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SWAPON(8) System Administration SWAPON(8)
swapon, swapoff - enable/disable devices and files for paging and
swapping
Get info:
swapon -s [-h] [-V]
Enable/disable:
swapon [-d] [-f] [-p priority] [-v] specialfile...
swapoff [-v] specialfile...
Enable/disable all:
swapon -a [-e] [-f] [-v]
swapoff -a [-v]
swapon is used to specify devices on which paging and swapping are to
take place.
The device or file used is given by the specialfile parameter. It may
be of the form -L label or -U uuid to indicate a device by label or
uuid.
Calls to swapon normally occur in the system boot scripts making all
swap devices available, so that the paging and swapping activity is
interleaved across several devices and files.
swapoff disables swapping on the specified devices and files. When
the -a flag is given, swapping is disabled on all known swap devices
and files (as found in /proc/swaps or /etc/fstab).
-a, --all
All devices marked as ``swap'' in /etc/fstab are made
available, except for those with the ``noauto'' option.
Devices that are already being used as swap are silently
skipped.
-d, --discard
Discard freed swap pages before they are reused, if the swap
device supports the discard or trim operation. This may
improve performance on some Solid State Devices, but often it
does not. The /etc/fstab mount option discard may be also
used to enable discard flag.
-e, --ifexists
Silently skip devices that do not exist. The /etc/fstab mount
option nofail may be also used to skip non-existing device.
-f, --fixpgsz
Reinitialize (exec /sbin/mkswap) the swap space if its page
size does not match that of the current running kernel.
mkswap(2) initializes the whole device and does not check for
bad blocks.
-h, --help
Provide help.
-L label
Use the partition that has the specified label. (For this,
access to /proc/partitions is needed.)
-p, --priority priority
Specify the priority of the swap device. priority is a value
between -1 and 32767. Higher numbers indicate higher
priority. See swapon(2) for a full description of swap
priorities. Add pri=value to the option field of /etc/fstab
for use with swapon -a. When priority is not defined it
defaults to -1.
-s, --summary
Display swap usage summary by device. Equivalent to "cat
/proc/swaps". Not available before Linux 2.1.25.
--show [column,column]
Display definable device table similar to --summary output.
See --help output for column list.
--noheadings
Do not print headings when displaying --show output.
--raw Display --show output without aligning table columns.
--bytes
Display swap size in bytes in --show output instead of user
friendly size and unit. -U uuid Use the partition that has
the specified uuid.
-v, --verbose
Be verbose.
-V, --version
Display version.
You should not use swapon on a file with holes. Swap over NFS may
not work.
swapon automatically detects and rewrites swap space signature with
old software suspend data (e.g S1SUSPEND, S2SUSPEND, ...). The
problem is that if we don't do it, then we get data corruption the
next time an attempt at unsuspending is made.
swapon may not work correctly when using a swap file with some
versions of btrfs. This is due to the swap file implementation in
the kernel expecting to be able to write to the file directly,
without the assistance of the file system. Since btrfs is a copy-on-
write file system, the file location may not be static and corruption
can result. Btrfs actively disallows the use of files on its file
systems by refusing to map the file. This can be seen in the system
log as "swapon: swapfile has holes." One possible workaround is to
map the file to a loopback device. This will allow the file system to
determine the mapping properly but may come with a performance
impact.
LIBMOUNT_DEBUG=0xffff
enables debug output.
swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8)
/dev/sd?? standard paging devices
/etc/fstab ascii filesystem description table
The swapon command appeared in 4.0BSD.
The swapon command is part of the util-linux package and is available
from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found at
[unknown--email man-pages@man7.org if you know]. It is not known how
to report bugs for this man page; if you know, please send a mail to
man-pages@man7.org. This page was obtained from the project's
upstream Git repository
(git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git) on
2013-07-05. If you discover any rendering problems in this HTML
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util-linux September 1995 SWAPON(8)
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