path: root/sys-utils/fstab.5

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.\"     @(#)fstab.5	6.5 (Berkeley) 5/10/91
.\"
.\" Modified Sat Mar  6 20:45:03 1993, faith@cs.unc.edu, for Linux
.\" Sat Oct  9 10:07:10 1993: converted to man format by faith@cs.unc.edu
.\" Sat Nov 20 20:47:38 1993: hpfs documentation added
.\" Sat Nov 27 20:23:32 1993: Updated authorship information
.\" Wed Jul 26 00:00:00 1995: Updated some nfs stuff, joey@infodrom.north.de
.\" Tue Apr  2 00:38:28 1996: added info about "noauto", "user", etc.
.\" Tue Jun 15 20:02:18 1999: added LABEL and UUID
.\" Sat Jul 14 2001: Michael K. Johnson <johnsonm@redhat.com> added -O
.\"
.TH FSTAB 5 "August 2010" "util-linux" "File Formats"
.SH NAME
fstab \- static information about the filesystems
.SH SYNOPSIS
.B /etc/fstab
.SH DESCRIPTION
The file
.B fstab
contains descriptive information about the various file systems.
.B fstab
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
.B fstab
is important because
.BR fsck (8),
.BR mount (8),
and
.BR umount (8)
sequentially iterate through
.B fstab
doing their thing.

.B The first field
.RI ( fs_spec ).
.RS
This field describes the block special device or
remote filesystem to be mounted.
.LP
For ordinary mounts it will hold (a link to) a block special
device node (as created by
.BR mknod (8))
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'.
.LP
Instead of giving the device explicitly, one may indicate
the filesystem that is to be mounted by its UUID or
LABEL (cf.
.BR e2label (8)
or
.BR xfs_admin (8)),
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).

See
.BR mount (8),
.BR blkid (8)
or
.BR lsblk (8)
for more details about devices identifiers.

.LP
Note that
.BR mount (8)
uses UUIDs as strings. The string representation of the UUID should be based on
lower case characters.
.RE

.B The second field
.RI ( fs_file ).
.RS
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'.
.RE

.B The third field
.RI ( fs_vfstype ).
.RS
This field describes the type of the filesystem.  Linux supports lots
of filesystem types, such as
.IR adfs ,
.IR affs ,
.IR autofs ,
.IR coda ,
.IR coherent ,
.IR cramfs ,
.IR devpts ,
.IR efs ,
.IR ext2 ,
.IR ext3 ,
.IR hfs ,
.IR hpfs ,
.IR iso9660 ,
.IR jfs ,
.IR minix ,
.IR msdos ,
.IR ncpfs ,
.IR nfs ,
.IR ntfs ,
.IR proc ,
.IR qnx4 ,
.IR reiserfs ,
.IR romfs ,
.IR smbfs ,
.IR sysv ,
.IR tmpfs ,
.IR udf ,
.IR ufs ,
.IR umsdos ,
.IR vfat ,
.IR xenix ,
.IR xfs ,
and possibly others. For more details, see
.BR mount (8).

For the filesystems currently supported by the running kernel, see
.IR /proc/filesystems .

An entry
.I swap
denotes a file or partition to be used
for swapping, cf.\&
.BR swapon (8).
An entry
.I none
is useful for bind or move mounts.

.BR mount (8)
and
.BR umount (8)
support filesystem
.IR 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).
.RE

.B The fourth field
.RI ( fs_mntops ).
.RS
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
.BR mount (8).
For documentation on the available swap options, see
.BR swapon (8).

Basic file system independent options are:
.TP
.B defaults
use default options: rw, suid, dev, exec, auto, nouser, and async.
.TP
.B noauto
do not mount when "mount -a" is given (e.g., at boot time)
.TP
.B user
allow a user to mount
.TP
.B owner
allow device owner to mount
.TP
.B comment
or
.B x-<name>
for use by fstab-maintaining programs
.TP
.B nofail
do not report errors for this device if it does not exist.
.RE

.B The fifth field
.RI ( fs_freq ).
.RS
This field is used for these filesystems by the
.BR dump (8)
command to determine which filesystems need to be dumped.  If the fifth
field is not present, a value of zero is returned and
.B dump
will assume that the filesystem does not need to be dumped.
.RE

.B The sixth field
.RI ( fs_passno ).
.RS
This field is used by the
.BR fsck (8)
program to determine the order in which filesystem checks are done at
reboot time.  The root filesystem should be specified with a
.I fs_passno
of 1, and other filesystems should have a
.I fs_passno
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
.B fsck
will assume that the filesystem does not need to be checked.
.RE

.SH NOTES
The proper way to read records from
.B fstab
is to use the routines
.BR getmntent (3)
or
.BR libmount .

The keyword
.B ignore
as filesystem type (3rd field) is not more supported by the pure
libmount based mount utility (since util-linux v2.22).

.SH FILES
.IR /etc/fstab ,
.I <fstab.h>
.SH "SEE ALSO"
.BR findmnt (8),
.BR mount (8),
.BR swapon (8),
.BR fs (5),
.BR getmntent (3)
.SH HISTORY
The ancestor of this
.B fstab
file format appeared in 4.0BSD.
.\" But without comment convention, and options and vfs_type.
.\" Instead there was a type rw/ro/rq/sw/xx, where xx is the present 'ignore'.
.SH AVAILABILITY
This man page is part of the util-linux package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.