Provided by: loop-aes-utils_2.16.2-2ubuntu1_amd64
swapon, swapoff - enable/disable devices and files for paging and swapping
Get info: swapon -s [-h] [-V] Enable/disable: swapon [-f] [-p priority] [-v] specialfile... swapoff [-v] specialfile... Enable/disable all: swapon -a [-e] [-f] [-v] swapoff -a [-v]
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). If loop=/dev/loop? and encryption=AES128 options are present in /etc/fstab then swapon -a will set up loop devices using random keys, run mkswap on them, and enable encrypted swap on specified loop devices. Encrypted loop devices are set up with page size offset so that unencrypted swap signatures on first page of swap devices are not touched. swapoff -a will tear down such loop devices. -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. -e, --ifexists Silently skip devices that do not exist. -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 priprity 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.
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.
/dev/sd?? standard paging devices /etc/fstab ascii filesystem description table
The swapon command appeared in 4.0BSD.
The swapon command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.