229 lines
7.1 KiB
Groff
229 lines
7.1 KiB
Groff
.\" Copyright (c) 1980, 1991 Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)swapon.8 6.3 (Berkeley) 3/16/91
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.\"
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.\" Sun Dec 27 12:31:30 1992: Modified by faith@cs.unc.edu
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.\" Sat Mar 6 20:46:02 1993: Modified by faith@cs.unc.edu
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.\" Sat Oct 9 09:35:30 1993: Converted to man format by faith@cs.unc.edu
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.\" Sat Nov 27 20:22:42 1993: Updated authorship information, faith@cs.unc.edu
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.\" Mon Sep 25 14:12:38 1995: Added -v and -p information
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.\" Tue Apr 30 03:32:07 1996: Added some text from A. Koppenhoefer
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.\"
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.TH SWAPON 8 "September 1995" "util-linux" "System Administration"
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.SH NAME
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swapon, swapoff \- enable/disable devices and files for paging and swapping
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.SH SYNOPSIS
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.B swapon
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[ options ]
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.RI [ specialfile... ]
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.br
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.B swapoff
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.RB [ \-va ]
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.RI [ specialfile... ]
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.SH DESCRIPTION
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.B swapon
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is used to specify devices on which paging and swapping are to take place.
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The device or file used is given by the
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.I specialfile
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parameter. It may be of the form
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.BI \-L " label"
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or
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.BI \-U " uuid"
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to indicate a device by label or uuid.
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Calls to
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.B swapon
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normally occur in the system boot scripts making all swap devices available, so
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that the paging and swapping activity is interleaved across several devices and
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files.
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.B swapoff
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disables swapping on the specified devices and files.
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When the
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.B \-a
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flag is given, swapping is disabled on all known swap devices and files
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(as found in
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.I /proc/swaps
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or
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.IR /etc/fstab ).
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.TP
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.B "\-a, \-\-all"
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All devices marked as ``swap'' in
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.I /etc/fstab
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are made available, except for those with the ``noauto'' option.
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Devices that are already being used as swap are silently skipped.
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.TP
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.B "\-d, \-\-discard\fR [=\fIpolicy\fR]"
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Enable swap discards, if the swap backing device supports the discard or
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trim operation. This may improve performance on some Solid State Devices,
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but often it does not. The option allows one to select between two
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available swap discard policies:
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.BI \-\-discard=once
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to perform a single-time discard operation for the whole swap area at swapon;
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or
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.BI \-\-discard=pages
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to discard freed swap pages before they are reused, while swapping.
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If no policy is selected, the default behavior is to enable both discard types.
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The
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.I /etc/fstab
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mount options
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.BI discard,
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.BI discard=once,
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or
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.BI discard=pages
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may be also used to enable discard flags.
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.TP
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.B "\-e, \-\-ifexists"
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Silently skip devices that do not exist.
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The
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.I /etc/fstab
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mount option
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.BI nofail
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may be also used to skip non-existing device.
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.TP
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.B "\-f, \-\-fixpgsz"
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Reinitialize (exec /sbin/mkswap) the swap space if its page size does not
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match that of the current running kernel.
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.BR mkswap (2)
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initializes the whole device and does not check for bad blocks.
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.TP
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.B \-h, \-\-help
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Display help text and exit.
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.TP
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.B "\-L \fIlabel\fP"
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Use the partition that has the specified
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.IR label .
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(For this, access to
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.I /proc/partitions
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is needed.)
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.TP
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.B "\-p, \-\-priority \fIpriority\fP"
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Specify the priority of the swap device.
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.I priority
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is a value between \-1 and 32767. Higher numbers indicate
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higher priority. See
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.BR swapon (2)
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for a full description of swap priorities. Add
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.BI pri= value
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to the option field of
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.I /etc/fstab
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for use with
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.BR "swapon -a" .
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When priority is not defined it defaults to \-1.
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.TP
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.B "\-s, \-\-summary"
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Display swap usage summary by device. Equivalent to "cat /proc/swaps".
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Not available before Linux 2.1.25.
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.TP
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\fB\-\-show\fR [\fIcolumn\fR, ...]
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Display definable device table similar to
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.B \-\-summary
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output. See \-\-help output for
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.I column
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list.
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.TP
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.B \-\-noheadings
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Do not print headings when displaying
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.B \-\-show
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output.
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.TP
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.B \-\-raw
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Display
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.B \-\-show
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output without aligning table columns.
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.TP
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.B \-\-bytes
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Display swap size in bytes in
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.B \-\-show
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output instead of user friendly size and unit.
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.B "\-U \fIuuid\fP"
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Use the partition that has the specified
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.IR uuid .
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.TP
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.B "\-v, \-\-verbose"
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Be verbose.
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.TP
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.B "\-V, \-\-version"
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Display version information and exit.
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.SH NOTES
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You should not use
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.B swapon
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on a file with holes.
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Swap over NFS may not work.
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.PP
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.B swapon
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automatically detects and rewrites swap space signature with old software
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suspend data (e.g S1SUSPEND, S2SUSPEND, ...). The problem is that if we don't
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do it, then we get data corruption the next time an attempt at unsuspending is
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made.
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.PP
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.B swapon
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may not work correctly when using a swap file with some versions of btrfs.
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This is due to the swap file implementation in the kernel expecting to be able
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to write to the file directly, without the assistance of the file system.
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Since btrfs is a copy-on-write file system, the file location may not be
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static and corruption can result. Btrfs actively disallows the use of files
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on its file systems by refusing to map the file. This can be seen in the system
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log as "swapon: swapfile has holes." One possible workaround is to map the
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file to a loopback device. This will allow the file system to determine the
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mapping properly but may come with a performance impact.
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.SH ENVIRONMENT
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.IP LIBMOUNT_DEBUG=0xffff
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enables debug output.
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.SH SEE ALSO
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.BR swapon (2),
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.BR swapoff (2),
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.BR fstab (5),
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.BR init (8),
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.BR mkswap (8),
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.BR rc (8),
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.BR mount (8)
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.SH FILES
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.br
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.I /dev/sd??
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standard paging devices
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.br
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.I /etc/fstab
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ascii filesystem description table
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.SH HISTORY
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The
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.B swapon
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command appeared in 4.0BSD.
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.SH AVAILABILITY
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The swapon command is part of the util-linux package and is available from
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ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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