229 lines
5.7 KiB
Groff
229 lines
5.7 KiB
Groff
.\" $OpenBSD: swapctl.8,v 1.36 2021/08/24 13:15:07 jmc Exp $
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.\" $NetBSD: swapctl.8,v 1.14 1998/05/22 18:27:52 msaitoh 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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.\"
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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 $Mdocdate: August 24 2021 $
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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 swapctl
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.Fl A
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.Op Fl p Ar priority
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.Op Fl t Cm blk | noblk
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.Nm swapctl
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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 swapctl
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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 swapctl
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.Fl d
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.Ar path
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.Nm swapctl
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.Op Oo Fl l Oc | Fl s
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.Op Fl k
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.Nm swapon
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.Fl a | 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
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.Ic swapctl -a ,
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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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it acts as
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.Ic swapctl -A .
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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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 an
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.Dq sw
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type, and adds all these entries
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as swap devices.
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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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.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 Ar path
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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 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 p Ar priority
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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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.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 Cm blk | noblk
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This flag modifies the function of the
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.Fl A
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option.
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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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.Cm 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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.Cm 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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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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.El
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.Sh SWAP OPTIONS
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Lines such as the following
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specify swap devices in
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.Pa /etc/fstab :
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.Bd -literal -offset indent
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/dev/sd1b none swap sw
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d48d0e3fc1c39531.k none swap sw
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.Ed
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.Pp
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The initial swap device (root disk, partition b) need not appear in
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.Pa /etc/fstab ,
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though it is not an error for it to do so.
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.Pp
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Additional flags include:
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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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Swap devices and files may be assigned different priorities,
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to allow 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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.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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Typically, once
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this mount has succeeded, the file to be used for swapping on will
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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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.Ex -std swapctl
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.Sh SEE ALSO
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.Xr swapctl 2 ,
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.Xr vnd 4 ,
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.Xr fstab 5 ,
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.Xr mount_nfs 8 ,
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.Xr mount_vnd 8
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.Sh HISTORY
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The
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.Nm
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program was originally developed in
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.Nx 1.3 .
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It was ported to
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.Ox 2.6
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by Tobias Weingartner.
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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 Mt mrg@eterna.com.au .
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.Sh BUGS
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Local and remote swap files cannot be configured until 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 one configures no
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local block swap devices on a machine that has local file systems to
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check and rely only on swap files, the machine will have no swap space
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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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