-a

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

Enable swap discards, if the swap backing device supports the discard or trim operation. This mayimprove performance on some Solid State Devices, but often it does not. The option allows one toselect between two available swap discard policies: --discard=once to perform a single-time discardoperation for the whole swap area at swapon; or --discard=pages to asynchronously discard freed swappages before they are available for reuse. If no policy is selected, the default behavior is to enableboth discard types. The /etc/fstab mount options discard, discard=once, or discard=pages may also beused to enable discard flags.

-e

Silently skip devices that do not exist. The /etc/fstab mount option nofail may also be used to skipnon-existing device.

-f

Reinitialize (exec mkswap) the swap space if its page size does not match that of the current runningkernel. mkswap(2) initializes the whole device and does not check for bad blocks.

-h

Display help text and exit.

-L

Use the partition that has the specified label. (For this, access to /proc/partitions is needed.)

-o

Specify swap options by an fstab-compatible comma-separated string. For example:swapon -o pri=1,discard=pages,nofail /dev/sda2The opts string is evaluated last and overrides all other command line options.

-p

Specify the priority of the swap device. priority is a value between -1 and 32767. Higher numbersindicate higher priority. See swapon(2) for a full description of swap priorities. Add pri=value tothe option field of /etc/fstab for use with swapon -a. When no priority is defined, it defaults to -1.

-s

Display swap usage summary by device. Equivalent to "cat /proc/swaps". This output format is DEPRE‐CATED in favour of --show that provides better control on output data.

--show[

Display a definable table of swap areas. See the --help output for a list of 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

Use the partition that has the specified uuid.

-V

Display version information and exit.NOTESYou should not use swapon on a file with holes. This can be seen in the system log asswapon: swapfile has holes.The swap file implementation in the kernel expects to be able to write to the file directly, without theassistance of the filesystem. This is a problem on preallocated files (e.g. fallocate(1)) on filesystemslike XFS or ext4, and on copy-on-write filesystems like btrfs.It is recommended to use dd(1) and /dev/zero to avoid holes on XFS and ext4.swapon may not work correctly when using a swap file with some versions of btrfs. This is due to btrfs beinga copy-on-write filesystem: the file location may not be static and corruption can result. Btrfs activelydisallows the use of swap files on its filesystems by refusing to map the file.One possible workaround is to map the swap file to a loopback device. This will allow the filesystem todetermine the mapping properly but may come with a performance impact.Swap over NFS may not work.swapon automatically detects and rewrites a swap space signature with old software suspend data (e.g S1SUS‐PEND, S2SUSPEND, ...). The problem is that if we don't do it, then we get data corruption the next time anattempt at unsuspending is made.ENVIRONMENTLIBMOUNT_DEBUG=allenables libmount debug output.LIBBLKID_DEBUG=allenables libblkid debug output.