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.\"     @(#)swapon.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt SWAPON 2
.Os BSD 4
.Sh NAME
.Nm swapon
.Nd add a swap device for interleaved paging/swapping
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn swapon "const char *special"
.Sh DESCRIPTION
.Fn Swapon
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.
.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
.Fn Swapon
succeeds unless:
.Bl -tag -width ENAMETOOLONG
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er EINVAL
The pathname contains a character with the high-order bit set.
.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 ENOTBLK
.Fa Special
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 EINVAL
The device configured by
.Fa special
was not
configured into the system as a swap device.
.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.
.It Bq Er EFAULT
.Fa Special
points outside the process's allocated address space.
.Sh SEE ALSO
.Xr swapon 8 ,
.Xr config 8
.Sh BUGS
There is no way to stop swapping on a disk so that the pack may be
dismounted.
.Pp
This call will be upgraded in future versions of the system.
.Sh HISTORY
The
.Fn swapon
function call appeared in
.Bx 4.0 .