swapon - Man Page

• Show swap information: swapon
• Enable a given swap area: sudo swapon path/to/file
• Enable all swap areas specified in /etc/fstab except those with the noauto option: sudo swapon [-a|--all]
• Enable a swap partition by its label: sudo swapon -L label

tldr.sh

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. See the Fstab Configuration section for more details.

-T,  --fstab path

Specifies an alternative fstab file for compatibility with mount(8). If path is a directory, then the files in the directory are sorted by strverscmp(3); files that start with "." or without an .fstab extension are ignored. The option can be specified more than once. This option is mostly designed for initramfs or chroot scripts where additional configuration is specified beyond standard system configuration.

-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.

-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 0 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, Linux kernel defaults to negative numbers.

-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.

--annotate[=when]

Adds an annotation to each column header name. Such an annotation can be shown as a tooltip by terminals that support this feature. The optional when argument can be always, never, or auto. If the argument is omitted, it defaults to auto, which means that annotations will only be used when the output goes to a terminal.

--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.

-h,  --help

Display help text and exit.

-V,  --version

Display version and exit.

The command swapon --all reads configuration from /etc/fstab (or from a file specified by the --fstab command line option). Only fstab entries with the filesystem type (3rd field) set to "swap" are relevant.

The option --options accepts values in the same form as can be specified in the fourth field in fstab.

swapoff has the following exit status values since v2.36:

0

success

2

system has insufficient memory to stop swapping (OOM)

4

swapoff(2) syscall failed for another reason

8

non-swapoff(2) 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

The swapon command appeared in 4.0BSD.

swapoff(2), swapon(2), fstab(5), init(8), fallocate(1), mkswap(8), mount(8), rc(8)

For bug reports, use the issue tracker.

The swapon command is part of the util-linux package which can be downloaded from Linux Kernel Archive.

bcc-swapin(8), btrfs(5), btrfs-filesystem(8), configuration.nix(5), efence(3), fstab(5), mkswap(8), mount(8), org.freedesktop.systemd1(5), proc_swaps(5), swapin.bt(8), swaplabel(8), swapon(2), systemd.swap(5).

The man page swapoff(8) is an alias of swapon(8).