tt> file later!

Creating "big" initrd with original content:
<pre>
# mkdir initrd.d
# cp ovz-livecd/boot/initrd.gz initrd.d/initrd-old.gz
# cd initrd.d/
# mkdir mount-old
# gunzip initrd-old.gz 
# mount -o loop initrd-old mount-old/
# dd if=/dev/zero of=initrd bs=1048576 count=100
# mkdir mount
# mount -o loop initrd mount/
# cp -a mount-old/* mount/
# umount mount-old/
# rm -rf mount-old initrd-old
</pre>
Copy modules to initrd:
<pre>
# cp -r ../root/lib/modules/2.6.18-ovz028stab035.1-smp/ mount/lib/modules/
# rm -rf mount/lib/modules/2.6.18-ovz028stab035.1-smp/build                 # we don't neet it on initrd image
</pre>
initrd image, that goes with Centos 4.4 LiveCD doesn't load cdrom kernel modules.
It works well for CentOS kernel, because cdrom support is built-in there.
But OpenVZ kernel supports cdrom (usual ide cdrom) via kernel module.
Consequetnly we need to apply the following patch to <tt>liblinuxlive</tt> file:
<pre>
--- liblinuxlive.orig   2006-08-19 08:53:11.000000000 +0400
+++ liblinuxlive        2007-07-02 17:50:34.000000000 +0400
@@ -337,6 +337,9 @@ modprobe_essential_modules()
 {
    echolog "starting loop device support"
    modprobe_module loop max_loop=32
+   echolog "starting cdrom support"
+   modprobe_module cdrom
+   modprobe_module ide-cd
    echolog "starting cdrom filesystem support"
    modprobe_module isofs
    echolog "starting squashfs support"
</pre>
As mentioned earlier we want to mount <tt>tmpfs</tt> on /vz/private automatically. Just apply this patch to
<tt>liblinuxlive</tt> file:
<pre>
--- liblinuxlive.orig-fstab     2007-07-02 17:50:34.000000000 +0400
+++ mount/liblinuxlive  2007-07-03 12:33:30.000000000 +0400
@@ -414,6 +414,7 @@ activate_fstab()
    echo "tmpfs            /                tmpfs       defaults         0   0" >$FSTAB
    echo "devpts           /dev/pts         devpts      gid=5,mode=620   0   0" >>$FSTAB
    echo "proc             /proc            proc        defaults         0   0" >>$FSTAB
+   echo "tmpfs            /vz/private      tmpfs       defaults         0   0" >>$FSTAB

    # now done by fstab-sync
    # list_cdrom_devices | while read DEVICE; do
</pre>
Finishing actions with initrd:
<pre>
# sync
# umount mount/
# gzip initrd
# /bin/cp initrd.gz ../ovz-livecd/boot/initrd.gz
# cd ..
</pre>
Now we should modify <tt>ovz-livecd/isolinux.cfg</tt> file, that controls <tt>isolinux</tt> boot loader.
We inform boot loader, that new kernel was added by introducing the following changes (in diff format):
<pre>
--- ovz-livecd/isolinux.cfg.orig   2006-08-19 08:53:09.000000000 +0400
+++ ovz-livecd/isolinux.cfg     2007-07-02 19:10:51.000000000 +0400
@@ -1,5 +1,5 @@
 display boot/splash.cfg
-default linux
+default ovz18
 prompt 1
 timeout 300
 F1 boot/help1.txt
@@ -11,5 +11,9 @@ label linux
 kernel boot/vmlinuz
 append max_loop=32 vga=791 initrd=boot/initrd.gz init=linuxrc load_ramdisk=1 prompt_ramdisk=0 ramdisk_size=40000 root=/dev/ram0 rw rhgb quiet

+label ovz18 
+kernel boot/ovz18
+append max_loop=32 vga=791 initrd=boot/initrd.gz init=linuxrc load_ramdisk=1 prompt_ramdisk=0 ramdisk_size=102400 root=/dev/ram0 rw rhgb
+
 label memtest
 kernel boot/memtest

</pre>

Also '''don't forget''' to change <tt>ramdisk_size</tt> to 102400 for all kernels including Centos 4.4 default! 

And I suggest to remove <tt>quite</tt> parameter, to see what happens: it will help greatly if some problem will happen.

=== Embellishment ===
If you want to release LiveCD to other people some "embelishments" should be added.

First, edit <tt>splash.cfg</tt>, <tt>help1.txt</tt>, <tt>help2.txt</tt> and <tt>help3.txt</tt>
files (that are in <tt>~/workbench/ovz-livecd/boot/help</tt> directory) to contain appropriate information.
These messages appear on the LiveCD initial boot: they help to choose kernel and kernel options.

Also, you can note, that CentOS logo appears at this moment. This logo resides in <tt>ovz-livecd/boot/splash.lss</tt>
file. I added OpenVZ logo there. The following tools will help you: <tt>lss16toppm</tt>, <tt>ppmtolss16</tt> and
of course <tt>gimp</tt> :)

One more thing we change is default desktop background. It resides in <tt>usr/share/backgrounds/images/default.png</tt>.
I added OpenVZ logo there.

=== Creating ISO ===
Centos 4.4 LiveCD creators were very gentle and have placed <tt>make_iso.sh</tt> script on CD.
Using this script, it is very easy to create iso:
<pre>
# cd ovz-livecd
# ./make_iso.sh ../CentOS-4.4-i386-OpenVZ-LiveCD.iso
</pre>

== Debugging LiveCD ==
If you have trouble with created OpenVZ LiveCD, boot the kernel with
<pre>
vga=0 debug
</pre>
command line options. It will help you to diagnose the problem more precisely.
Also it can be useful to redirect kernel output to serial console:
<pre>
console=ttyS0,115200 console=tty
</pre>

== External Links ==
* [http://centos.org Official CentOS community website]
* [http://kernel.org Linux kernel website]
* [http://redhat.com RedHat Inc. website]
* [http://squashfs.sourceforge.net/ squashfs website]
* [http://www.filesystems.org/project-unionfs.html uninonfs official homepage]