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.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1995-07-22 by Michael Chastain <mec@duracef.shout.net>
.\" Modified 1995-07-23 by aeb
.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1998-09-08 by aeb
.\" Modified 2004-06-17 by Michael Kerrisk <mtk-manpages@gmx.net>
.\" Modified 2004-10-10 by aeb
.\" 2004-12-14 mtk, Anand Kumria: added new errors
.\"
.TH SWAPON 2 2004-10-10 "Linux 2.6.7" "Linux Programmer's Manual"
.SH NAME
swapon, swapoff \- start/stop swapping to file/device
.SH SYNOPSIS
.B #include <unistd.h>
.br
.B #include <asm/page.h> /* to find PAGE_SIZE */
.br
.B #include <sys/swap.h>
.sp
.BI "int swapon(const char *" path ", int " swapflags );
.br
.BI "int swapoff(const char *" path );
.SH DESCRIPTION
.BR swapon ()
sets the swap area to the file or block device specified by
.IR path .
.BR swapoff ()
stops swapping to the file or block device specified by
.IR path .
.PP
.BR swapon ()
takes a
.I swapflags
argument.
If
.I swapflags
has the
.I SWAP_FLAG_PREFER
bit turned on, the new swap area will have a higher priority than default.
The priority is encoded within
.I swapflags
as:
.br
.sp
.I " (prio << SWAP_FLAG_PRIO_SHIFT) & SWAP_FLAG_PRIO_MASK"
.br
.PP
These functions may only be used by a privileged process (one having the
.B CAP_SYS_ADMIN
capability).
.SH PRIORITY
Each swap area has a priority, either high or low.
The default priority is low.
Within the low-priority areas,
newer areas are even lower priority than older areas.
.PP
All priorities set with
.I swapflags
are high-priority, higher than default.
They may have any non-negative value chosen by the caller.
Higher numbers mean higher priority.
.PP
Swap pages are allocated from areas in priority order,
highest priority first.
For areas with different priorities,
a higher-priority area is exhausted before using a lower-priority area.
If two or more areas have the same priority,
and it is the highest priority available,
pages are allocated on a round-robin basis between them.
.PP
As of Linux 1.3.6, the kernel usually follows these rules,
but there are exceptions.
.SH "RETURN VALUE"
On success, zero is returned. On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EBUSY
.RB (for swapon ())
The specified
.I path
is already being used as a swap area.
.TP
.B EINVAL
The file
.I path
exists, but refers neither to a regular file nor to a block device;
or, for
.BR swapon (),
the indicated path does not contain a valid swap signature;
or, for
.BR swapoff (),
.I path
is not currently a swap area.
.TP
.B ENFILE
The system limit on the total number of open files has been reached.
.TP
.B ENOENT
The file
.I path
does not exist.
.TP
.B ENOMEM
The system has insufficient memory to start swapping.
.TP
.B EPERM
The caller does not have the
.B CAP_SYS_ADMIN
capability, or all
.B MAX_SWAPFILES
(earlier 8; 32 since Linux 2.4.10) are in use.
.SH "CONFORMING TO"
These functions are Linux specific and should not be used in programs
intended to be portable.
The second
.I swapflags
argument was introduced in Linux 1.3.2.
.SH NOTES
The partition or path must be prepared with
.BR mkswap (8).
.SH "SEE ALSO"
.BR mkswap (8),
.BR swapoff (8),
.BR swapon (8)
|
