From Linux Man Pages
swapon, swapoff - enable/disable devices and files for paging and swapping
SYNOPSIS
/sbin/swapon [-h -V]
/sbin/swapon -a [-v] [-e]
/sbin/swapon [-v] [-p priority] specialfile ...
/sbin/swapon [-s]
/sbin/swapoff [-h -V]
/sbin/swapoff -a
/sbin/swapoff specialfile ...
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 indi-
cate a device by label or uuid.
Calls to swapon normally occur in the system multi-user initialization file /etc/rc making all swap devices
available, so that the paging and swapping activity is interleaved across several devices and files.
Normally, the first form is used:
-a All devices marked as ``swap swap devices in /etc/fstab are made available, except for those with the
``noauto option. Devices that are already running as swap are silently skipped.
-e When -a is used with swapon, -e makes swapon silently skip devices that do not exist.
-h Provide help
-L label
Use the partition that has the specified label. (For this, access to /proc/partitions is needed.)
-p priority
Specify priority for swapon. This option is only available if swapon was compiled under and is used under
a 1.3.2 or later kernel. priority is a value between 0 and 32767. Higher numbers indicate higher prior-
ity. 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 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. (For this, access to /proc/partitions is needed.)
-v Be verbose.
-V Display version
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).
If loop=/dev/loop? and encryption=AES128 options are present in /etc/fstab then swapon -a will set up loop
devices using random keys, run mkswap on them, and enable encrypted swap on specified loop devices. Encrypted
loop devices are set up with page size offset so that unencrypted swap signatures on first page of swap devices
are not touched. swapoff -a will tear down such loop devices.
NOTE
You should not use swapon on a file with holes. Swap over NFS may not work.
RELATED
swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8)
FILES
/dev/hd?? standard paging devices
/dev/sd?? standard (SCSI) paging devices
/etc/fstab ascii filesystem description table
HISTORY
The swapon command appeared in 4.0BSD.
CATEGORY