What annual or quarterly maintenance do you do on your Linux Servers?

quarterly reboot [ usually with kernel upgrade ], checking if startup scripts ware not messed up and all required services get up properly.

HA / failover testing - take master down, check if slave kicks in, then the other way around.

You do not want to do your backups quarterly. That should be done daily, or at most, weekly. If things break down, you will lose 3 months of work otherwise.

• Check filesystem usage (looking at trends via ORCA or similar graphs) for things like out-of-control logs, etc.
  - Defragment XFS filesystems (xfs_fsr).
  - On multiuser systems, I'll kill stale sessions and leftover processes.
  - Clean out tmp directories, etc.

Nothing. All scheduled maintenance is done monthly at the most, if not weekly or daily. We are in the server room often enough that they get dusted and cleaned more often than yearly or quarterly anyways.