xref: /freebsd/sbin/swapon/swapon.8 (revision 640235e2c2ba32947f7c59d168437ffa1280f1e6)
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28.\"     @(#)swapon.8	8.1 (Berkeley) 6/5/93
29.\" $FreeBSD$
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31.Dd November 22, 2013
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 | 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.
89.Pp
90The
91.Nm swapoff
92utility removes the specified swap devices from the system.
93If the
94.Fl a
95option is used, all swap devices in
96.Pa /etc/fstab
97will be removed, unless their
98.Dq noauto
99or
100.Dq late
101option is also set.
102If the
103.Fl L
104option is specified,
105swap devices with the
106.Dq late
107option will be removed as well as ones with no option.
108If the
109.Fl q
110option is used,
111informational messages will not be
112written to standard output when a swap device is removed.
113Note that
114.Nm swapoff
115will fail and refuse to remove a swap device if there is insufficient
116VM (memory + remaining swap devices) to run the system.
117The
118.Nm swapoff
119utility
120must move swapped pages out of the device being removed which could
121lead to high system loads for a period of time, depending on how
122much data has been swapped out to that device.
123.Pp
124Other options supported by both
125.Nm swapon
126and
127.Nm swapoff
128are as follows:
129.Bl -tag -width indent
130.It Fl F Ar fstab
131Specify the
132.Pa fstab
133file to use.
134.El
135.Pp
136The
137.Nm swapctl
138utility exists primarily for those familiar with other
139.Bx Ns s
140and may be
141used to add, remove, or list swap devices.
142Note that the
143.Fl a
144option is used differently in
145.Nm swapctl
146and indicates that a specific list of devices should be added.
147The
148.Fl d
149option indicates that a specific list should be removed.
150The
151.Fl A
152and
153.Fl U
154options to
155.Nm swapctl
156operate on all swap entries in
157.Pa /etc/fstab
158which do not have their
159.Dq noauto
160option set.
161.Pp
162Swap information can be generated using the
163.Xr swapinfo 8
164utility,
165.Nm pstat
166.Fl s ,
167or
168.Nm swapctl
169.Fl l .
170The
171.Nm swapctl
172utility has the following options for listing swap:
173.Bl -tag -width indent
174.It Fl h
175Output values in human-readable form.
176.It Fl g
177Output values in gigabytes.
178.It Fl k
179Output values in kilobytes.
180.It Fl m
181Output values in megabytes.
182.It Fl l
183List the devices making up system swap.
184.It Fl s
185Print a summary line for system swap.
186.Pp
187The
188.Ev BLOCKSIZE
189environment variable is used if not specifically
190overridden.
191512 byte blocks are used by default.
192.El
193.Sh FILES
194.Bl -tag -width ".Pa /dev/{ada,da}?s?b" -compact
195.It Pa /dev/{ada,da}?s?b
196standard paging devices
197.It Pa /dev/md?
198memory disk devices
199.It Pa /etc/fstab
200.Tn ASCII
201file system description table
202.El
203.Sh DIAGNOSTICS
204These utilities may fail for the reasons described in
205.Xr swapon 2 .
206.Sh SEE ALSO
207.Xr swapon 2 ,
208.Xr fstab 5 ,
209.Xr init 8 ,
210.Xr mdconfig 8 ,
211.Xr pstat 8 ,
212.Xr rc 8
213.Sh HISTORY
214The
215.Nm swapon
216utility appeared in
217.Bx 4.0 .
218The
219.Nm swapoff
220and
221.Nm swapctl
222utilities appeared in
223.Fx 5.1 .
224