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diff --git a/sys-utils/swapon.8 b/sys-utils/swapon.8 new file mode 100644 index 0000000..486e028 --- /dev/null +++ b/sys-utils/swapon.8 @@ -0,0 +1,280 @@ +.\" 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 (8) +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 EXIT STATUS +.B swapoff +has the following exit status values since v2.36: +.TP +.B 0 +success +.TP +.B 2 +system has insufficient memory to stop swapping (OOM) +.TP +.B 4 +swapoff syscall failed for another reason +.TP +.B 8 +non-swapoff syscall system error (out of memory, ...) +.TP +.B 16 +usage or syntax error +.TP +.B 32 +all swapoff failed on \fB\-\-all\fR +.TP +.B 64 +some swapoff succeeded on \fB\-\-all\fR + +The command \fBswapoff \-\-all\fR returns 0 (all succeeded), 32 (all failed), or 64 (some +failed, some succeeded). + +The old versions before v2.36 has no documented exit status, 0 means success in all versions. + +.SH ENVIRONMENT +.IP LIBMOUNT_DEBUG=all +enables libmount debug output. +.IP LIBBLKID_DEBUG=all +enables libblkid debug output. + +.SH FILES +.I /dev/sd?? +standard paging devices +.br +.I /etc/fstab +ascii filesystem description table +.SH NOTES +.SS Files with holes +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 +files with holes or on copy-on-write files on filesystems like Btrfs. +.sp +Commands like +.BR cp (1) +or +.BR truncate (1) +create files with holes. These files will be rejected by swapon. +.sp +Preallocated files created by +.BR fallocate (1) +may be interpreted as files with holes too depending of the filesystem. +Preallocated swap files are supported on XFS since Linux 4.18. +.sp +The most portable solution to create a swap file is to use +.BR dd (1) +and /dev/zero. +.SS Btrfs +Swap files on Btrfs are supported since Linux 5.0 on files with nocow attribute. +See the +.BR btrfs (5) +manual page for more details. +.SS NFS +Swap over \fBNFS\fR may not work. +.SS Suspend +.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 HISTORY +The +.B swapon +command appeared in 4.0BSD. +.SH SEE ALSO +.BR swapoff (2), +.BR swapon (2), +.BR fstab (5), +.BR init (8), +.BR fallocate (1), +.BR mkswap (8), +.BR mount (8), +.BR rc (8) +.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/. |