message = Recommended for advanced users ONLY.}}

Filesystems are corrupted, due to a power failure or system crash. Generally, after a system crash or power outage (what? No UPS?), the system will come up and repair itself. If you are using a journalling filesystem like ext3fs, jfs, xfs or resiserfs, it will usually perform a roll-forward recovery from its journal file and carry on. Even with the older ext2fs, the system usually runs an fsck (file system check) on the various file systems and repairs them automatically. However, just occasionally manual intervention is required - ; you might have to answer 'Y' to a string of questions (answering 'N' will get you nowhere unless you intend to perform really low-level repairs yourself in a last-ditch attempt to avoid data loss). In the worst case, you might have to reboot from rescue media and manuall run the e2fsck (or similar) command against each filesystem in turn. For example:

* If the program complains that the superblock - the master block that links to everything else - is corrupted, it is useful to remember that the superblock is so critical that it is duplicated every 8192 blocks through the filesystem and you can tell e2fsck to use one of the backups:

* One or more filesystems cannot be found and mounted: Check the contents of /etc/fstab - in making quick alterations here, typographical errors are common. You can use the e2label command to view the label of each filesystem: some distributions set these to the mount point so you can figure out what is what.