The fsck command [1] is often used as a euphemism for a well-known swear word – and not just because it is a four-letter word that starts with f and ends with k. Typically, the command becomes relevant only when a filesystem needs repairing before the computer will finish booting or starting a graphical interface, and the repair work requires human intervention. In such circumstances, users may feel like swearing as they try to cope with their limited knowledge of the command. However, with more knowledge of fsck's background and options, such moments become much less alarming.

An abbreviation of FileSystem Consistency Check, fsck is installed by default on Linux systems as part of the util-linux package. Properly speaking, it is not a separate command at all, but a front end for filesystem-checking commands such as e2fsck, dosfsck, and fsckvfat, all of which work in very similar ways, usually in close association with /etc/fstab [2], which lists the available filesystems. These commands can still be run separately, but, thanks to fsck, users no longer need to remember each of them. Instead, in most cases fsck calls the appropriate command as needed, and the individual commands are only needed in advanced circumstances that few users are likely to encounter.

For convenience, either run fdisk -l (Figure 1) or else run less /etc/fstab before using fsck (Figure 2). Either command gives you a list of partitions on the systems, which can help you ensure that you make all necessary repairs. Make sure you run fsck on the correct drive. Finding the correct drive is essential, because it is possible to bypass fsck's defaults and run on a mounted drive, which can permanently corrupt the drive. Instead, use umount [3] to unmount the filesystem first. Should the filesystem not be unmountable – as often happens with the root partition at boot time – start a Live DVD such as GParted to run fsck.

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