To Create a Live Linux CD/DVD

A live CD is a bootable CD that contains the whole operating system and any applications you want to run from the CD. With the increasing popularity of DVD and Blu-ray drives, there is even a live DVD. A live CD is useful when you want to copy your existing Linux system to a CD and run it on multiple computers. In this post, I show how I normally create a live CD.

Rebuild a kernel with SquashFS and UnionFS patch

A new kernel should be built with SquashFS and UnionFS patches. The live CD will have a huge file that is actually a SquashFS image containing a copy of your existing Linux system. We will use UnionFS so that any changes to the read-only SquashFS will be saved to the volatile memory. Download the patches from the following locations.

• squashfs.sourceforge.net
  
• unionfs.filesystems.org
  

After patching the kernel and rebuilding it, install the new kernel.

Make a SquashFS image of an existing Linux system

A SquashFS image needs to be created from an existing Linux system. Copy the contents of the Linux filesystem to an empty directory, assuming the filesystem is mounted at /mnt.

mkdir /tmp/livecd
cd /mnt
tar cf - . | (cd /tmp/livecd; tar xf -)

Empty the contents of fstab so that the live CD will not mount any hard disk partition, including the original root partition.

cp /dev/null /tmp/livecd/etc/fstab

Create a squashfs image.

mksquashfs /tmp/livecd /tmp/linuxfs.sqz -comp xz -b 262144 -Xdict-size 196608 -no-xattrs -e boot lost+found selinux srv

Create a Custom InitRamFS image

This is a tricky part of the job. Basically, the init script of the initramfs image will mount the CD-ROM, then mount the SquashFS image, and then mount a UnionFS. Refer to this post on building an initramfs image.

Create a Live CD structure.

Create an empty directory which will be the contents of live CD. The live CD will contain:

• SquashFS image (named linuxfs.sqz, for example)
  
• isolinux.bin and isolinux.cfg
  
• kernel
  
• initramfs image
  

Finally, create an ISO image for the live CD.

genisoimage -V LIVECD -b isolinux.bin -c boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table /tmp/isofs > ~/livecd.iso

Burn the ISO image.

cdrskin -v dev=/dev/sr0 speed=8 driveropts=burnfree ~/livecd.iso