fstab - static information about the filesystems
The file fstab contains descriptive information about the filesystems the system can mount. fstab is only read by programs, and not written; it is the duty of the system administrator to properly create and maintain this file. The order of records in fstab is important because fsck(8), mount(8), and umount(8) sequentially iterate through fstab doing their thing.
Each filesystem is described on a separate line. Fields on each line are separated by tabs or spaces. Lines starting with '#' are comments. Blank lines are ignored.
The following is a typical example of an fstab entry:
The first field (fs_spec).
For ordinary mounts, it will hold (a link to) a block special device node (as created by mknod(2)) for the device to be mounted, like `/dev/cdrom' or `/dev/sdb7'. For NFS mounts, this field is <host>:<dir>, e.g., `knuth.aeb.nl:/'. For filesystems with no storage, any string can be used, and will show up in df(1) output, for example. Typical usage is `proc' for procfs; `mem', `none', or `tmpfs' for tmpfs. Other special filesystems, like udev and sysfs, are typically not listed in fstab.
LABEL=<label> or UUID=<uuid> may be given instead of a device name. This is the recommended method, as device names are often a coincidence of hardware detection order, and can change when other disks are added or removed. For example, `LABEL=Boot' or `UUID=3e6be9de-8139-11d1-9106-a43f08d823a6'. (Use a filesystem-specific tool like e2label(8), xfs_admin(8), or fatlabel(8) to set LABELs on filesystems).
It's also possible to use PARTUUID= and PARTLABEL=. These partitions identifiers are supported for example for GUID Partition Table (GPT).
Note that mount(8) uses UUIDs as strings. The string representation of the UUID should be based on lower case characters.
The second field (fs_file).
The third field (fs_vfstype).
An entry swap denotes a file or partition to be used for swapping, cf. swapon(8). An entry none is useful for bind or move mounts.
More than one type may be specified in a comma-separated list.
mount(8) and umount(8) support filesystem subtypes. The subtype is defined by '.subtype' suffix. For example 'fuse.sshfs'. It's recommended to use subtype notation rather than add any prefix to the first fstab field (for example 'sshfs#example.com' is deprecated).
The fourth field (fs_mntops).
It is formatted as a comma-separated list of options. It contains at least the type of mount (ro or rw), plus any additional options appropriate to the filesystem type (including performance-tuning options). For details, see mount(8) or swapon(8).
Basic filesystem-independent options are:
- use default options: rw, suid, dev, exec, auto, nouser, and async.
- do not mount when "mount -a" is given (e.g., at boot time)
- allow a user to mount
- allow device owner to mount
- or x-<name> for use by fstab-maintaining programs
- do not report errors for this device if it does not exist.
The fifth field (fs_freq).
The sixth field (fs_passno).
The proper way to read records from fstab is to use the routines getmntent(3) or libmount.
The keyword ignore as a filesystem type (3rd field) is no longer supported by the pure libmount based mount utility (since util-linux v2.22).
The ancestor of this fstab file format appeared in 4.0BSD.
This man page is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.