392 lines
9.1 KiB
Groff
392 lines
9.1 KiB
Groff
.\" $NetBSD: swapctl.8,v 1.39 2007/08/02 18:53:46 he Exp $
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.\"
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.\" Copyright (c) 1997 Matthew R. Green
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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. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" 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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.Dd August 2, 2007
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.Dt SWAPCTL 8
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.Os
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.Sh NAME
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.Nm swapctl ,
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.Nm swapon
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.Nd system swap management tool
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.Sh SYNOPSIS
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.Nm
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.Fl A
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.Op Fl f | Fl o
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.Op Fl n
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.Op Fl p Ar priority
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.Op Fl t Ar blk|noblk|auto
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.Nm
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.Fl D Ar dumpdev|none
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.Nm
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.Fl U
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.Op Fl n
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.Op Fl t Ar blk|noblk|auto
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.Nm
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.Fl a
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.Op Fl p Ar priority
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.Ar path
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.Nm
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.Fl c
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.Fl p Ar priority
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.Ar path
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.Nm
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.Fl d
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.Ar path
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.Nm
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.Fl l | Fl s
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.Op Fl k | Fl m | Fl g | Fl h
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.Nm
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.Fl q
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.Nm
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.Fl z
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.Nm swapon
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.Fl a
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.Op Fl t Ar blk|noblk
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.Nm swapon
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.Ar path
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.Sh DESCRIPTION
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The
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.Nm
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program adds, removes,
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lists and prioritizes swap devices and files for the system.
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The
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.Nm swapon
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program acts the same as the
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.Nm
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program, as if called with the
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.Fl a
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option, except if
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.Nm swapon
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itself is called with
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.Fl a
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in which case,
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.Nm swapon
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acts as
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.Nm
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with the
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.Fl A
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option.
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.Pp
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The following options are available:
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.Bl -tag -width 123456
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.It Fl A
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This option causes
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.Nm
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to read the
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.Pa /etc/fstab
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file for devices and files with a
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.Dq sw
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or
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.Dq dp
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type, and adds all
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.Dq sw
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type entries as swap devices and sets the last
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.Dq dp
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type entry as the dump device.
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If no swap devices are configured,
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.Nm
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will exit with an error code.
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If used together with
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.Fl t Ar auto
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this option will not read
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.Pa /etc/fstab
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but query the kernel for all swap partitions on local hard disks.
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.It Fl a
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The
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.Fl a
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option requires that a
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.Ar path
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also be in the argument list.
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The
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.Ar path
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is added to the kernel's list of swap devices using the
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.Xr swapctl 2
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system call.
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When using the
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.Nm swapon
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form of this command, the
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.Fl a
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option is treated the same as the
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.Fl A
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option, for backwards compatibility.
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.It Fl c
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The
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.Fl c
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option changes the priority of the listed swap device or file.
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.It Fl D
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The
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.Fl D
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option requires that a
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.Ar dumpdev
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also be in the argument list.
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The kernel dump device is set to
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.Ar dumpdev .
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The word
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.Dq none
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can be used instead of a
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.Ar dumpdev
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to disable the currently set dump device.
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This change is made via the
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.Xr swapctl 2
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system call.
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The dump device is used when the system crashes
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to write a current snapshot of real memory, to be saved later with
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.Xr savecore 8
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at system reboot, and analyzed to determine the problem.
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.It Fl d
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The
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.Fl d
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option removes the listed
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.Ar path
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from the kernel's list of swap devices or files.
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.It Fl f
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Used in combination with the
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.Fl A
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command and
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.Fl t Ar auto
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flag this option makes
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.Nm
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use the first discovered swap device to also become the dump device.
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The
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.Fl f
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option is mutually exclusive with the
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.Fl o
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option.
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.It Fl g
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The
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.Fl g
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option uses (1024 * 1024 * 1024) byte blocks instead of the default 512 byte.
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.It Fl h
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The
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.Fl h
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option uses
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.Xr humanize_number 3
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to display the sizes.
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.It Fl k
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The
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.Fl k
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option uses 1024 byte blocks instead of the default 512 byte.
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.It Fl l
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The
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.Fl l
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option lists the current swap devices and files, and their usage statistics.
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.It Fl m
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The
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.Fl m
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option uses (1024 * 1024) byte blocks instead of the default 512 byte.
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.It Fl n
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Used with the
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.Fl A
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or
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.Fl U
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command, the
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.Fl n
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option makes
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.Nm
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print the action it would take, but not actually change any swap or
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dump devices.
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.It Fl o
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Similar to the
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.Fl f
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flag, this
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.Dq Dump Only
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option makes
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.Nm
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find the first swap device and configure it as dump device.
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No swap device is changed.
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This option needs to be used in combination with
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.Fl A Fl t Ar auto
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and is mutually exclusive with
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.Fl f .
