The file
fstab contains descriptive information about the various file systems.
It is the duty of the system administrator to properly create and maintain this file.
fstab can be modified by special utils (e.g.
fstab-sync (8)). Each filesystem is described on a separate line; fields on each line are separated by tabs
or spaces. Lines starting with '#' are comments. The order of records in
fstab is important because
fsck(8) ,mount(8) , and
umount(8) sequentially iterate through
fstab doing their thing.
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 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 ), 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.
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 options have a look at
nfs(5) . Common for all types of file system are the options ``noauto''
(do not mount when "mount -a" is given, e.g., at boot time), ``user''
(allow a user to mount), ``owner''
(allow device owner to mount), ``pamconsole'' (allow a user at the console to mount), and ``comment''
(e.g., for use by fstab-maintaining programs).
The ``owner'', ``pamconsole'' and ``comment'' options are Linux-specific.
For more details, see
mount(8) .
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 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) .