SWAPON(8)               FreeBSD System Manager's Manual              SWAPON(8)

NAME
     swapon, swapoff, swapctl - specify devices for paging and swapping

SYNOPSIS
     swapon [-F fstab] -aLq | -E file ...
     swapoff [-F fstab] -afLq | file ...
     swapctl [-AfghklmsU] [-a file ... | -d file ...]

DESCRIPTION
     The swapon, swapoff and swapctl utilities are used to control swap
     devices in the system.  At boot time all swap entries in /etc/fstab are
     added automatically when the system goes multi-user.  Swap devices use a
     fixed interleave; the maximum number of devices is unlimited.  There is
     no priority mechanism.

     The swapon utility adds the specified swap devices to the system.  If the
     -a option is used, all swap devices in /etc/fstab will be added, unless
     their "noauto" or "late" option is also set.  If the -L option is
     specified, swap devices with the "late" option will be added as well as
     ones with no option.  If the -q option is used, informational messages
     will not be written to standard output when a swap device is added.  The
     -E option causes each of following devices to receive a BIO_DELETE
     command.  This command marks the device's blocks as unused, except those
     that might store a disk label.  This marking can erase a crash dump.  To
     delay swapon for a device until after savecore has copied the crash dump
     to another location, use the "late" option.

     The swapoff utility removes the specified swap devices from the system.
     If the -a option is used, all swap devices in /etc/fstab will be removed,
     unless their "noauto" option is also set.  If the -L option is specified,
     only swap devices with the "late" option will be removed.  If the -q
     option is used, informational messages will not be written to standard
     output when a swap device is removed.  Note that swapoff will fail and
     refuse to remove a swap device if a very conservative check does not
     conclude that there is sufficient VM (memory + remaining swap devices) to
     run the system.  The -f option turns off this check, which could deadlock
     the system if there is insufficient swap space remaining.

     The swapoff utility must move swapped pages out of the device being
     removed which could lead to high system loads for a period of time,
     depending on how much data has been swapped out to that device.

     Other options supported by both swapon and swapoff are as follows:

     -F fstab
             Specify the fstab file to use (in conjunction with -a).

     The swapctl utility exists primarily for those familiar with other BSDs
     and may be used to add, remove, or list swap devices.  Note that the -a
     option is used differently in swapctl and indicates that a specific list
     of devices should be added.  The -d option indicates that a specific list
     should be removed.  The -A and -U options to swapctl operate on all swap
     entries in /etc/fstab which do not have their "noauto" option set.

     Swap information can be generated using the swapinfo(8) utility, pstat
     -s, or swapctl -l.  The swapctl utility has the following options for
     listing swap:

     -h      Output values in human-readable form.

     -g      Output values in gigabytes.

     -k      Output values in kilobytes.

     -m      Output values in megabytes.

     -l      List the devices making up system swap.

     -s      Print a summary line for system swap.

             The BLOCKSIZE environment variable is used if not specifically
             overridden.  512 byte blocks are used by default.

FILES
     /dev/{ada,da}?s?b      standard paging devices
     /dev/md?               memory disk devices
     /etc/fstab             ASCII file system description table

DIAGNOSTICS
     These utilities may fail for the reasons described in swapon(2).

SEE ALSO
     swapon(2), fstab(5), init(8), mdconfig(8), pstat(8), rc(8)

HISTORY
     The swapon utility appeared in 4.0BSD.  The swapoff and swapctl utilities
     appeared in FreeBSD 5.1.

FreeBSD 13.1-RELEASE-p6        November 29, 2021       FreeBSD 13.1-RELEASE-p6