SWAPON
Section: System Administration (8)
Updated: September 1995
Index
Return to Main Contents
NAME
swapon, swapoff - enable/disable devices and files for paging and swapping
SYNOPSIS
Get info:
swapon -s
[-h]
[-V]
Enable/disable:
swapon
[-d]
[-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
-
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 discard flag.
- -e, --ifexists
-
Silently skip devices that do not exist.
The
/etc/fstab
mount option
nofail
may be also used to skip non-existing device.
- -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.
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.
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 package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- NOTES
-
- SEE ALSO
-
- FILES
-
- HISTORY
-
- AVAILABILITY
-
This document was created by
man2html,
using the manual pages.
Time: 13:52:45 GMT, May 19, 2024