Description:

livefsedit 0.0.4

A tool to "edit" Ubuntu live server CDs
There are a few reasons the Ubuntu live server ISOs as shipped may not
quite be what you want. Here are some examples:


You want to make an ISO that does a completely automated install


You want packages that are not in the package repository by default
to be available during install, even when there is no network (or
only a very isolated network).


You want to add an argument to the default kernel command line.


You want to inject a new version of the subiquity snap for testing.


This script aims to help you making modified versions of the
distributed ISOs with changes such as those above.
Some of the things it does probably work on desktop installer ISOs too
but I haven't thought very hard about that side of things yet.
Dependencies
This script is pretty Linux-dependent and requires xorriso and
mksquashfs to be available on $PATH. Some actions require the
python3-debian package to be installed and gpg command to be
available.
It needs to be run as root (although possibly using FUSE variants for
all the mounts would allow it to run as a regular user, maybe).
General invocation
The basic idea behind this tool is that you tell it where to find the
source ISO, where to put the modified ISO and a list of actions that
make up the modifications. So an invocation always looks somewhat like
this:
# livefs-edit $source.iso $dest.iso [actions]

Actions can be specified two ways: on the command line or in a YAML
file. Each action has a name and many of them take arguments.
On the command line, actions and arguments are specified like:
--action-name arg1 arg2 --next-action-name

Arguments that are interpreted as boolean interpret 'on', 'yes',
'true' (case insensitively) as true.
Alternatively (if shell quoting starts to get painful), the actions
can be passed as a YAML file, using the --action-yaml flag:
# livefs-edit $source.iso $dest.iso --action-yaml examples/example.yaml

The YAML file should be a list of mappings. Each mapping names the
actions with name and lists any arguments by name, for example:
- name: add-cmdline-arg
arg: autoinstall
persist: false
- name: shell
- name: add-packages-to-pool
packages:
- casper
- valgrind

Directory structure
This script does all its work in a temporary directory. Within that
directory the original ISO is mounted at old/iso and what will be
packed into the new ISO is present at new/iso (the script uses a lot
of overlayfs mounts to avoid copying large amounts of data around,
and also only repack things when there are changes).
Many actions require a writable emulation of the root filesystem that
the installer will run in. By default this is created at rootfs in
the main temporary directory, but this can be customized.
In general, things from the original ISO are mounted in old/ and are
either read-only or should be treated as such. Writable versions for
the new ISO live in new/ (mostly).
Actions
setup-rootfs
argument: target (default: "rootfs")
This action sets up a writable emulation of the root filesystem that
the installer will run in at the directory named by target. Changes
to this rootfs will be present in the rootfs used by installer on the
modified ISO.
Many actions will do this implicitly but it may be clearer to be
explicit about the target directory name if later shell or cp
actions refer to paths in the rootfs.
shell
argument: command (default: null)
Runs a shell (bash) in the main temporary directory. If command is
present, this is the command that is run. If not, an interactive shell
is run. If the shell (command or interactive) exits with a non-zero
code, that aborts the run.
cp
argument: source
argument: dest
Copy a file. If source or dest are relative they are assumed to be
relative to the main temporary directory. So something like this:
--cp /my/custom/initrd new/iso/casper/initrd

to replace the initrd.
inject-snap
argument: snap
argument: channel (default: "stable")
Inject the passed snap into the rootfs the installer runs in. This is
used to test new versions of subiquity. If there is an assert
alongside the snap, this will be copied into the ISO too and the snap
set up to track the passed channel, otherwise it is installed
unasserted.
add-snap-from-store
argument: snap_name
argument: channel (default: "stable")
A wrapper around `--inject-snap`` that downloads the specified snap
from the store first.
edit-squashfs
argument: name
argument: add_sys_mounts (default: true)
Mount the squashfs named name at new/{name} and arrange for it be
repacked if there are any changes before the new ISO is made.
add_sys_mounts controls whether the usual chroot setup stuff is done
(mounting /dev, /proc/ etc, setting up /etc/resolv.conf).
add-cmdline-arg
argument: arg
argument: persist (default: true)
Add an argument to the default kernel command line. If persist is
true, it will be present on the default kernel command line of the
installed system as well.
add-autoinstall-config
argument: autoinstall_config
Add the provided autoinstall config to the ISO so it is used by
default. This also adds "autoinstall" to the default kernel command
line.
autoinstall_config is the path to a YAML file which can contain
either the autoinstall config directly or a cloud-init user-data file
(in which case it can contain other configuration for the live
installer session, such as ssh keys to be used for the installer
user).
add-debs-to-pool
argument: list of deb files
Add the passed deb files to the repository on the CD so that they are
available for installation while the installer is running, even if the
install is done offline.
This will generate a new Ed25519 GPG key, sign the package repository
on the ISO with it, arrange for the public part to end up in
/etc/apt/trusted.gpg.d/custom-iso-key.gpg in the installed system,
and then throw the private part away. You should be aware of this
change to the default apt configuration! Deleting this file in an
autoinstall late-command would be a reasonable thing to do, unless
you want the option of using the ISO as an apt repository later on.
add-packages-to-pool
argument: list of package names
This is a wrapper around add-debs-to-pool which takes package names
rather than deb files. It downloads the listed packages and any others
needed to satisfy their dependencies from the main Ubuntu archive and
passes them to add-debs-to-pool. Do read the note about GPG in the
description of that action.
unpack-initrd
argument: target (default: "new/initrd")
Unpack the initrd using unmkinitramfs into target (contents will
likely end up in subdirectories called things like early, early2
and main, at least on amd64) and arrange for these to be repacked
into a replacement initrd for the modified ISO if any changes are made.

License

For personal and professional use. You cannot resell or redistribute these repositories in their original state.

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