NAME¶

swapon, swapoff - enable/disable devices and files for paging and swapping

SYNOPSIS¶

Get info:

swapon -s [-h] [-V]

Enable/disable:

swapon [-f] [-p priority] [-v] specialfile...
swapoff [-v] specialfile...

Enable/disable all:

swapon -a [-e] [-f] [-v]
swapoff -a [-v]

DESCRIPTION¶

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 discard freed swap pages before they are reused, while swapping. 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 be also used to enable discard flags.

-e, --ifexists

Silently skip devices that do not exist.

-f, --fixpgsz

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

-h, --help

Provide help.

-L label

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

-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.

-s, --summary

Display swap usage summary by device. Equivalent to "cat /proc/swaps". Not available before Linux 2.1.25.

-U uuid

Use the partition that has the specified uuid.

-v, --verbose

Be verbose.

-V, --version

Display version.

NOTES¶

You should not use swapon on a file with holes. Swap over NFS may not work.

swapon automatically detects and rewrites 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.

SEE ALSO¶

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

FILES¶

/dev/sd?? standard paging devices
/etc/fstab ascii filesystem description table

HISTORY¶

The swapon command appeared in 4.0BSD.

AVAILABILITY¶

The swapon command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.