This page describes how to customize the Ubuntu Dekstop CD. This is typically done to showcase certain packages that don't come with the default Ubuntu CD. This information is based on Ubuntu 8.04 and may or may not be applicable to future releases.
Brief overview of the process
An extremely general picture is: unpack stuff from CD, add our packages, pack it all back. Now a little more detail on each part.
- The whole filesystem of the Ubuntu that will run in the Live session is packed into a single file on the CD. This file is
/casper/filesystem.squashfs
and one needs thesquashfs
kernel module to work with such filesystems. - One needs to prepare packages (.deb files) that are to be added to the system. These packages may have dependencies that also need to be downloaded beforehand.
- The final CD image may turn up to be more than 700MB after we add our stuff. So some sacrificing of other useless contents might be needed after we add our packages.
- There are tricks to pack everything back. They all will be explained below in their respective order.
Unpacking
This part is by far the easiest. Once you have downloaded the original iso file with the Ubuntu desktop CD, mount it:
mount ubuntu-8.04-desktop-i386.iso mnt -o loop
assuming that you have an empty directory mnt
and the iso file in your working directory. Then copy everything into another directory using rsync
:
rsync --exclude=/casper/filesystem.squashfs -a mnt/ iso
This will create the directory called iso
with the contents of the CD, except for the largest file /casper/filesystem.squashfs
that holds the whole target filesystem.
Next we unpack the target filesystem from that huge file. First we will mount it using another empty directory mnt_sq
:
mount mnt/casper/filesystem.squashfs mnt_sq -o loop -t squashfs
And then we rsync
from it to a new directory:
rsync -a mnt_sq/ squash
This should create the directory squash
with the contents of the target filesystem. Now that we are done with the mounted images, we may unmount them:
umount mnt_sq umount mnt
At this point you should have the directory iso
with all the contents on the CD needed for booting the Ubuntu system, and the directory squash
with the system itself.
Adding our packages
For the sake of simplicity, let's assume that you have collected all the packages you want to add in a separate directory new/debs
relative to your working directory. That is, there's new
dir with the subdir debs
where all the deb packages are collected. Let's copy all these packages onto the target filesystem (any place will do for now, but I chose /root
):
cp new/debs/* squash/root/
Then we will prepare chroot
environment like so:
mount -t proc proc squash/proc mount -t sysfs sysfs squash/sys
and then we will "change root" (chroot
) to that target filesystem and install packages.
chroot squash dpkg -i /root/gramps_3.0.1-1_all.deb
Changing root means we will see only the target filesystem as if we were trully running it it and it were our root filesystem. So the above command changes root to squash
and then runs dpkg -i /root/gramps_3.0.1-1_all.deb
command to install GRAMPS.