Common problems of configuration files and shared homedirs
A common problem on system with shared homedirs (shared e.g. via nfs or shared by multiple version of ubuntu on the system, e.g. one test install for the current development release and one of the stable release) is that sometimes configuration files change in a not backward compatible way. This causes problems if e.g. one system runs a older version of the application then the other. It also prevents downgrades and rollbacks from working properly. Note that this is not limited to /home, the same problem applies to /etc and package downgrades.
Some guidelines for configuration files:
- when the configuration changes in a backward incompatible way it should get a new name
- when the old configuration is read, the app should convert it to the new format but write it out under the new name
This will ensure that shared homedirs work and also that tools like apt-btrfs-snapshot will be able to rollback packages without unexpected breakage.