# Announcing session-migration now in ubuntu

Just fresh hot of the press, session-migration is now available in quantal.

This small tool is trying to solve a problem we encountered for a long time as a distributor, but had to postpone it way too long because of other priorities. :) It basically enables packagers and maintainers to migrate in user session data. Indeed, when you upgrade a package, the packaging tools are running under root permissions, and only hackish solutions was used in the past to enable us to change some parts of your user configuration[1], like adding the FUSA applet, adding new compiz plugins on the fly… There are tons of example when a distribution needs to migrate some user data (logged or not when the upgrade is proceeding) without patching heavily the upstream project to add a migration support there.

This tool is executed at session startup, in a sync fashion. It contains caching and tries to execute the minimal chunk[2], based on the design of the excellent gconf->gsettings migration tool. It contains as well a dh-migrations package, with a debhelper hook (--with migrations calling dh_migrations), so that client desktop packages just have to ship a debian/<package>.migrations file linking to their migration scripts which will be shipped in the right directory. We can even imagine in the near future that when you install such a package, you end up with a notification that a session restart is necessary (and not a full reboot). Note as well that the migration happens per user and per session, so it's really important that the scripts are idempotents.

Was 3 days of fun coding this. ;) All of the C and perl codes are covered by a short, but complete testsuite run during the package build, so no breakage hopefully. ;) Associated man pages are session-migration and dh_migrations.

You can find more details on the launchpad specification as well as the recorded streamed discussion from UDS (part 1, part 2).

The illustrated session icon is under a GPL licence, found on iconfinder.

#### Notes

[1] Knowing that we try to respect as more as possible the gold rule and always trying to only change default, which is not possible sometimes

[2] but support multiples layers based on XDG_DATA_DIRS