NAME [Toc] [Back]
fstab - static information about the file systems
SYNOPSIS [Toc] [Back]
DESCRIPTION [Toc] [Back]
fstab is an ASCII file that resides in directory /etc. Programs read
it, but do not write to or from it. System administrators are
responsible for creating and maintaining this file properly.
/etc/fstab contains a list of mountable file-system entries. Each
file-system entry appears on a separate line, and consists of fields
separated by one or more blanks or tabs.
The order of entries in /etc/fstab is important only for entries
without a pass number field. Entries without a pass number are
sequentially checked by fsck (see fsck(1M)) after the entries with a
pass number have been checked.
Each file-system entry must contain a device special file and may
additionally contain all of the following fields, in the following
pass number (on parallel fsck)
If any field after the name of the device special file is present, all
fields must be present in the order indicated, to ensure correct
Entries from this file are accessed using getmntent() (see
The fields are separated by white space, and a # as the first nonwhitespace
character in an entry or field indicates a comment.
device special file A block device special file name. This field is
used by fsck, mount, swapon, crashconf, and other
commands to identify the location of the storage
device on which the file system resides.
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directory Name of the root of the mounted file system that
corresponds to the device special file. If type
is swapfs, directory can be the name of any
directory within a file system. Only one
directory should be specified per file system.
directory must already exist and must be given as
an absolute path name.
type Can be swap, swapfs, dump, ignore, or a file
system type (for example, hfs, vxfs, cdfs, nfs, or
If type is swap, the device special file is made
available as an area of swap space by the swapon
command (see swapon(1M)). The options field is
valid. The fields directory, pass number, and
backup frequency are ignored for swap entries.
If type is swapfs, the file system in which
directory resides is made available as swap space
by swapon. The options field is valid. The
fields device special file, pass number, and
backup frequency are ignored for swapfs entries.
If type is dump, the device special file is made
available as an area into which a system crash
dump may occur, by the crashconf command (see
crashconf(1M)). The fields options, directory,
pass number, and backup frequency are ignored for
Entries marked by the type ignore are ignored by
all commands and can be used to mark unused
sections. If type is specified as either ignore,
dump, swap, or swapfs, the entry is ignored by the
mount and fsck commands (see mount(1M) and
fsck(1M)). fsck also ignores entries with type
specified as cdfs, nfs, or lofs.
options A comma-separated list of option keywords, as
found in mount(1M) or swapon(1M). The keywords
used depend on the parameter specified in type.
backup frequency Reserved for possible use by future backup
pass number Used by the fsck command to determine the order in
which file system checks are done. The root file
system should be specified with a pass number of
1, to be checked first, and other file systems
should have larger numbers. (A file system with a
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pass number of zero is ignored by the fsck
File systems within a drive should be assigned
different pass numbers, but file systems on
different drives can be checked on the same pass,
to utilize possible parallelism available in the
hardware. If pass number is not present, fsck
checks each such file system sequentially after
all eligible file systems with pass numbers have
comment An optional field that begins with a # character
and ends with a new-line character. Space from
the pass number to the comment field (if present)
or to the new-line is reserved for future use.
There is no limit to the number of device special file fields in
NETWORKING FEATURES [Toc] [Back]
If the field type is nfs, a remote NFS file system is implied. For
NFS file systems, the device special file should be the serving
machine name followed by ":" followed by the path on the serving
machine of the directory being served. The pass number and backup
frequency fields are ignored for NFS entries.
EXAMPLES [Toc] [Back]
Examples of typical /etc/fstab entries:
Add an HFS file system at /home using default mount options;
(backup frequency 0) fsck pass 2:
/dev/dsk/c0t6d0 /home hfs defaults 0 2 # /home disk
Add a swap device to a system managed using LVM, with default
options (Note, the directory field (/) cannot be empty, even
though it is ignored):
/dev/vg01/lv10 / swap defaults 0 0 # swap device
Add a swap device on a system implementing whole-disk layout to
use the space after the end of the file system (options=end):
/dev/dsk/c0t5d0 / swap end 0 0 # swap at end of device
Add file system swap space on the file system containing
directory /swap. type is swapfs; set options to min=10,
lim=4500, res=100, and pri=0 (see swapon(1M)) for explanation of
options). device field is ignored but must not be empty:
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default /swap swapfs min=10,lim=4500,res=100,pri=0 0 0
(Note that both a file system entry and a swap entry are required
for devices providing both services.)
Use a device for dump space if the system crashes. directory
field is ignored but must not be empty:
/dev/dsk/c0t5d0 / dump defaults 0 0
(Note that both a swap entry and a dump entry are required for
devices providing both services.)
DEPENDENCIES [Toc] [Back]
Here is an example for mounting an NFS file system for systems that
support NFS file systems:
server:/mnt /mnt nfs rw,hard 0 0 #mount from server.
AUTHOR [Toc] [Back]
fstab was developed by HP, AT&T, Sun Microsystems, Inc., and the
University of California, Berkeley.
FILES [Toc] [Back]
SEE ALSO [Toc] [Back]
fsck(1M), mount(1M), swapon(1M), crashconf(1M), getfsent(3X),
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