Ubuntu Manpages

fstab

static information about the filesystems

/etc/fstab

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 comments, blank lines are ignored. 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).

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 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.

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).

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 (fs_vfstype).

This field 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.

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 depreacated).

The fourth field (fs_mntops).

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 mount(8). For documentation on the available swap options, see swapon(8).

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 mountall(8) program that mounts filesystem during boot also recognises additional options that the ordinary mount(8) tool does not. These are: ``bootwait'' which can be applied to remote filesystems mounted outside of /usr or /var, without which mountall(8) would not hold up the boot for these; ``nobootwait'' which can be applied to non-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).

This field 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).

This field is used by the fsck(8) program to determine 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 be checked.

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

/etc/fstab, <fstab.h>

mount(8), mountall(8), swapon(8), fs(5), nfs(5), xfs(5), proc(5), getmntent(3)

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 ftp://ftp.kernel.org/pub/linux/utils/util-linux/.