This CD is based of CentOS 4.3 (http://www.centos.org)
In addition to CentOS packages file system driver’s unionfs, SquashFS and boot loader ISOLINUX 3.11 is used.



A list of mirrors where the source code of CentOS can be found here:
http://www.centos.org/modules/tinycontent/index.php?id=13

Direct link to CentOS source code:
http://mirrors.kernel.org/centos/4.3/os/SRPMS/


Source Code for unionfs and SquashFS can be found on the following locations:

SquashFS - http://squashfs.sourceforge.net
unionfs - http://www.fsl.cs.sunysb.edu/project-unionfs.html

Source Code for ISOLINUX can be found here:
http://www.kernel.org/pub/linux/utils/boot/syslinux/

----------------------------------------


A quick How-To describing how this CD came to life:

This how-to is heavily based on this Gentoo LiveCD how-to - http://forums.gentoo.org/viewtopic-t-410389.html


First a short description on how the CD works:

	- Boot a Linux kernel and load an initial ram disk.
	- Execute linuxrc script in initial ram disk.
	- linuxrc will mount the CD.
	- linuxrc will mount a squashfs file system
	- linuxrc will unify the squashfs read only file system with a read write tmpfs.
	- linuxrc will execute init, and CentOS should load.


And now some more details:

NOTE! I wrote this how-to from memory; it is possible that I have missed something.


1. First you need to install a build/development environment; I used CentOS 4.3 and chose to install all development packages.

2. You need to install the Kernel Source Code.

 	Obtain the kernel-<version>.src.rpm file from one of the following
	Sources:

	- The SRPMS directory on the appropriate "SRPMS" CD ISO image
	- The FTP site where you got the kernel package
	- By running the following command:	
	
	bash# 	up2date --get-source kernel

Install kernel-<version>.src.rpm (given the default RPM configuration, the files this package contains will be written to /usr/src/redhat/)

Change directory to /usr/src/redhat/SPECS/, and issue the following command:	

	bash# 	rpmbuild -bp --target=<arch> kernel.spec

(Where <arch> is the desired target architecture.)

On a default RPM configuration, the kernel tree will be located in /usr/src/redhat/BUILD/.

In resulting tree, the configurations for the specific kernels shipped in Red Hat Enterprise Linux 4 are in the /configs/ directory. For example, the i686 SMP configuration file is named /configs/kernel-<version>-i686-smp.config. Issue the following command to place the desired configuration file in the proper place for building:

	bash# 	cp <desired-file> ./.config


3. We need to add SquashFS support.

Download SquashFS from: http://squashfs.sourceforge.net

First patch the kernel source code:

(http://www.artemio.net/projects/linuxdoc/squashfs/SquashFS-HOWTO.html#preparing)

Change to the SquashFS source directory and copy the kernel patch (we'll assume it's named squashfs-patch) to /usr/src/linux. 

	bash# 	cd /usr/src/squashfs
	bash# 	cp linux-2.x.y/squashfs-patch /usr/src/linux

Go to the Linux kernel source directory /usr/src/linux: 

	bash# 	cd /usr/src/linux

Note: please remember that we will not be leaving this directory during all further kernel-related procedures, and all paths will be given relative to /usr/src/linux.

Now patch the source with the SquashFS patch:

	bash# 	patch -p1 < squashfs-patch


Second we need to compile and install the mksquashfs tool:

(http://www.artemio.net/projects/linuxdoc/squashfs/SquashFS-HOWTO.html#mksquashfs)

	bash# 	cd /usr/src/squashfs/squashfs-tools

Compile and install mksquashfs: 

	bash# 	make
	bash# 	cp mksquashfs /usr/sbin

If everything went fine, typing mksquashfs at the shell prompt should print its "usage" message. 

