The file fstab contains descriptive information about the various file
systems. 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 com-
ments. The order of records in fstab is important because fsck(8),
mount(8), and umount(8) sequentially iterate through fstab doing their
thing, though at boot time mountall(8) may process the file out-of-
order when it believes it is safe to do so.
The first field, (fs_spec), 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 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'.
Instead of giving the device explicitly, one may indicate the (ext2 or
xfs) filesystem that is to be mounted by its UUID or volume label (cf.
e2label(8) or xfs_admin(8)), writing LABEL=<label> or UUID=<uuid>,
e.g., `LABEL=Boot' or `UUID=3e6be9de-8139-11d1-9106-a43f08d823a6'.
This will make the system more robust: adding or removing a SCSI disk
changes the disk device name but not the filesystem volume label.
The second field, (fs_file), describes the mount point for the filesys-
tem. For swap partitions, this field should be specified as `none'. If
the name of the mount point contains spaces these can be escaped as
The third field, (fs_vfstype), describes the type of the filesystem.
Linux supports lots of filesystem types, such as adfs, affs, autofs,
coda, coherent, cramfs, devpts, efs, ext2, ext3, hfs, hpfs, iso9660,
jfs, minix, msdos, ncpfs, nfs, ntfs, proc, qnx4, reiserfs, romfs,
smbfs, sysv, tmpfs, udf, ufs, umsdos, vfat, xenix, xfs, and possibly
others. For more details, see mount(8). For the filesystems currently
supported by the running kernel, see /proc/filesystems. An entry swap
denotes a file or partition to be used for swapping, cf. swapon(8). An
entry ignore causes the line to be ignored. This is useful to show
disk partitions which are currently unused. An entry none is useful
for bind or move mounts.
The fourth field, (fs_mntops), 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 options for non-
nfs file systems, see mount(8). For documentation on all nfs-specific
remote filesystems to explicitly instruct mountall(8) not to hold up
the boot for them; ``optional'' which causes the entry to be ignored if
the filesystem type is not known at boot time; and ``showthrough''
which permits a mountpoint to be mounted before its parent mountpoint
(this latter should be used carefully, as it can cause boot hangs).
The fifth field, (fs_freq), is used for these filesystems by the
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 dump
will assume that the filesystem does not need to be dumped.
The sixth field, (fs_passno), is used by the fsck(8) program to deter-
mine the order in which filesystem checks are done at reboot time. The
root filesystem should be specified with a fs_passno of 1, and other
filesystems should have a 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 fsck will assume that the filesystem does not need to
The proper way to read records from fstab is to use the routines getmn-
getmntent(3), mount(8), mountall(8), swapon(8), fs(5), nfs(5)
The ancestor of this fstab file format appeared in 4.0BSD.
This man page is part of the util-linux-ng package and is available
Linux 2.2 15 June 1999 FSTAB(5)
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