xref: /freebsd/sbin/swapon/swapon.8 (revision a0b9e2e854027e6ff61fb075a1309dbc71c42b54)
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28.\"     @(#)swapon.8	8.1 (Berkeley) 6/5/93
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31.Dd May 19, 2020
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 (in conjunction with
147.Fl a Ns ).
148.El
149.Pp
150The
151.Nm swapctl
152utility exists primarily for those familiar with other
153.Bx Ns s
154and may be
155used to add, remove, or list swap devices.
156Note that the
157.Fl a
158option is used differently in
159.Nm swapctl
160and indicates that a specific list of devices should be added.
161The
162.Fl d
163option indicates that a specific list should be removed.
164The
165.Fl A
166and
167.Fl U
168options to
169.Nm swapctl
170operate on all swap entries in
171.Pa /etc/fstab
172which do not have their
173.Dq noauto
174option set.
175.Pp
176Swap information can be generated using the
177.Xr swapinfo 8
178utility,
179.Nm pstat
180.Fl s ,
181or
182.Nm swapctl
183.Fl l .
184The
185.Nm swapctl
186utility has the following options for listing swap:
187.Bl -tag -width indent
188.It Fl h
189Output values in human-readable form.
190.It Fl g
191Output values in gigabytes.
192.It Fl k
193Output values in kilobytes.
194.It Fl m
195Output values in megabytes.
196.It Fl l
197List the devices making up system swap.
198.It Fl s
199Print a summary line for system swap.
200.Pp
201The
202.Ev BLOCKSIZE
203environment variable is used if not specifically
204overridden.
205512 byte blocks are used by default.
206.El
207.Sh FILES
208.Bl -tag -width ".Pa /dev/{ada,da}?s?b" -compact
209.It Pa /dev/{ada,da}?s?b
210standard paging devices
211.It Pa /dev/md?
212memory disk devices
213.It Pa /etc/fstab
214.Tn ASCII
215file system description table
216.El
217.Sh DIAGNOSTICS
218These utilities may fail for the reasons described in
219.Xr swapon 2 .
220.Sh SEE ALSO
221.Xr swapon 2 ,
222.Xr fstab 5 ,
223.Xr init 8 ,
224.Xr mdconfig 8 ,
225.Xr pstat 8 ,
226.Xr rc 8
227.Sh HISTORY
228The
229.Nm swapon
230utility appeared in
231.Bx 4.0 .
232The
233.Nm swapoff
234and
235.Nm swapctl
236utilities appeared in
237.Fx 5.1 .
238