4. To compile the Kernel change directory to the location of the source code and run the following commands:

	bash#	make oldconfig
	
	Answer YES to add SqushFS support.	

	bash#	make menuconfig

	I made changes so ext3 support is built into the kernel instead of a kernel module which is default.
	You will need to build a kernel with support for your hardware so that it can boot without and initrd.

	bash#	make
	bash#	make install

5. We need to reboot using our newly built kernel.

Copy the new bzImage into /boot and edit your boot loader configuration. Reboot.

6. We need to add unionfs support.

Getting unionfs to play with CentOS was a bit unpleasant. In the later versions of unionfs it is possible to patch the kernel sources to add unionfs support, this however does not work with the CentOS Kernel sources. In addition the later versions also failed when I tried to compile them as modules. In the end I found that the most recent version of unionfs that I could get to play with CentOS is unionfs-1.0.9.

Download: unionfs-1.0.9.tar.gz from ftp://ftp.fsl.cs.sunysb.edu/pub/unionfs/

Extract the archive and run the following commands:

	bash#	make
	bash#	make install
	bash# 	depmod -a

To check that the unionfs module was successfully build run commands:

	bash# 	modprobe unionfs
	bash#	dmesg

7. We need to install OMSA on the develop/build install to compile driver modules for our kernel

Run the following command to install OMSA:
	
	bash#	wget -q -O - http://linux.dell.com/yum/software/bootstrap-omsa-all.sh | bash
	bash#	OMIIGNORESYSID=1 up2date -i srvadmin-all

(I use OMIIGNORESYSID=1 because I made this CD using VMWare which is not a supported system. If you create the CD on a Power Edge System this should not be necessary.)


To Compile the OMSA driver modules I did the following:

Edit the /etc/init.d/instsvsdrv script:

Comment out this line: 
	
	SYS_TYPE=$1

Add this directly below the line we comment out:

	SYS_TYPE=0

Now to compile the dcdbas driver only:

	bash#	/etc/init.d/instsvcdrv start
	bash#	/etc/init.d/instsvcdrv stop

Edit /etc/init.d/instsvsdrv again:

Change 	SYS_TYPE=0 to SYS_TYPE=1

Then to compile the dcdtvm driver do:

	bash#	/etc/init.d/instsvcdrv start
	bash#	/etc/init.d/instsvcdrv stop


Repeat above action setting SYS_TYPE=2 and SYS_TYPE=4 as well.

SYS_TYPE=2 will compile dcdesm driver.
SYS_TYPE=4 will compile dcdipm driver.


********* 
NOTE!!!!!

After SYS_TYPE=4 (dcdipm driver) do not run bash# /etc/init.d/instsvcdrv stop

In VMware unloading the dcdipm drive module cause a kernel panic.
*********



****** We have now built the kernel and the kernel modules we need to make our live CD. 
****** Next up is installing minimal CentOS onto a second partition or hard drive.


8. Install CentOS 4.3, use the GUI installer. (Will refer to this install as "LiveCD Install" later)

 - I installed a custom system with no SElinux, and choose "minimal" at package selection.
 I created the following partitions during install:
	/boot
	/
	swap

9. After the install, configure the system to use the Dell yum repository, and update the system:

	bash#	wget -q -O - http://linux.dell.com/yum/software/bootstrap.sh | bash
	bash# 	rpm --import /usr/share/rhn/RPM-GPG-KEY
	bash#	up2date -u

10. To install X and Gnome Run the following commands:

	bash#	up2date -i system-config-display
	bash#	up2date -i gnome-session

11. We need to copy the kernel modules for our custom kernel over from the development/build system.

Reboot into the development/build system, mount the minimal root (/) partition of the minimal install.

	bash# mount /dev/hdb3 /mnt/livecd

Copy the custom-kernel modules over to the livecd install:
	
	bash# cp -a /lib/modules/<custom-kernel> /mnt/livecd/lib/modules/

Remove the kernel modules for the default-centos-kernel:
	
	bash# rm -rf /mnt/livecd/lib/modules/<default-centos-kernel>

12. We need to install OMSA on the "liveCD Install".

Reboot into the "liveCD Install".

