Developing live scripts and customisation hooks¶
vmdebootstrap is available in git and in Debian. The live image
processing requires several options which are only available in
versions of vmdebootstrap newer than version 0.5-2 available in
Debian Jessie. vmdebootstrap is able to run on Stretch, Jessie or
Wheezy and able to build any suite supported by debootstrap (and
and architecture supported by QEMU) on any of those versions of
Debian. This leads to a large matrix of build options and hooks.
Calls to vmdebootstrap are best scripted. See the README for notes on which options and settings are required to make a live image using vmdebootstrap.
The ‘common’ library contains functions and parameters which need to be used in all images, including:
export_env
mount_proc
disable_daemons
prepare_apt_source
replace_apt_source
remove_daemon_block
cleanup
cleanup¶
Ensure that proc is unmounted even if the customisation fails or else
the image build itself will fail to unmount $rootdir.
export_env¶
Debconf needs to be set in noninteractive mode to prevent the image build waiting for keyboard intervention.
mount_proc¶
Many packages require /proc to be mounted inside the chroot during
installation - cleanup must be specified as a trap if mount_proc is
used:
trap cleanup 0
disable_daemons¶
Packages which include a daemon must not start those daemons inside
the chroot as this will make the ${rootdir} appear busy and the unmount
will fail. All scripts need to use remove_daemon_block after package
installation is complete.
prepare_apt_source¶
The final Debian mirror location is not useful during the build when there is a faster mirror available during the build. This function moves the specified mirror file aside and uses the nearby mirror. Always use with replace_apt_source.
Ensure that the mirror and suite are passed as arguments to prepare_apt_source:
prepare_apt_source http://mirror/debian jessie
remove_daemon_block¶
After using disable_daemons, a policy script remains which needs
to be removed to allow daemons to start normally when the image itself
is booted. Use remove_daemon_block as the next step once package
installation is complete.
replace_apt_source¶
Requires prepare_apt_source to have been run first, then undoes the change to the apt sources and cleans up.
TASK_PACKAGES¶
Some task packages are useful to all images, these are specified here and should be included in the set of packages to be installed using all customisation scripts.
EXTRA_PACKAGES¶
Packages which are not part of an existing task but which are useful for all images and should be included in the set of packages to be installed using all customisation scripts.
New architectures¶
The precursor to new architecture support is vmdebootstrap support. A
default vmdebootstrap (with no customisation hook) will need to work
and any changes to the settings (e.g. --no-kernel --package linux-myarch-flavour)
There is default support for some architectures in vmdebootstrap
(e.g. armhf architectures select the armmp kernel), such support depends
on how many users would use the same kernel compared to the number of
possible kernel flavours for that architecture.
For a Debian LIVE image, all packages must exist in Debian.
The package list also needs a review - some packages will simply not exist for the specified architecture. Some architecture-specific packages need to be added, so each architecture has a particular customisation hook script. Package names frequently change between releases, so the package selection needs to be suite specific as well.