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.\"     @(#)swapon.8	8.1 (Berkeley) 6/5/93
.\" $FreeBSD$
.\"
.Dd June 5, 1993
.Dt SWAPON 8
.Os
.Sh NAME
.Nm swapon , swapoff
.Nd "specify devices for paging and swapping"
.Sh SYNOPSIS
.Nm swap[on|off]
.Fl a
.Nm swap[on|off]
.Ar special_file ...
.Nm swapctl
.Fl lshk
.Nm swapctl
.Fl AU
.Nm swapctl
.Fl a
.Ar special_file ...
.Nm swapctl
.Fl d
.Ar special_file ...
.Sh DESCRIPTION
The
.Nm swap[on,off,ctl]
utilties are used to control swap devices in the system.  At boot time all
swap entries in 
.Pa /etc/fstab
are added automatically when the system goes multi-user.
Swap devices are interleaved and kernels are typically configured
to handle a maximum of 4 swap devices.  There is no priority mechanism.
.Pp
The
.Nm swapon
utility adds the specified swap devices to the system.  If the
.Fl a
option is used, all swap devices in
.Pa /etc/fstab
will be added, unless their ``noauto'' option is also set.
.Pp
The
.Nm swapoff
utility removes the specified swap devices from the system.  If the
.Fl a
option is used, all swap devices in
.Pa /etc/fstab
will be removed, unless their ``noauto'' option is also set.
Note that
.Nm swapoff
will fail and refuse to remove a swap device if there is insufficient
VM (memory + remaining swap devices) to run the system.
.Nm Swapoff
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.
.Pp
The
.Nm swapctl
utility exists primarily for those familiar with other BSDs and may be
used to add, remove, or list swap.  Note that the
.Fl a
option is used diferently in
.Nm swapctl
and indicates that a specific list of devices should be added.
The 
.Fl d
option indicates that a specific list should be removed.  The
.Fl A
and 
.Fl D
options to
.Nm swapctl
operate on all swap entries in
.Pa /etc/fstab
which do not have their ``noauto'' option set.
.Pp
Swap information can be generated using the
.Nm swapinfo
program,
.Nm pstat
.Fl s ,
or
.Nm swapctl
.Fl lshk .
The
.Nm swapctl
utility has the following options for listing swap:
.Bl -tag -width indent
.It Fl l
List the devices making up system swap.
.It Fl s
Print a summary line for system swap.
.It Fl h
Output values in megabytes.
.It Fl k
Output values in kilobytes.
.Pp
The BLOCKSIZE environment variable is used if not specifically
overridden.  512 byte blocks are used by default.
.El
.Sh SEE ALSO
.Xr swapon 2 ,
.Xr fstab 5 ,
.Xr init 8 ,
.Xr mdconfig 8 ,
.Xr pstat 8 ,
.Xr rc 8
.Sh FILES
.Bl -tag -width "/dev/{ad,da}?s?b" -compact
.It Pa /dev/{ad,da}?s?b
standard paging devices
.It Pa /dev/md?
memory disk devices
.It Pa /etc/fstab
ASCII file system description table
.El
.Sh HISTORY
The
.Nm swapon
utility appeared in
.Bx 4.0 .
The
.Nm swapoff
utility appeared in
.Fx 5.0 .