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expression howmany(BBSIZE, PAGE_SIZE), where BBSIZE is the size of the boot block area. That can be less than 2 if PAGE_SIZE is big. swapon(8) has an option to trim (delete) all the blocks of a device at startup. However, if the first of those blocks is a bsd label, then trimming those blocks is destructive. Change swapon to leave the first BBSIZE bytes untrimmed. Update manual pages to reflect changes in how swapon and how it may be used, espeically in association with savecore. Reviewed by: alc Approved by: markj (mentor) MFC after: 3 days Differential Revision: https://reviews.freebsd.org/D21191
237 lines
5.5 KiB
Groff
237 lines
5.5 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. 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. 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 8.1 (Berkeley) 6/5/93
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.\" $FreeBSD$
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.\"
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.Dd June 21, 2019
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.Dt SWAPON 8
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.Os
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.Sh NAME
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.Nm swapon , swapoff , swapctl
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.Nd "specify devices for paging and swapping"
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.Sh SYNOPSIS
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.Nm swapon
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.Oo Fl F Ar fstab
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.Oc
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.Fl aLq | E Ar
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.Nm swapoff
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.Oo Fl F Ar fstab
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.Oc
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.Fl aLq | Ar
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.Nm swapctl
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.Op Fl AghklmsU
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.Oo
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.Fl a Ar
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.Fl d Ar
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.Oc
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.Sh DESCRIPTION
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The
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.Nm swapon , swapoff
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and
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.Nm swapctl
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utilities are used to control swap devices in the system.
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At boot time all swap entries in
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.Pa /etc/fstab
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are added automatically when the system goes multi-user.
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Swap devices use a fixed interleave; the maximum number of devices
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is unlimited.
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There is no priority mechanism.
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.Pp
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The
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.Nm swapon
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utility adds the specified swap devices to the system.
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If the
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.Fl a
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option is used, all swap devices in
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.Pa /etc/fstab
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will be added, unless their
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.Dq noauto
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or
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.Dq late
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option is also set.
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If the
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.Fl L
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option is specified,
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swap devices with the
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.Dq late
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option will be added as well as ones with no option.
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If the
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.Fl q
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option is used,
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informational messages will not be
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written to standard output when a swap device is added.
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The
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.Fl E
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option causes each of following devices to receive a
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.Dv BIO_DELETE
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command.
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This command marks the device's blocks as unused, except those that
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might store a disk label.
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This marking can erase a crash dump.
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To delay
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.Nm swapon
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for a device until after
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.Nm savecore
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has copied the crash dump to another location, use the
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.Dq late
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option.
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.Pp
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The
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.Nm swapoff
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utility removes the specified swap devices from the system.
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If the
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.Fl a
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option is used, all swap devices in
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.Pa /etc/fstab
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will be removed, unless their
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.Dq noauto
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option is also set.
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If the
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.Fl L
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option is specified,
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only swap devices with the
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.Dq late
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option will be removed.
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If the
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.Fl q
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option is used,
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informational messages will not be
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written to standard output when a swap device is removed.
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Note that
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.Nm swapoff
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will fail and refuse to remove a swap device if there is insufficient
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VM (memory + remaining swap devices) to run the system.
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The
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.Nm swapoff
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utility
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must move swapped pages out of the device being removed which could
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lead to high system loads for a period of time, depending on how
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much data has been swapped out to that device.
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.Pp
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Other options supported by both
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.Nm swapon
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and
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.Nm swapoff
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are as follows:
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.Bl -tag -width indent
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.It Fl F Ar fstab
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Specify the
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.Pa fstab
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file to use.
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.El
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.Pp
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The
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.Nm swapctl
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utility exists primarily for those familiar with other
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.Bx Ns s
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and may be
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used to add, remove, or list swap devices.
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Note that the
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.Fl a
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option is used differently in
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.Nm swapctl
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and indicates that a specific list of devices should be added.
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The
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.Fl d
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option indicates that a specific list should be removed.
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The
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.Fl A
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and
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.Fl U
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options to
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.Nm swapctl
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operate on all swap entries in
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.Pa /etc/fstab
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which do not have their
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.Dq noauto
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option set.
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.Pp
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Swap information can be generated using the
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.Xr swapinfo 8
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utility,
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.Nm pstat
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.Fl s ,
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or
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.Nm swapctl
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.Fl l .
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The
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.Nm swapctl
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utility has the following options for listing swap:
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.Bl -tag -width indent
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.It Fl h
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Output values in human-readable form.
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.It Fl g
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Output values in gigabytes.
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.It Fl k
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Output values in kilobytes.
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.It Fl m
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Output values in megabytes.
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.It Fl l
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List the devices making up system swap.
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.It Fl s
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Print a summary line for system swap.
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.Pp
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The
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.Ev BLOCKSIZE
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environment variable is used if not specifically
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overridden.
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512 byte blocks are used by default.
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.El
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.Sh FILES
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.Bl -tag -width ".Pa /dev/{ada,da}?s?b" -compact
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.It Pa /dev/{ada,da}?s?b
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standard paging devices
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.It Pa /dev/md?
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memory disk devices
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.It Pa /etc/fstab
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.Tn ASCII
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file system description table
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.El
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.Sh DIAGNOSTICS
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These utilities may fail for the reasons described in
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.Xr swapon 2 .
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.Sh SEE ALSO
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.Xr swapon 2 ,
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.Xr fstab 5 ,
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.Xr init 8 ,
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.Xr mdconfig 8 ,
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.Xr pstat 8 ,
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.Xr rc 8
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.Sh HISTORY
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The
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.Nm swapon
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utility appeared in
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.Bx 4.0 .
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The
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.Nm swapoff
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and
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.Nm swapctl
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utilities appeared in
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.Fx 5.1 .
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