Run the following command to install OMSA:

	bash#	wget -q -O - http://linux.dell.com/yum/software/bootstrap-omsa-all.sh | bash
	bash#	OMIIGNORESYSID=1 up2date -i srvadmin-all

(I use OMIIGNORESYSID=1 because I made this CD using VMWare which is not a supported system. If you create the CD on a Power Edge System this should not be necessary.)

I choose to configure the CD no to auto start OMSA services:

	bash# chkconfig instsvcdrv off
	bash# chkconfig dataeng off
	bash# chkconfig omsad off
	bash# chkconfig omawsd off


13. Cleanup the startup, faster boot and some services fail to start from the CD.

(I do not remember exactly what services I turned off; here is a short list to give you a general idea.)

	bash# chkconfig smartd off
	bash# chkconfig sendmail off
	bash# chkconfig cron off
	bash# chkconfig anacron off
	bash# chkconfig kudzu off
	bash# chkconfig isdn off

14. To make networking work on all systems 

We need to edit the following file:

	/etc/sysconfig/network-scripts/ifcfg-eth0

Remove the line with the MAC address.


15. To Auto configure X and automatically start a GNOME session

Edit the following file:

	/etc/rc.local

Add the following:

	echo "Trying to auto configure X"
	system-config-display --noui --reconfig --set-resolution=1024x768

	echo "Starting X and GNOME"
	startx

16. To help the initrd we need to move chroot from to /bin

	bash# 	mv /usr/sbin/chroot /bin

(I believe it is located in /usr/sbin/ as default, if not look in /sbin or /usr/bin)


17. Install any additional software you want, add any configuration changes that you want etc.

When you have done all the changes you want, reboot into the build/development install.



18. We need to populate /dev on the "liveCD install" root partition.

	bash# mount /dev/hdb3 /mnt/livecd
	bash# tar xvzf dev.tar.gz -C /mnt/livecd/

19. We need to edit /etc/fstab on the "liveCD install"

The /etc/fstab file should include only the following:

	unionfs			/		unionfs 	defaults    	0 0
	none                    /dev/pts        devpts  	gid=5,mode=620  0 0
	none                    /dev/shm        tmpfs   	defaults        0 0
	none                    /proc           proc    	defaults        0 0
	none                    /sys            sysfs   	defaults        0 0




20. Creating the initrd


First we create an image file, put an ext2 file system on it and mount it a loop device.

	bash#	dd if=/dev/zero of=initrd BS=1M count=8
	bash#	mke2fs initrd
	bash#	mkdir /mnt/loop
	bash#	mount -o loop initrd /mnt/loop

Now we need to create the files and directories we need in our initial ram disk.

	bash#	mkdir etc dev lib bin proc new cdrom static dynamic union
	bash#	touch linuxrc 
	bash#	chmod +x linuxrc 
	bash#	touch etc/mtab 
	bash#	touch etc/fstab

Then we need to copy the files, binaries, libraries and kernel modules that we need in our initial ram disk.

Files that go in /mnt/loop/bin (The initrd /bin directory)

	cat  
	chroot  
	insmod  
	mkdir  
	mount  
	pivot_root  
	sh  
	tar  
	umount

To figure out what files should go in /mnt/loop/lib (The initrd /lib directory) use the ldd command.

Example: 	bash# 	ldd /bin/sh 

Will output:
		linux-gate.so.1 =>  (0xffffe000) 
		libreadline.so.5 => /lib/libreadline.so.5 (0xb7f72000) 
		libhistory.so.5 => /lib/libhistory.so.5 (0xb7f6b000) 
		libncurses.so.5 => /lib/libncurses.so.5 (0xb7f33000) 
		libdl.so.2 => /lib/libdl.so.2 (0xb7f2f000) 
		libc.so.6 => /lib/libc.so.6 (0xb7e42000) 
		/lib/ld-linux.so.2 (0xb7fad000)

So, sh need the above list of libraries to run, copy them into place. 

