Create Custom liveCD

Date: 2012-11-19

This are the scripts used to create a live cd for the SensLab platform.

Githubers interest is the content of the scripts and the problems I got and how they got solved. The scripts will likely not be maintained in the future.

Creating a customized livecd

Execute the scripts in the following order

1-unpack_iso.sh
2-chroot.sh
- From the chrooted environment:
- run your personal update commands
- /chroot_install_folder/script_run_as_chroot.sh
3-copy_static_files.sh
4-repack_iso.sh

Personalization, what to do before using

Update the common.source to set the correct livecd url and the directories
Personalize the content of chroot_install_folder/script_run_as_chroot.sh
Personalize the content of 3-copy_static_files.sh
Add files to copy on the livecd in root folder. Files in root/etc/skel will be copied in the user home directory.
Update the version of chroot_install_folder/VBoxLinuxAdditions.run

Blocking steps

I updated the documentation on the Ubuntu English and French wikis to correct errors I got. So errors mentioned here are already solved in the documentation.

casper.conf

The documentation on liveCDcustomization used an out of date /etc/casper.conf and did not mention the FLAVOUR command that must be set in order to take the other variables into account.

It should be set to something

# This file should go in /etc/casper.conf
# Supported variables are:
# USERNAME, USERFULLNAME, HOST, BUILD_SYSTEM, FLAVOUR

export USERNAME="custom-username"
export USERFULLNAME="Live session user"
export HOST="ubuntu"
export BUILD_SYSTEM="Ubuntu"

# USERNAME and HOSTNAME as specified above won't be honoured and will be set to
# flavour string acquired at boot time, unless you set FLAVOUR to any
# non-empty string.

export FLAVOUR="MyLiveCD"

Installing virtual box guest additions breaks startup

On boot, the casper scripts that configure the livecd environment creates an user with UID=999 (see /usr/share/initramfs-tools/scripts/casper-bottom/25adduser). If this UID is already used, the creation fails.

VirtualBoxGuestAdditions creates an user which may get the 999 UID

# This is the LSB version of useradd and should work on recent
# distributions
useradd -d /var/run/vboxadd -g 1 -r -s /bin/false vboxadd >/dev/null 2>&1
# And for the others, we choose a UID ourselves
useradd -d /var/run/vboxadd -g 1 -u 501 -o -s /bin/false vboxadd >/dev/null 2>&1

On my lubuntu it's the first command that creates the user vboxadd with an uid == 999.

So, I changed the uid for 501 with the command:

usermod -u 501 vboxadd

The English Ubuntu Wiki mentioned to pay attention to users with UID > 999, but did not include 999. And I removed the mention to UID > 999 as it has no reason to exist anymore.

Compiling VBoxGuestAdditions on a different architecture and kernel version

When compiling the vbox module, the system rely on the result of uname command. But, on a chrooted environment, the value return are the one of the host computer.

As the PATH is somehow manipulated during the execution, the easiest solution was to overwrite the regular /bin/uname with a script that basically does

/bin/uname.real $@ | sed "s/$KERNEL/$DEST_KERNEL/g; s/$PROCESSOR/$DEST_PROCESSOR/g"

The complete uname script can be found in the chroot_install_folder directory.

cladmi/lubuntu_live_cd