When Linux starts, it automatically mounts the file systems
specified in the file
/etc/fstab. By revising
this file, you can customize the operation of your system.
When you install Linux, the installation program configures the
file
/etc/fstab to specify what filesystems are
to be mounted when the system is started. Here's a typical
/etc/fstab file:
# /etc/fstab: static file system information.
#
# <file system> <mount point> <type> <options> <dump> <pass>
/dev/hda2 / ext2 defaults 0 1
/dev/hda3 none swap sw 0 0
proc /proc proc defaults 0 0
The first three lines, those beginning with a hash mark (#), are
comments that are ignored by the system; they merely help human
readers identify and understand the file. The next three lines each
specify a filesystem to be mounted at system startup. Six columns of
information appear:
-
Filesystem
-
The device that contains the
filesystem.
-
Mount point
-
The system directory that will hold the
filesystem.
-
Filesystem type
-
Specifies the type of the
filesystem. Popular types include:
-
ext2
-
the standard Linux filesystem
-
swap
-
the standard Linux swap filesystem
-
proc
-
a special filesystem provided by the kernel, used by system
components to obtain system information in a standard way
-
iso9660
-
the standard filesystem used on CD-ROM
-
msdos
-
the standard MS-DOS filesystem
See the man page for
mount for other filesystem types.
-
Mount options
-
Specifies the options given when the
filesystem is mounted. If multiple options are given, each is
separated from the next by a comma (,); no spaces appear within the
list of options. Popular options include:
-
defaults
-
Specifies a series of options appropriate for most
filesystems. For details, see the man page for
mount.
-
errors=remount-ro
-
Specifies that if errors are found when the filesystem is
checked, the filesystem will be remounted in read-only mode so that
the system administrator can analyze the errors without risking
further damage.
-
sw
-
Specifies that the filesystem will be mounted as a swap
partition.
-
ro
-
Specifies that the filesystem will be mounted for read access
only. This option is always specified for CD-ROM devices and may be
specified for other devices.
-
noauto
-
Specifies that the filesystem will not be automatically mounted
at system startup.
In addition, the
user option can be specified. This option allows
any user - not only
root - to mount the
filesystem.
-
Dump flag
-
Specifies whether the
dump command will create a backup of the
filesystem. Filesystems with no value or a value of zero will not be
dumped.
-
Pass
-
Specifies the order in which filesystems
are checked at boot time. No value or a value of zero specifies that
the filesystem will not be checked.
You can modify the lines within the
/etc/fstab file and add new lines as you see
fit. For example, here's a line that specifies a CD-ROM drive:
/dev/cdrom /cdrom iso9660 ro
By adding this file to the
/etc/fstab file,
you instruct the system to mount the CD-ROM filesystem when the system
starts. If you don't want the filesystem automatically mounted, you
can specify this line:
/dev/cdrom /cdrom iso9660 ro,noauto
The system will not automatically mount the CD-ROM filesystem
described by this line, but you can mount the CD-ROM by using the
mount command. Because the system already knows the
device, mount point, filesystem type, and options, you can abbreviate
the mount command to:
mount /cdrom
or:
mount /dev/cdrom
Either of these is equivalent to:
mount -t iso9660 -o ro /dev/cdrom /cdrom
You can automatically mount additional hard disk partitions by
describing them in the
/etc/fstab
file:
/dev/hdb1 /home ext2 defaults
Another tip is to use an entry in the
/etc/fstab file to allow users other than
root to mount a floppy disk:
/dev/fd0 /floppy auto noauto,user
Just as you can use the
mount and
unmount commands to explicitly mount and unmount
filesystems, you can control the operation of swap partitions by using
the
swapoff and
swapon
commands.
If you want to modify your swap partition, you may need to
temporarily turn off swapping. To do so, enter the command:
swapoff -a
This command turns off swapping on every swap device mentioned
in
/etc/fstab. If you want to turn off swapping on
a particular device, enter the command:
swapoff /dev/
device
where
device specifies the swap
device; for example,
hda3.
To turn on swapping, enter the command:
swapon -a
This command turns on swapping for all swap devices mentioned in
/etc/fstab. If you want to turn on swapping on a
particular device, enter the command:
swapon /dev/
device
where
device specifies the swap
device; for example,
hda3.
