1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)swapon.8 8.1 (Berkeley) 6/5/93 29.\" $FreeBSD$ 30.\" 31.Dd June 21, 2019 32.Dt SWAPON 8 33.Os 34.Sh NAME 35.Nm swapon , swapoff , swapctl 36.Nd "specify devices for paging and swapping" 37.Sh SYNOPSIS 38.Nm swapon 39.Oo Fl F Ar fstab 40.Oc 41.Fl aLq | E Ar 42.Nm swapoff 43.Oo Fl F Ar fstab 44.Oc 45.Fl aLq | Ar 46.Nm swapctl 47.Op Fl AghklmsU 48.Oo 49.Fl a Ar 50| 51.Fl d Ar 52.Oc 53.Sh DESCRIPTION 54The 55.Nm swapon , swapoff 56and 57.Nm swapctl 58utilities are used to control swap devices in the system. 59At boot time all swap entries in 60.Pa /etc/fstab 61are added automatically when the system goes multi-user. 62Swap devices use a fixed interleave; the maximum number of devices 63is unlimited. 64There is no priority mechanism. 65.Pp 66The 67.Nm swapon 68utility adds the specified swap devices to the system. 69If the 70.Fl a 71option is used, all swap devices in 72.Pa /etc/fstab 73will be added, unless their 74.Dq noauto 75or 76.Dq late 77option is also set. 78If the 79.Fl L 80option is specified, 81swap devices with the 82.Dq late 83option will be added as well as ones with no option. 84If the 85.Fl q 86option is used, 87informational messages will not be 88written to standard output when a swap device is added. 89The 90.Fl E 91option causes each of following devices to receive a 92.Dv BIO_DELETE 93command. 94This command marks the device's blocks as unused, except those that 95might store a disk label. 96This marking can erase a crash dump. 97To delay 98.Nm swapon 99for a device until after 100.Nm savecore 101has copied the crash dump to another location, use the 102.Dq late 103option. 104.Pp 105The 106.Nm swapoff 107utility removes the specified swap devices from the system. 108If the 109.Fl a 110option is used, all swap devices in 111.Pa /etc/fstab 112will be removed, unless their 113.Dq noauto 114option is also set. 115If the 116.Fl L 117option is specified, 118only swap devices with the 119.Dq late 120option will be removed. 121If the 122.Fl q 123option is used, 124informational messages will not be 125written to standard output when a swap device is removed. 126Note that 127.Nm swapoff 128will fail and refuse to remove a swap device if there is insufficient 129VM (memory + remaining swap devices) to run the system. 130The 131.Nm swapoff 132utility 133must move swapped pages out of the device being removed which could 134lead to high system loads for a period of time, depending on how 135much data has been swapped out to that device. 136.Pp 137Other options supported by both 138.Nm swapon 139and 140.Nm swapoff 141are as follows: 142.Bl -tag -width indent 143.It Fl F Ar fstab 144Specify the 145.Pa fstab 146file to use. 147.El 148.Pp 149The 150.Nm swapctl 151utility exists primarily for those familiar with other 152.Bx Ns s 153and may be 154used to add, remove, or list swap devices. 155Note that the 156.Fl a 157option is used differently in 158.Nm swapctl 159and indicates that a specific list of devices should be added. 160The 161.Fl d 162option indicates that a specific list should be removed. 163The 164.Fl A 165and 166.Fl U 167options to 168.Nm swapctl 169operate on all swap entries in 170.Pa /etc/fstab 171which do not have their 172.Dq noauto 173option set. 174.Pp 175Swap information can be generated using the 176.Xr swapinfo 8 177utility, 178.Nm pstat 179.Fl s , 180or 181.Nm swapctl 182.Fl l . 183The 184.Nm swapctl 185utility has the following options for listing swap: 186.Bl -tag -width indent 187.It Fl h 188Output values in human-readable form. 189.It Fl g 190Output values in gigabytes. 191.It Fl k 192Output values in kilobytes. 193.It Fl m 194Output values in megabytes. 195.It Fl l 196List the devices making up system swap. 197.It Fl s 198Print a summary line for system swap. 199.Pp 200The 201.Ev BLOCKSIZE 202environment variable is used if not specifically 203overridden. 204512 byte blocks are used by default. 205.El 206.Sh FILES 207.Bl -tag -width ".Pa /dev/{ada,da}?s?b" -compact 208.It Pa /dev/{ada,da}?s?b 209standard paging devices 210.It Pa /dev/md? 211memory disk devices 212.It Pa /etc/fstab 213.Tn ASCII 214file system description table 215.El 216.Sh DIAGNOSTICS 217These utilities may fail for the reasons described in 218.Xr swapon 2 . 219.Sh SEE ALSO 220.Xr swapon 2 , 221.Xr fstab 5 , 222.Xr init 8 , 223.Xr mdconfig 8 , 224.Xr pstat 8 , 225.Xr rc 8 226.Sh HISTORY 227The 228.Nm swapon 229utility appeared in 230.Bx 4.0 . 231The 232.Nm swapoff 233and 234.Nm swapctl 235utilities appeared in 236.Fx 5.1 . 237