NOTE! Ignore linux-gate.so.1


In addition to this wee need to copy our unionfs drive module and the modules.dep file into /lib

	bash#	cp /lib/modules/<custom-kernel>/kernel/fs/unionfs.ko /mnt/loop/lib
	bash#	cp /lib/modules/<custom-kernel>/modules.dep /mnt/loop/lib


Populate the /dev directory in our initial ram disk:

	bash#	mknod /mnt/loop/dev/console c 5 1 
	bash#	mknod /mnt/loop/dev/null c 1 3 
	bash#	mknod /mnt/loop/dev/hda b 3 0 
	bash#	mknod /mnt/loop/dev/hdb b 3 64 
	bash#	mknod /mnt/loop/dev/hdc b 22 0 
	bash#	mknod /mnt/loop/dev/hdd b 22 64 
	bash#	mknod /mnt/loop/dev/tty c 4 0 
	bash#	mknod /mnt/loop/dev/loop0 b 7 0


Create/Edit the linuxrc script that will find the CD, mount the file systems and execute init in the end:

	#!/bin/sh         

	export PATH=/bin                

	for x in hda hdb hdc hdd                        
	do  
        	mount -t iso9660 /dev/${x} /cdrom                                         
	        if [ "$?" == "0" ]                          
	        then            
	                CDROM=${x}                          
	                break                     
	        fi          
	done    

	if [ "${CDROM}" == "" ]                       
	the  
	        echo "FATAL --- LIVECD NOT FOUND"                                         
	        exec /bin/sh                    
	        exit            
	fi  

	echo "LiveCD found in /dev/${CDROM}"                                    

	/bin/insmod /lib/unionfs.ko                           

	mount -t squashfs -o loop /cdrom/livecd.squashfs /static
	mount -t tmpfs -o size=300M none /dynamic
	mount -t unionfs -o dirs=/dynamic=rw:/static=ro unionfs /union

	cd /union

	/bin/pivot_root . initrd

	mount --move /initrd/dynamic /mnt/dynamic
	mount --move /initrd/static /mnt/static
	mount --move /initrd/cdrom /mnt/cdrom
	mount -t tmpfs -o size=50M none /tmp

	mount -t proc none /proc
	cat /proc/mounts > /etc/mtab
	umount /proc

	exec chroot . /bin/sh <<- EOF >dev/console
	umount /initrd
	echo "Starting init!"
	exec /sbin/init
	EOF



Finally we need to unmount the initrd, and compress it with gzip.

	bash# ummount /mnt/loop
	bash# gzip initrd



21. We need to copy out bzImage, ISOLINUX and initrd into what will be the BOOT directory on the CD

	bash# 	mkdir boot
	bash#	mkdir isolinux
	bash#	cp <path-to-isolinux.bin> boot/isolinux/
	bash#	touch boot/isolinux/isolinux.cfg
	bash# 	cp initrd.gz boot/isolinux/	
	bash#   cp bzImage boot/isolinux/livekrnl

22. Edit the isolinux.cfg file, my isolinux.cfg file look like this:

	timeout 1
	default Linux

	label Linux
		kernel livekrnl
		append initrd=initrd.gz init=/linuxrc root=/dev/ram0



23. Preparing the CDROOT directory

	bash# 	mkdir cdroot
	bash#	cp -a boot cdroot/
	
24. Creating the SquashFS file system

	bash#	cd cdroot/
	bash#	mksquashfs /mnt/livecd livecd.squashfs
	bash#	cd ..

25. Create a bootable CD ISO image using mkisofs

	bash# 	mkisofs -R -b boot/isolinux/isolinux.bin -no-emul-boot -boot-load-size \ 
		4 -boot-info-table -c boot/isolinux/boot.cat -iso-level 3 -o livecd.iso cdroot/





Once this ISO I created it is time to burn it to a CD and test it.



To save space I also spent some time deleting documentation files and the rpm database etc.