Section: File Formats (5)
Updated: August 2010Index
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fstab - static information about the filesystems
contains descriptive information about the various file systems.
is only read by programs, and not written; it is the duty of the system
administrator to properly create and maintain this file. 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
order of records in
is important because
sequentially iterate through
doing their thing.
The first field
This field describes the block special device or
remote filesystem to be mounted.
For ordinary mounts it will hold (a link to) a block special
device node (as created by
for the device to be mounted, like `/dev/cdrom' or `/dev/sdb7'.
For NFS mounts one will have <host>:<dir>, e.g., `knuth.aeb.nl:/'.
For procfs, use `proc'.
Instead of giving the device explicitly, one may indicate
the filesystem that is to be mounted by its UUID or
writing LABEL=<label> or UUID=<uuid>,
e.g., `LABEL=Boot' or `UUID=3e6be9de-8139-11d1-9106-a43f08d823a6'.
It's also possible to use PARTUUID= and PARTLABEL=. These partitions identifiers
are supported for example for GUID Partition Table (GPT).
for more details about devices identifiers.
uses UUIDs as strings. The string representation of the UUID should be based on
lower case characters.
The second field
This field describes the mount point for the filesystem. For swap partitions, this
field should be specified as `none'. If the name of the mount point
contains spaces these can be escaped as `\040'.
The third field
This field describes the type of the filesystem. Linux supports lots
of filesystem types, such as
and possibly others. For more details, see
For the filesystems currently supported by the running kernel, see
denotes a file or partition to be used
for swapping, cf.
is useful for bind or move mounts.
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
The fourth field
This field describes the mount options associated with the filesystem.
It is formatted as a comma separated list of options. It contains at least
the type of mount plus any additional options appropriate to the filesystem
type. For documentation on the available mount options, see
For documentation on the available swap options, see
Basic file system 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
for use by fstab-maintaining programs
do not report errors for this device if it does not exist.
The fifth field
This field is used for these filesystems by the
command to determine which filesystems need to be dumped. If the fifth
field is not present, a value of zero is returned and
will assume that the filesystem does not need to be dumped.
The sixth field
This field is used by the
program to determine the order in which filesystem checks are done at
reboot time. The root filesystem should be specified with a
of 1, and other filesystems should have a
of 2. Filesystems within a drive will be checked sequentially, but
filesystems on different drives will be checked at the same time to utilize
parallelism available in the hardware. If the sixth field is not present
or zero, a value of zero is returned and
will assume that the filesystem does not need to be checked.
The proper way to read records from
is to use the routines
as filesystem type (3rd field) is not more supported by the pure
libmount based mount utility (since util-linux v2.22).
The ancestor of this
file format appeared in 4.0BSD.
This man page is part of the util-linux package and is available from
- SEE ALSO