NAME
swapon, swapoff - enable/disable devices and files for paging and swappingSYNOPSIS
swapon [options] [specialfile...]DESCRIPTION
swapon is used to specify devices on which paging and swapping are to take place.OPTIONS
-a, --allAll 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.
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
--discard=pages
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.
to perform a single-time discard operation for
the whole swap area at swapon; or
to asynchronously discard freed swap pages
before they are available for reuse.
Silently skip devices that do not exist. The
/etc/fstab mount option nofail may also be used to skip
non-existing device.
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.
Use the partition that has the specified
label. (For this, access to /proc/partitions is needed.)
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.
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.
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.
Display a definable table of swap areas. See
the --help output for a list of available columns.
Output all available columns.
Do not print headings when displaying
--show output.
Display --show output without aligning
table columns.
Display swap size in bytes in --show
output instead of in user-friendly units.
Use the partition that has the specified
uuid.
Be verbose.
Display help text and exit.
Print version and exit.
EXIT STATUS
swapoff has the following exit status values since v2.36:success
system has insufficient memory to stop
swapping (OOM)
swapoff(2) syscall failed for another
reason
non-swapoff(2) syscall system error
(out of memory, ...)
usage or syntax error
all swapoff failed on --all
some swapoff succeeded on --all
ENVIRONMENT
LIBMOUNT_DEBUG=allenables libmount debug output.
enables libblkid debug output.
FILES
/dev/sd??standard paging devices
ascii filesystem description table
NOTES
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.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.HISTORY
The swapon command appeared in 4.0BSD.SEE ALSO
swapoff(2), swapon(2), fstab(5), init(8), fallocate(1), mkswap(8), mount(8), rc(8)REPORTING BUGS
For bug reports, use the issue tracker at <https://github.com/util-linux/util-linux/issues>.AVAILABILITY
The swapon command is part of the util-linux package which can be downloaded from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils/util-linux/>.2022-05-11 | util-linux 2.38.1 |