Provided by: mount_2.20.1-1ubuntu3_i386
swapon, swapoff - enable/disable devices and files for paging and
swapon -s [-h] [-V]
swapon [-d] [-f] [-p priority] [-v] specialfile...
swapoff [-v] specialfile...
swapon -a [-e] [-f] [-v]
swapoff -a [-v]
swapon is used to specify devices on which paging and swapping are to
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
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).
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.
Discard freed swap pages before they are reused, if the swap
device supports the discard or trim operation. This may improve
performance on some Solid State Devices, but often it does not.
The /etc/fstab mount option discard may be also used to enable
Silently skip devices that do not exist. The /etc/fstab mount
option nofail may be also used to skip non-existing device.
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
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
Display swap usage summary by device. Equivalent to "cat
/proc/swaps". Not available before Linux 2.1.25.
Use the partition that has the specified uuid.
You should not use swapon on a file with holes. Swap over NFS may not
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.
swapon may not work correctly when using a swap file with some versions
of btrfs. This is due to the swap file implementation in the kernel
expecting to be able to write to the file directly, without the
assistance of the file system. Since btrfs is a copy-on-write file
system, the file location may not be static and corruption can result.
Btrfs actively disallows the use of files on its file systems by
refusing to map the file. This can be seen in the system log as
"swapon: swapfile has holes." One possible workaround is to map the
file to a loopback device. This will allow the file system to determine
the mapping properly but may come with a performance impact.
swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8)
/dev/sd?? standard paging devices
/etc/fstab ascii filesystem description table
The swapon command appeared in 4.0BSD.
The swapon command is part of the util-linux package and is available