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diff --git a/sys-utils/swapon.8 b/sys-utils/swapon.8 new file mode 100644 index 0000000..510a15f --- /dev/null +++ b/sys-utils/swapon.8 @@ -0,0 +1,256 @@ +.\" Copyright (c) 1980, 1991 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. +.\" 3. All advertising materials mentioning features or use of this software +.\" must display the following acknowledgement: +.\" This product includes software developed by the University of +.\" California, Berkeley and its contributors. +.\" 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.8 6.3 (Berkeley) 3/16/91 +.\" +.TH SWAPON 8 "October 2014" "util-linux" "System Administration" +.SH NAME +swapon, swapoff \- enable/disable devices and files for paging and swapping +.SH SYNOPSIS +.B swapon +[options] +.RI [ specialfile ...] +.br +.B swapoff +.RB [ \-va ] +.RI [ specialfile ...] +.SH DESCRIPTION +.B swapon +is used to specify devices on which paging and swapping are to take place. + +The device or file used is given by the +.I specialfile +parameter. It may be of the form +.BI \-L " label" +or +.BI \-U " uuid" +to indicate a device by label or uuid. + +Calls to +.B swapon +normally occur in the system boot scripts making all swap devices available, so +that the paging and swapping activity is interleaved across several devices and +files. + +.B swapoff +disables swapping on the specified devices and files. +When the +.B \-a +flag is given, swapping is disabled on all known swap devices and files +(as found in +.I /proc/swaps +or +.IR /etc/fstab ). + +.SH OPTIONS +.TP +.BR \-a , " \-\-all" +All devices marked as ``swap'' in +.I /etc/fstab +are made available, except for those with the ``noauto'' option. +Devices that are already being used as swap are silently skipped. +.TP +.BR \-d , " \-\-discard" [ =\fIpolicy\fR] +Enable swap discards, if the swap backing device supports the discard or +trim operation. This may improve performance on some Solid State Devices, +but often it does not. The option allows one to select between two +available swap discard policies: +.B \-\-discard=once +to perform a single-time discard operation for the whole swap area at swapon; +or +.B \-\-discard=pages +to asynchronously discard freed swap pages before they are available for reuse. +If no policy is selected, the default behavior is to enable both discard types. +The +.I /etc/fstab +mount options +.BR discard , +.BR discard=once , +or +.B discard=pages +may also be used to enable discard flags. +.TP +.BR \-e , " \-\-ifexists" +Silently skip devices that do not exist. +The +.I /etc/fstab +mount option +.B nofail +may also be used to skip non-existing device. + +.TP +.BR \-f , " \-\-fixpgsz" +Reinitialize (exec mkswap) the swap space if its page size does not +match that of the current running kernel. +.BR mkswap (2) +initializes the whole device and does not check for bad blocks. +.TP +.BR \-h , " \-\-help" +Display help text and exit. +.TP +.BI \-L " label" +Use the partition that has the specified +.IR label . +(For this, access to +.I /proc/partitions +is needed.) +.TP +.BR \-o , " \-\-options " \fIopts\fP +Specify swap options by an fstab-compatible comma-separated string. +For example: +.RS +.RS +.sp +.B "swapon -o pri=1,discard=pages,nofail /dev/sda2" +.sp +.RE +The \fIopts\fP string is evaluated last and overrides all other +command line options. +.RE +.TP +.BR \-p , " \-\-priority " \fIpriority\fP +Specify the priority of the swap device. +.I priority +is a value between \-1 and 32767. Higher numbers indicate +higher priority. See +.BR swapon (2) +for a full description of swap priorities. Add +.BI pri= value +to the option field of +.I /etc/fstab +for use with +.BR "swapon -a" . +When no priority is defined, it defaults to \-1. +.TP +.BR \-s , " \-\-summary" +Display swap usage summary by device. Equivalent to "cat /proc/swaps". +This output format is DEPRECATED in favour +of \fB\-\-show\fR that provides better control on output data. +.TP +.BR \-\-show [ =\fIcolumn\fR ...] +Display a definable table of swap areas. See the +.B \-\-help +output for a list of available columns. +.TP +.B \-\-output\-all +Output all available columns. +.TP +.B \-\-noheadings +Do not print headings when displaying +.B \-\-show +output. +.TP +.B \-\-raw +Display +.B \-\-show +output without aligning table columns. +.TP +.B \-\-bytes +Display swap size in bytes in +.B \-\-show +output instead of in user-friendly units. +.TP +.BI \-U " uuid" +Use the partition that has the specified +.IR uuid . +.TP +.BR \-v , " \-\-verbose" +Be verbose. +.TP +.BR \-V , " \-\-version" +Display version information and exit. +.SH NOTES +You should not use \fBswapon\fR on a file with holes. +This can be seen in the system log as +.RS +.sp +.B "swapon: swapfile has holes." +.sp +.RE +The swap file implementation in the kernel expects to be able to write to the +file directly, without the assistance of the filesystem. This is a problem on +preallocated files (e.g. +.BR fallocate (1)) +on filesystems like \fBXFS\fR or \fBext4\fR, and on copy-on-write +filesystems like \fBbtrfs\fR. +.PP +It is recommended to use +.BR dd (1) +and +.I /dev/zero +to avoid holes on XFS and ext4. +.PP +.B swapon +may not work correctly when using a swap file with some versions of +\fBbtrfs\fR. This is due to btrfs being a copy-on-write filesystem: the +file location may not be static and corruption can result. Btrfs actively +disallows the use of swap files on its filesystems by refusing to map the file. +.PP +One possible workaround is to map the swap +file to a loopback device. This will allow the filesystem to determine the +mapping properly but may come with a performance impact. +.PP +Swap over \fBNFS\fR may not work. +.PP +.B swapon +automatically detects and rewrites a swap space signature with old software +suspend data (e.g. S1SUSPEND, S2SUSPEND, ...). The problem is that if we don't +do it, then we get data corruption the next time an attempt at unsuspending is +made. + +.SH ENVIRONMENT +.IP LIBMOUNT_DEBUG=all +enables libmount debug output. +.IP LIBBLKID_DEBUG=all +enables libblkid debug output. + +.SH SEE ALSO +.BR swapoff (2), +.BR swapon (2), +.BR fstab (5), +.BR init (8), +.BR mkswap (8), +.BR mount (8), +.BR rc (8) +.SH FILES +.br +.I /dev/sd?? +standard paging devices +.br +.I /etc/fstab +ascii filesystem description table +.SH HISTORY +The +.B swapon +command appeared in 4.0BSD. +.SH AVAILABILITY +The swapon command is part of the util-linux package and is available from +https://www.kernel.org/pub/linux/utils/util-linux/. |