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).
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.
-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.
-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 priprity
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/.