When user have enabled persistence, it could be nice to remember which extra packages they have installed.

We propose to use the term "your additional software" to mention to the user those packages in the GUI, notifications, etc.

This feature will be implemented in several steps.

Past research

Possible interfaces

1

Either in the greeter or upon login, an interface could appear offering the user to select which packages should be reinstalled (all unselected by default).

Having this choice in the greeter could allow users to install their preferred software without having an administrative password set.

This interface would quickly become messy, as soon as a desired additional package pulls dozens (if not hundreds) of dependencies.

2

Alternative idea: in tails-persistence-setup, allow selecting packages (among the ones additionally installed during the current session, and/or offer a "All installed additional packages" option) to be automatically re-installed next time. Then, at boot time, when persistence is enabled, our live-persistence script (or something else started from tails-greeter) would (unconditionally?) read this packages list from the persistent volume and install them.

Things to think about

security implications of this whole idea needs to be researched before diving in the code.

since the cached APT packages are hand picked by the user, security will depend on these packages and security of the persistent volume where the *.deb are going to be stored. Am I missing something here?

how to answer pontential apt/dpkg/debconf questions? record answers? force yes?
re-install these packages from cache only, or prefer fetching more up-to-date versions from online mirrors if available? If we want to fetch updates, when should the install start? Think about offline usage and about network fingerprint.
should the packages been installed before starting the session (required for packages related to session modification e.g. msva-perl) or after (e.g. requiring network, like firmware downloader)

Possible implementation tricks

Installing at startup, then upgrading

One solution to the upgrad/offline use problem might be to install the packages at from cache at startup, then to try to fetch upgrades and install them if network appears.

Creating a list of user-installed packages

A configuration snippet can be add in /etc/apt/apt.conf.d with a Dpkg::Post-Invoke option. This allows to trigger a script each time APT is run.

This script should query APT database and record all packages that are not in autoinstall state.

On boot time, that list should be filtered with packages that are already shipped with Tails.

Here's an example script which filters shipped packages on runtime instead:
comm -23 <(list-manually-installed-packages) <default-packages.txt >session-packages.txt
comm -23 <(cat session-packages.txt|sort) <(cat saved-packages.txt|sort) >> saved-packages.txt
It mantains a list of packages manually installed by the user in saved-packages.txt. This file should be placed in its own directory so it can be made persistent.

list-manually-installed-packages is another script which does what its name says. In squeeze it can be done with:
comm -3 <(dpkg -l | grep '^ii' | cut -d\  -f 3|sort) <(apt-mark showauto|sort)
When we move to wheezy it may simply become 'apt-mark showmanual', if it proves to be equivalent.

default-packages.txt is the list of packages shipped with Tails, generated at ISO creation time with list-manually-installed-packages

session-packages.txt is a temporary file, can be placed in /tmp