The fsck program checks UFS file systems and performs corrections
to grant disk integrity. fsck can correct inconsistencies such as
unreferenced inodes, missing blocks in the free list, or incorrect counts in
the superblock.
File system corruption is caused by improper shutdown, hardware and power supply failures, unproper physically write protect of a mounted file system, a mounted file system going off line, or missing synchronization before shutdown.
fsck is run at boot noninteractively, making any safe corrections. If an
unexpected inconsistency is detected, fsck exits leaving the system in
single-user mode, and asking manual rerun, which allows yes or no anwser
to fsck prompts. fsck syntax is:
/usr/sbin/fsck[options ...] [file_system ...]
If a file system is not specified, all the file systems in /etc/fstab
are checked. File systems must be specified as raw devices.
N.B. The root file system must be checked in single-user
mode and must be mounted read only. To go to single-user mode, use the
shutdown command.
Note that fsck is used only for UFS. AdvFS uses
write-ahead logging instead and the recovery log for inconsistencies and
corrections at mount.
If a UFS file system mount operation fails with a FATAL ERROR
message and fsck cannot recover damaged i-nodes and file
lost+found is missing or unusable, the system will boot in single user.
To restart the system do:
# mount -a # cd /etc # ed fstab .... comment out problem disk # reboot