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).

To get swap information:

swapon -s [-h] [-V]

To enable a swap area:

swapon [-d] [-f] [-p priority] [-v] specialfile...

To disable a swap area:

swapoff [-v] specialfile...

To enable all swap areas:

swapon -a [-e] [-f] [-v]

To disable all swap areas:

swapoff -a [-v]

Options

Notes

You should not use swapon on a file with holes (not contiguously represented on disk). Swap over NFS may not work. swapon automatically detects and rewrites swap space signature with old software suspend data (e.g., S1SUSPEND, S2SUSPEND, ...); otherwise, you can get data corruption the next time an attempt at unsuspending is made.

The swapon command may not work correctly when using a swap file with some versions of btrfs (B-Tree file system). Because 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 problem can be seen in the system log as "swapon: swapfile has holes." One possible workaround is to map the file to a loopback device, which allows the file system to determine the mapping properly but may come with a performance impact.

swapon /dev/sdc1

Enable the swap partition /dev/sdc1.