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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | ENVIRONMENT | FILES | NOTES | HISTORY | SEE ALSO | AVAILABILITY | COLOPHON |
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SWAPON(8) System Administration SWAPON(8)
swapon, swapoff - enable/disable devices and files for paging and
swapping
swapon [options] [specialfile...]
swapoff [-va] [specialfile...]
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[=policy]
Enable swap discards, if the swap backing device supports
the discard or trim operation. This may improve
performance on some Solid State Devices, but often it does
not. The option allows one to select between two
available swap discard policies: --discard=once to perform
a single-time discard operation for the whole swap area at
swapon; or --discard=pages to asynchronously discard freed
swap pages before they are available for reuse. If no
policy is selected, the default behavior is to enable both
discard types. The /etc/fstab mount options discard,
discard=once, or discard=pages may also be used to enable
discard flags.
-e, --ifexists
Silently skip devices that do not exist. The /etc/fstab
mount option nofail may also be used to skip non-existing
device.
-f, --fixpgsz
Reinitialize (exec mkswap) the swap space if its page size
does not match that of the current running kernel.
mkswap(8) initializes the whole device and does not check
for bad blocks.
-h, --help
Display help text and exit.
-L label
Use the partition that has the specified label. (For
this, access to /proc/partitions is needed.)
-o, --options opts
Specify swap options by an fstab-compatible comma-
separated string. For example:
swapon -o pri=1,discard=pages,nofail /dev/sda2
The opts string is evaluated last and overrides all other
command line options.
-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 no priority is
defined, it defaults to -1.
-s, --summary
Display swap usage summary by device. Equivalent to "cat
/proc/swaps". This output format is DEPRECATED in favour
of --show that provides better control on output data.
--show[=column...]
Display a definable table of swap areas. See the --help
output for a list of available columns.
--output-all
Output all available columns.
--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 in
user-friendly units.
-U uuid
Use the partition that has the specified uuid.
-v, --verbose
Be verbose.
-V, --version
Display version information and exit.
swapoff has the following exit status values since v2.36:
0 success
2 system has insufficient memory to stop swapping (OOM)
4 swapoff syscall failed for another reason
8 non-swapoff syscall system error (out of memory, ...)
16 usage or syntax error
32 all swapoff failed on --all
64 some swapoff succeeded on --all
The command swapoff --all returns 0 (all succeeded), 32
(all failed), or 64 (some failed, some succeeded).
The old versions before v2.36 has no documented exit
status, 0 means success in all versions.
LIBMOUNT_DEBUG=all
enables libmount debug output.
LIBBLKID_DEBUG=all
enables libblkid debug output.
/dev/sd?? standard paging devices
/etc/fstab ascii filesystem description table
Files with holes
The swap file implementation in the kernel expects to be able to
write to the file directly, without the assistance of the
filesystem. This is a problem on files with holes or on copy-on-
write files on filesystems like Btrfs.
Commands like cp(1) or truncate(1) create files with holes.
These files will be rejected by swapon.
Preallocated files created by fallocate(1) may be interpreted as
files with holes too depending of the filesystem. Preallocated
swap files are supported on XFS since Linux 4.18.
The most portable solution to create a swap file is to use dd(1)
and /dev/zero.
Btrfs
Swap files on Btrfs are supported since Linux 5.0 on files with
nocow attribute. See the btrfs(5) manual page for more details.
NFS
Swap over NFS may not work.
Suspend
swapon automatically detects and rewrites a 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.
The swapon command appeared in 4.0BSD.
swapoff(2), swapon(2), fstab(5), init(8), fallocate(1),
mkswap(8), mount(8), rc(8)
The swapon command is part of the util-linux package and is
available from
https://www.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 ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you
have a bug report for this manual page, send it to
util-linux@vger.kernel.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
2020-12-18. (At that time, the date of the most recent commit
that was found in the repository was 2020-12-17.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
util-linux October 2014 SWAPON(8)
Pages that refer to this page: swapon(2), fstab(5), org.freedesktop.systemd1(5), proc(5), systemd.swap(5), mkswap(8), mount(8), swaplabel(8)
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