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+.\" Copyright (c) 1980, 1991, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)swapon.2	8.1 (Berkeley) 6/4/93
+.\" $FreeBSD$
+.\"
+.Dd June 4, 1993
+.Dt SWAPON 2
+.Os
+.Sh NAME
+.Nm swapon , swapoff
+.Nd control devices for interleaved paging/swapping
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In unistd.h
+.Ft int
+.Fn swapon "const char *special"
+.Ft int
+.Fn swapoff "const char *special"
+.Sh DESCRIPTION
+The
+.Fn swapon
+system call
+makes the block device
+.Fa special
+available to the system for
+allocation for paging and swapping.
+The names of potentially
+available devices are known to the system and defined at system
+configuration time.
+The size of the swap area on
+.Fa special
+is calculated at the time the device is first made available
+for swapping.
+.Pp
+The
+.Fn swapoff
+system call disables paging and swapping on the given device.
+All associated swap metadata are deallocated, and the device
+is made available for other purposes.
+.Sh RETURN VALUES
+If an error has occurred, a value of -1 is returned and
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+Both
+.Fn swapon
+and
+.Fn swapoff
+can fail if:
+.Bl -tag -width Er
+.It Bq Er ENOTDIR
+A component of the path prefix is not a directory.
+.It Bq Er ENAMETOOLONG
+A component of a pathname exceeded 255 characters,
+or an entire path name exceeded 1023 characters.
+.It Bq Er ENOENT
+The named device does not exist.
+.It Bq Er EACCES
+Search permission is denied for a component of the path prefix.
+.It Bq Er ELOOP
+Too many symbolic links were encountered in translating the pathname.
+.It Bq Er EPERM
+The caller is not the super-user.
+.It Bq Er EFAULT
+The
+.Fa special
+argument
+points outside the process's allocated address space.
+.El
+.Pp
+Additionally,
+.Fn swapon
+can fail for the following reasons:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+The system has reached the boot-time limit on the number of
+swap devices,
+.Va vm.nswapdev .
+.It Bq Er ENOTBLK
+The
+.Fa special
+argument
+is not a block device.
+.It Bq Er EBUSY
+The device specified by
+.Fa special
+has already
+been made available for swapping
+.It Bq Er ENXIO
+The major device number of
+.Fa special
+is out of range (this indicates no device driver exists
+for the associated hardware).
+.It Bq Er EIO
+An I/O error occurred while opening the swap device.
+.El
+.Pp
+Lastly,
+.Fn swapoff
+can fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+The system is not currently swapping to
+.Fa special .
+.It Bq Er ENOMEM
+Not enough virtual memory is available to safely disable
+paging and swapping to the given device.
+.El
+.Sh SEE ALSO
+.Xr config 8 ,
+.Xr swapon 8 ,
+.Xr sysctl 8
+.Sh HISTORY
+The
+.Fn swapon
+system call appeared in
+.Bx 4.0 .
+The
+.Fn swapoff
+system call appeared in
+.Fx 5.0 .