swapon - Unix, Linux Command

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swapon, swapoff - enable/disable devices and files for paging and swapping


/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 ...


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 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 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 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).


You should not use swapon on a file with holes. Swap over NFS may not work.


/dev/hd?? standard paging devices
/dev/sd?? standard (SCSI) paging devices
/etc/fstab ascii filesystem description table


The swapon command appeared in 4.0BSD.
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