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.It Fl p
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The
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.Fl p
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option sets the priority of swap devices or files to the
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.Ar priority
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argument.
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This works with the
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.\" .Fl d ,
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.Fl a ,
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.Fl c ,
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and
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.Fl l
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options.
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.It Fl q
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Query
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.Pa /etc/fstab ,
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checking for any defined swap or dump devices.
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If any are found,
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.Nm
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returns with an exit status of 0, if none are found the exit status will
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be 1.
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.It Fl s
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The
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.Fl s
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option displays a single line summary of current swap statistics.
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.It Fl t
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This flag modifies the function of the
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.Fl A
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and
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.Fl U
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options.
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The
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.Fl t
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option allows the type of device to add to be specified.
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An argument of
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.Ar blk
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causes all block devices in
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.Pa /etc/fstab
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to be added.
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An argument of
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.Ar noblk
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causes all non-block devices in
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.Pa /etc/fstab
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to be added.
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An argument of
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.Ar auto
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causes all swap partitions on local hard disks to be used.
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This option is useful in early system startup, where swapping
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may be needed before all file systems are available, such as during
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disk checks of large file systems.
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.It Fl U
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This option causes
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.Nm
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to read the
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.Pa /etc/fstab
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file for devices and files with a
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.Dq sw
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type, and remove all these entries as swap devices.
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If no swap devices are unconfigured,
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.Nm
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will exit with an error code.
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If used together with
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.Fl t Ar auto
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this option will not read
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.Pa /etc/fstab
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but unconfigure all local swap partitions.
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.It Fl z
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The
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.Fl z
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option displays the current dump device.
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.El
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.Sh SWAP PRIORITY
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The
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.Nx
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swap system allows different swap devices and files to be assigned different
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priorities, to allow the faster resources to be used first.
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Swap devices at the same priority are used in a round-robin fashion until
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there is no more space available at this priority, when the next priority
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level will be used.
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The default priority is 0, the highest.
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This value can be any valid integer,
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with higher values receiving less priority.
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.Sh SWAP OPTIONS
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When parsing the
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.Pa /etc/fstab
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file for swap devices, the following options are recognized:
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.Pp
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.Bl -tag -width nfsmntpt=/path -compact
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.It priority=N
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This option sets the priority of the specified swap device to N.
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.It nfsmntpt=/path
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This option is useful for swapping to NFS files.
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It specifies the local mount point to mount an NFS filesystem.
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The mount point must exist as a directory.
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Typically, once this mount has succeeded, the file to be used for swapping
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on will be available under this point mount.
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For example:
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.Bd -literal
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server:/export/swap/client none swap sw,nfsmntpt=/swap
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.Ed
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.El
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.Sh EXIT STATUS
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If the requested operation was sucessful, the
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.Nm
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utility exits with status 0.
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If an error occurred, the exit status is 1.
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.Pp
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For easy scriptability, the
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.Fl z
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operation (query dump device) and
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.Fl l
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(list swap partitions) return an exit status of 1 if no dump device or
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swap partition has been configured.
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If any swap partition is available or
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a dump device is set, the respective query returns 0.
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.Sh SEE ALSO
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.Xr swapctl 2 ,
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.Xr fstab 5 ,
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.Xr mount_nfs 8
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.Sh HISTORY
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The
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.Nm
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program was first made available in
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.Nx 1.3 .
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The original
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.Nm swapon
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program, provided for backwards compatibility, appeared in
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.Bx 4.0 .
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.Sh AUTHORS
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The
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.Nm
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program was written by
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.An Matthew R. Green Aq mrg@eterna.com.au .
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.Sh CAVEATS
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Using the automatic swap partition detection done by the
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.Fl A Fl t Ar auto
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option may be dangereous.
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Depending on the on-disk partitioning scheme used, the type of a partition
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may not be accurately recognizable as a swap partition.
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The autodetection might recognize and use partitions on
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removable media like USB sticks.
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An easy way to test the autoconfiguration is to use
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.Nm
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with the
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.Fl n
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option.
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.Sh BUGS
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If no swap information is specified in
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.Pa /etc/fstab ,
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the system startup scripts (see
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.Xr rc 8 )
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will configure no swap space and your machine will behave very badly
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if (more likely when) it runs out of real memory.
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.Pp
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Local and remote swap files cannot be configured until after the file
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systems they reside on are mounted read/write.
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The system startup scripts need to
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.Xr fsck 8
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all local file systems before this can happen.
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This process requires substantial amounts of memory on some systems.
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If you configure no local block swap devices on a machine that has local
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file systems to check and rely only on swap files, the machine will have
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no swap space at all during system
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.Xr fsck 8
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and may run out of real memory, causing fsck to abnormally exit and
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startup scripts to fail.
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