swapon(8)

NAME

swapon, swapoff, swapctl - specify devices for paging and

swapping

SYNOPSIS

swapon -a | file ...
swapoff -a | file ...
swapctl [-AhklsU] [-a file ... | -d file ...]

DESCRIPTION

The swapon, swapoff and swapctl utilities are used to con

trol 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 specified

by the kernel configuration option NSWAPDEV, which is typically set to

4. 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'' option is also set.

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. Note that

swapoff will fail
and refuse to remove a swap device if there is insufficient

VM (memory +
remaining 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 da

ta has been
swapped out to that device.

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'' op

tion 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 megabytes.

-k Output values in kilobytes.

-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/{ad,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.

BSD December 28, 2002

BSD