Quick ref.

Forces check on /dev/sda2 even if fs looks clean.
  sudo e2fsck -fvp /dev/sda2
-f   force
-v   verbose
-p   preen (ie try to fix fs)
fs must not be mounted.


e2fsck exit codes:
- 0  No errors
- 1  fs errors corrected
- 2  system should be rebooted
- 4  fs errors left uncorrected
- 8  operational error
- 16 usage or syntax error
- 32 fsck canceled by user request
- 128 shared library error