enable/disable devices and files for paging and swapping
see also :
swapon - init - mkswap - mount
[-f] [-p priority]
swapoff [-v] specialfile...
[-e] [-f] [-v]
swapoff -a [-v]
add an example, a script, a trick and tips
sudo swapoff -a
sudo swapon -a
/sbin/swapoff -a &&
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
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
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.
/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
Use the partition that has the
specified label. (For this, access to
/proc/partitions is needed.)
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.
Display swap usage summary by
device. Equivalent to "cat /proc/swaps". Not
available before Linux 2.1.25.
Use the partition that has the
The swapon command is part of the util-linux package and is
available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
/dev/sd?? standard paging devices
/etc/fstab ascii filesystem description table
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.
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 command appeared in 4.0BSD.
swapoff, fstab, init ,
mkswap , rc, mount