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swapon.c
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Editing: swapon.8
.\" Copyright (c) 1980, 1991, 1993 .\" The 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. 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 8.1 (Berkeley) 6/5/93 .\" $FreeBSD$ .\" .Dd May 19, 2020 .Dt SWAPON 8 .Os .Sh NAME .Nm swapon , swapoff , swapctl .Nd "specify devices for paging and swapping" .Sh SYNOPSIS .Nm swapon .Oo Fl F Ar fstab .Oc .Fl aLq | E Ar .Nm swapoff .Oo Fl F Ar fstab .Oc .Fl aLq | Ar .Nm swapctl .Op Fl AghklmsU .Oo .Fl a Ar | .Fl d Ar .Oc .Sh DESCRIPTION The .Nm swapon , swapoff and .Nm swapctl utilities are used to control swap devices in the system. At boot time all swap entries in .Pa /etc/fstab are added automatically when the system goes multi-user. Swap devices use a fixed interleave; the maximum number of devices is unlimited. There is no priority mechanism. .Pp The .Nm swapon utility adds the specified swap devices to the system. If the .Fl a option is used, all swap devices in .Pa /etc/fstab will be added, unless their .Dq noauto or .Dq late option is also set. If the .Fl L option is specified, swap devices with the .Dq late option will be added as well as ones with no option. If the .Fl q option is used, informational messages will not be written to standard output when a swap device is added. The .Fl E option causes each of following devices to receive a .Dv BIO_DELETE command. This command marks the device's blocks as unused, except those that might store a disk label. This marking can erase a crash dump. To delay .Nm swapon for a device until after .Nm savecore has copied the crash dump to another location, use the .Dq late option. .Pp The .Nm swapoff utility removes the specified swap devices from the system. If the .Fl a option is used, all swap devices in .Pa /etc/fstab will be removed, unless their .Dq noauto option is also set. If the .Fl L option is specified, only swap devices with the .Dq late option will be removed. If the .Fl q option is used, informational messages will not be written to standard output when a swap device is removed. Note that .Nm swapoff will fail and refuse to remove a swap device if there is insufficient VM (memory + remaining swap devices) to run the system. The .Nm swapoff utility must move swapped pages out of the device being removed which could lead to high system loads for a period of time, depending on how much data has been swapped out to that device. .Pp Other options supported by both .Nm swapon and .Nm swapoff are as follows: .Bl -tag -width indent .It Fl F Ar fstab Specify the .Pa fstab file to use (in conjunction with .Fl a Ns ). .El .Pp The .Nm swapctl utility exists primarily for those familiar with other .Bx Ns s and may be used to add, remove, or list swap devices. Note that the .Fl a option is used differently in .Nm swapctl and indicates that a specific list of devices should be added. The .Fl d option indicates that a specific list should be removed. The .Fl A and .Fl U options to .Nm swapctl operate on all swap entries in .Pa /etc/fstab which do not have their .Dq noauto option set. .Pp Swap information can be generated using the .Xr swapinfo 8 utility, .Nm pstat .Fl s , or .Nm swapctl .Fl l . The .Nm swapctl utility has the following options for listing swap: .Bl -tag -width indent .It Fl h Output values in human-readable form. .It Fl g Output values in gigabytes. .It Fl k Output values in kilobytes. .It Fl m Output values in megabytes. .It Fl l List the devices making up system swap. .It Fl s Print a summary line for system swap. .Pp The .Ev BLOCKSIZE environment variable is used if not specifically overridden. 512 byte blocks are used by default. .El .Sh FILES .Bl -tag -width ".Pa /dev/{ada,da}?s?b" -compact .It Pa /dev/{ada,da}?s?b standard paging devices .It Pa /dev/md? memory disk devices .It Pa /etc/fstab .Tn ASCII file system description table .El .Sh DIAGNOSTICS These utilities may fail for the reasons described in .Xr swapon 2 . .Sh SEE ALSO .Xr swapon 2 , .Xr fstab 5 , .Xr init 8 , .Xr mdconfig 8 , .Xr pstat 8 , .Xr rc 8 .Sh HISTORY The .Nm swapon utility appeared in .Bx 4.0 . The .Nm swapoff and .Nm swapctl utilities appeared in .Fx 5.1 .
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