swapon

Enable devices and files for paging and swapping.

Synopsis

swapon [options] device...
swapon -a [options]
swapon --show[=columns]
swapon -s

Operation

Calls swapon(2) to enable swapping on the specified device or file.

Enable mode

Enables swap on one or more specified devices/files. Priority and discard policy can be configured via flags or fstab-style options.

`--all` mode

Reads /etc/fstab for entries with type swap, enables each one. Entries with the noauto option are skipped. Already-active swap areas are silently skipped.

`--show` mode (display only)

Reads /proc/swaps and displays a formatted table of active swap areas.

Inputs

Source	Purpose
Device/file path	Target to enable as swap
`/etc/fstab`	Enumerate swap entries for `--all`
`/proc/swaps`	List active swap areas for `--show`/`-s`

Outputs

swapon(2) syscall to enable swap
stdout: swap area listing (--show, -s)

Syscalls

Syscall	Description
`swapon(2)`	Enable swapping on a device/file

Flags for swapon(2)

Flag	Value	Description
`SWAP_FLAG_PREFER`	`0x8000`	Priority is specified (OR’d with priority in lower 15 bits)
`SWAP_FLAG_PRIO_MASK`	`0x7fff`	Priority value mask (0-32767)
`SWAP_FLAG_DISCARD`	`0x10000`	Enable discard
`SWAP_FLAG_DISCARD_ONCE`	`0x20000`	Discard at swapon time
`SWAP_FLAG_DISCARD_PAGES`	`0x40000`	Discard freed page clusters

Command-line options

Option	Description
`-a, --all`	Enable all swap entries from /etc/fstab
`-d, --discard[=policy]`	Enable discard (once, pages, or both)
`-e, --ifexists`	Silently skip non-existent devices
`-p, --priority <N>`	Set swap priority (0-32767)
`-s, --summary`	Display /proc/swaps (deprecated)
`--show[=columns]`	Display formatted table of swap areas
`--noheadings`	Suppress table headers
`--bytes`	Show sizes in bytes
`-v, --verbose`	Verbose output
`-h, --help`	Display help
`-V, --version`	Display version

`--show` columns

NAME, TYPE, SIZE, USED, PRIO

Exit codes

Code	Meaning
0	Success
nonzero	Failure

Permissions

Requires CAP_SYS_ADMIN.

Not yet implemented

LABEL=, UUID=, PARTLABEL=, PARTUUID= device specifiers (needs libblkid)
-L, -U flags
-f, --fixpgsz (reinitialize swap on page size mismatch)
-o, --options (fstab-style option string)
-T, --fstab (alternative fstab)
--output-all, --raw output modes
Suspend data detection
Reading priority/discard from fstab options in --all mode

Keyboard shortcuts

linuxutils