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.Dd November 29, 2021 29.Dt SWAPON 8 30.Os 31.Sh NAME 32.Nm swapon , swapoff , swapctl 33.Nd "specify devices for paging and swapping" 34.Sh SYNOPSIS 35.Nm swapon 36.Oo Fl F Ar fstab 37.Oc 38.Fl aLq | E Ar 39.Nm swapoff 40.Oo Fl F Ar fstab 41.Oc 42.Fl afLq | Ar 43.Nm swapctl 44.Op Fl AfghklmsU 45.Oo 46.Fl a Ar 47| 48.Fl d Ar 49.Oc 50.Sh DESCRIPTION 51The 52.Nm swapon , swapoff 53and 54.Nm swapctl 55utilities are used to control swap devices in the system. 56At boot time all swap entries in 57.Pa /etc/fstab 58are added automatically when the system goes multi-user. 59Swap devices use a fixed interleave; the maximum number of devices 60is unlimited. 61There is no priority mechanism. 62.Pp 63The 64.Nm swapon 65utility adds the specified swap devices to the system. 66If the 67.Fl a 68option is used, all swap devices in 69.Pa /etc/fstab 70will be added, unless their 71.Dq noauto 72or 73.Dq late 74option is also set. 75If the 76.Fl L 77option is specified, 78swap devices with the 79.Dq late 80option will be added as well as ones with no option. 81If the 82.Fl q 83option is used, 84informational messages will not be 85written to standard output when a swap device is added. 86The 87.Fl E 88option causes each of following devices to receive a 89.Dv BIO_DELETE 90command. 91This command marks the device's blocks as unused, except those that 92might store a disk label. 93This marking can erase a crash dump. 94To delay 95.Nm swapon 96for a device until after 97.Nm savecore 98has copied the crash dump to another location, use the 99.Dq late 100option. 101.Pp 102The 103.Nm swapoff 104utility removes the specified swap devices from the system. 105If the 106.Fl a 107option is used, all swap devices in 108.Pa /etc/fstab 109will be removed, unless their 110.Dq noauto 111option is also set. 112If the 113.Fl L 114option is specified, 115only swap devices with the 116.Dq late 117option will be removed. 118If the 119.Fl q 120option is used, 121informational messages will not be 122written to standard output when a swap device is removed. 123Note that 124.Nm swapoff 125will fail and refuse to remove a swap device if a very conservative 126check does not conclude that there is sufficient VM (memory + 127remaining swap devices) to run the system. 128The 129.Fl f 130option turns off this check, which could deadlock the system 131if there is insufficient swap space remaining. 132.Pp 133The 134.Nm swapoff 135utility 136must move swapped pages out of the device being removed which could 137lead to high system loads for a period of time, depending on how 138much data has been swapped out to that device. 139.Pp 140Other options supported by both 141.Nm swapon 142and 143.Nm swapoff 144are as follows: 145.Bl -tag -width indent 146.It Fl F Ar fstab 147Specify the 148.Pa fstab 149file to use (in conjunction with 150.Fl a Ns ). 151.El 152.Pp 153The 154.Nm swapctl 155utility exists primarily for those familiar with other 156.Bx Ns s 157and may be 158used to add, remove, or list swap devices. 159Note that the 160.Fl a 161option is used differently in 162.Nm swapctl 163and indicates that a specific list of devices should be added. 164The 165.Fl d 166option indicates that a specific list should be removed. 167The 168.Fl A 169and 170.Fl U 171options to 172.Nm swapctl 173operate on all swap entries in 174.Pa /etc/fstab 175which do not have their 176.Dq noauto 177option set. 178.Pp 179Swap information can be generated using the 180.Xr swapinfo 8 181utility, 182.Nm pstat 183.Fl s , 184or 185.Nm swapctl 186.Fl l . 187The 188.Nm swapctl 189utility has the following options for listing swap: 190.Bl -tag -width indent 191.It Fl h 192Output values in human-readable form. 193.It Fl g 194Output values in gigabytes. 195.It Fl k 196Output values in kilobytes. 197.It Fl m 198Output values in megabytes. 199.It Fl l 200List the devices making up system swap. 201.It Fl s 202Print a summary line for system swap. 203.Pp 204The 205.Ev BLOCKSIZE 206environment variable is used if not specifically 207overridden. 208512 byte blocks are used by default. 209.El 210.Sh FILES 211.Bl -tag -width ".Pa /dev/{ada,da}?s?b" -compact 212.It Pa /dev/{ada,da}?s?b 213standard paging devices 214.It Pa /dev/md? 215memory disk devices 216.It Pa /etc/fstab 217.Tn ASCII 218file system description table 219.El 220.Sh DIAGNOSTICS 221These utilities may fail for the reasons described in 222.Xr swapon 2 . 223.Sh SEE ALSO 224.Xr swapon 2 , 225.Xr fstab 5 , 226.Xr init 8 , 227.Xr mdconfig 8 , 228.Xr pstat 8 , 229.Xr rc 8 230.Sh HISTORY 231The 232.Nm swapon 233utility appeared in 234.Bx 4.0 . 235The 236.Nm swapoff 237and 238.Nm swapctl 239utilities appeared in 240.Fx 5.1 . 241