Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
SWAPON(8)		  BSD System Manager's Manual		     SWAPON(8)

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

     swapon [-F	fstab] -aLq | -E file ...
     swapoff [-F fstab]	-aLq | file ...
     swapctl [-AghklmsU] [-a file ... |	-d file	...]

     The swapon, swapoff and swapctl utilities are used	to control swap	de-
     vices 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 speci-
     fied, 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 an-
     other 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 op-
     tion is used, informational messages will not be written to standard out-
     put when a	swap device is removed.	 Note that swapoff will	fail and
     refuse to remove a	swap device if there is	insufficient VM	(memory	+ re-
     maining swap devices) to run the system.  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.

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

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

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

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

BSD				 May 19, 2020				   BSD


Want to link to this manual page? Use this URL:

home | help