Repairing FFS / UFS filesystem on OpenBSD

In most cases, when the filesystem is corrupted, it's automatically fixed before booting. In some other cases, the system won't be able to boot properly and will start in single user mode. A message similar to the following will be displayed.

THE FOLLOWING FILE SYSTEM HAD AN UNEXPECTED INCONSISTENCY
ffs: a19c626adc5e60ef .l (/home)
Automatic file system check failed; help!
Enter the pathname of the shell or press [Enter] for sh:

Note the value after ffs:, it will help to identify which disk is concerned. Then, press [Enter].

By default, the keyboard is set to en_US / qwerty, it can be changed with the kbd command.

# kbd fr
kbd: keyboard mapping set to fr

To identify the partition reported in the error message, it's possible to use disklabel. From the error above we know that the error comes from the partition l (lowercase L) on disk with uid a19c626adc5e60ef, mounted as /​home, we have to find which disk is concerned.

# disklabel sd2
/dev/rsd2c:
[...]
duid: a19c626adc5e60ef
[...]
#           size           offset  fstype [fsize bsize   cpg]
[...]
l:          xxxxxxxx         xxxxxx  4.2BSD   4096 1298 1062 # /home

The partition is sd2l.

The filesystem can be repaired using the fsck_ffs command.

# fsck_ffs /dev/sd2l

fsck will list the problems and ask if it should try to fix them, one by one. Type y to validate the current one, or F to autocorrect all of them. Be aware that automatic validation could create problems in some situations.

• Wikipedia: Unix File System
• Why OpenBSD rocks: FFS2
• OpenBSD manual: fsck_ffs
• OpenBSD manual: kbd
• OpenBSD manual: disklabel