Mastering the 'swapon' and 'swap' Linux Commands

Man working on computer in striped button up

vgajic / Getty Images

Swapon specifies the devices on which paging and file swapping will take place. Calls to swapon normally occur in the system multi-user initialization file /etc/rc that makes all swap devices available, so that the paging and swapping activity is interleaved across several devices and files.


/sbin/swapon [-h -V]
/sbin/swapon -a [-v] [-e]
/sbin/swapon [-v] [-p priorityspecialfile ...
/sbin/swapon [-s]
/sbin/swapoff [-h -V]
/sbin/swapoff -a
/sbin/swapoff specialfile ...  


Swapon supports several switches to extend or refine the command's execution.


Provide help


Display version


Display swap usage summary by device. Equivalent to cat /proc/swaps. Not available before Linux 2.1.25.


All devices marked as swap will swap devices in /etc/fstab are made available. Devices that are already running as swap are silently skipped.


When -a is used with swapon-e makes swapon silently skip devices that do not exist.

-p priority

Specify a priority for swapon. This option is only available if swapon was compiled under and is used under a 1.3.2 or later kernel. The priority is a value between 0 and 32767. Add pri=value to the option field of/etc/fstab for use with swapon -a.

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. 

Related commands include:

  • swapon(2)
  • swapoff(2)
  • init(8)
  • mkswap(8)
  • rc(8)
  • mount(8) 

The specific use of swapon may vary by distribution and kernel-release level. Use the man command (% man) to see how a command is used on your particular computer.