Fsck

From iA wiki

Acronym: File System Check

A utility found on unix-like ooperating systems such as linux that check file system structures for errors. It is normally run at boot if the machine is turned off without a drive being unmounted and when a drive has not been checked after a certain number of boots.

Journaling filesystems such as reiserFS avoid the long delay that can be caused while a large drive contain a lot of files is fscked.