1SWAPON(8) System Administration SWAPON(8)
2
6 swapon, swapoff - enable/disable devices and files for paging and
7 swapping
8
10 swapon [options] [specialfile...]
11 swapoff [-va] [specialfile...]
13
15 swapon is used to specify devices on which paging and swapping are to
16 take place.
17 The device or file used is given by the specialfile parameter. It may
19 be of the form -L label or -U uuid to indicate a device by label or
20 uuid.
21 Calls to swapon normally occur in the system boot scripts making all
23 swap devices available, so that the paging and swapping activity is
24 interleaved across several devices and files.
25 swapoff disables swapping on the specified devices and files. When the
27 -a flag is given, swapping is disabled on all known swap devices and
28 files (as found in /proc/swaps or /etc/fstab).
29
31 -a, --all
32 All devices marked as "swap" in /etc/fstab are made available,
33 except for those with the "noauto" option. Devices that are already
34 being used as swap are silently skipped.
35 -T, --fstab path
37 Specifies an alternative fstab file for compatibility with
38 mount(8). If path is a directory, then the files in the directory
39 are sorted by strverscmp(3); files that start with "." or without
40 an .fstab extension are ignored. The option can be specified more
41 than once. This option is mostly designed for initramfs or chroot
42 scripts where additional configuration is specified beyond standard
43 system configuration.
44 -d, --discard[=policy]
46 Enable swap discards, if the swap backing device supports the
47 discard or trim operation. This may improve performance on some
48 Solid State Devices, but often it does not. The option allows one
49 to select between two available swap discard policies:
50 --discard=once
52 to perform a single-time discard operation for the whole swap
53 area at swapon; or
54 --discard=pages
56 to asynchronously discard freed swap pages before they are
57 available for reuse.
58 If no policy is selected, the default behavior is to enable both
60 discard types. The /etc/fstab mount options discard, discard=once,
61 or discard=pages may also be used to enable discard flags.
62 -e, --ifexists
64 Silently skip devices that do not exist. The /etc/fstab mount
65 option nofail may also be used to skip non-existing device.
66 -f, --fixpgsz
68 Reinitialize (exec mkswap) the swap space if its page size does not
69 match that of the current running kernel. mkswap(8) initializes the
70 whole device and does not check for bad blocks.
71 -L label
73 Use the partition that has the specified label. (For this, access
74 to /proc/partitions is needed.)
75 -o, --options opts
77 Specify swap options by an fstab-compatible comma-separated string.
78 For example:
79 swapon -o pri=1,discard=pages,nofail /dev/sda2
81 The opts string is evaluated last and overrides all other command
83 line options.
84 -p, --priority priority
86 Specify the priority of the swap device. priority is a value
87 between -1 and 32767. Higher numbers indicate higher priority. See
88 swapon(2) for a full description of swap priorities. Add pri=value
89 to the option field of /etc/fstab for use with swapon -a. When no
90 priority is defined, it defaults to -1.
91 -s, --summary
93 Display swap usage summary by device. Equivalent to cat
94 /proc/swaps. This output format is DEPRECATED in favour of --show
95 that provides better control on output data.
96 --show[=column...]
98 Display a definable table of swap areas. See the --help output for
99 a list of available columns.
100 --output-all
102 Output all available columns.
103 --noheadings
105 Do not print headings when displaying --show output.
106 --raw
108 Display --show output without aligning table columns.
109 --bytes
111 Display swap size in bytes in --show output instead of in
112 user-friendly units.
113 -U uuid
115 Use the partition that has the specified uuid.
116 -v, --verbose
118 Be verbose.
119 -h, --help
121 Display help text and exit.
122 -V, --version
124 Print version and exit.
125
127 swapoff has the following exit status values since v2.36:
128 0
130 success
131 2
133 system has insufficient memory to stop swapping (OOM)
134 4
136 swapoff(2) syscall failed for another reason
137 8
139 non-swapoff(2) syscall system error (out of memory, ...)
140 16
142 usage or syntax error
143 32
145 all swapoff failed on --all
146 64
148 some swapoff succeeded on --all
149 The command swapoff --all returns 0 (all succeeded), 32 (all failed),
151 or 64 (some failed, some succeeded).
152 + The old versions before v2.36 has no documented exit status, 0 means
154 success in all versions.
155
157 LIBMOUNT_DEBUG=all
158 enables libmount debug output.
159 LIBBLKID_DEBUG=all
161 enables libblkid debug output.
162
164 /dev/sd??
165 standard paging devices
166 /etc/fstab
168 ascii filesystem description table
169
171 Files with holes
172 The swap file implementation in the kernel expects to be able to write
173 to the file directly, without the assistance of the filesystem. This is
174 a problem on files with holes or on copy-on-write files on filesystems
175 like Btrfs.
176 Commands like cp(1) or truncate(1) create files with holes. These files
178 will be rejected by swapon.
179 Preallocated files created by fallocate(1) may be interpreted as files
181 with holes too depending of the filesystem. Preallocated swap files are
182 supported on XFS since Linux 4.18.
183 The most portable solution to create a swap file is to use dd(1) and
185 /dev/zero.
186 Btrfs
188 Swap files on Btrfs are supported since Linux 5.0 on files with nocow
189 attribute. See the btrfs(5) manual page for more details.
190 NFS
192 Swap over NFS may not work.
193 Suspend
195 swapon automatically detects and rewrites a swap space signature with
196 old software suspend data (e.g., S1SUSPEND, S2SUSPEND, ...). The
197 problem is that if we don’t do it, then we get data corruption the next
198 time an attempt at unsuspending is made.
199
201 The swapon command appeared in 4.0BSD.
202
204 swapoff(2), swapon(2), fstab(5), init(8), fallocate(1), mkswap(8),
205 mount(8), rc(8)
206
208 For bug reports, use the issue tracker at
209 https://github.com/util-linux/util-linux/issues.
210
212 The swapon command is part of the util-linux package which can be
213 downloaded from Linux Kernel Archive
214 <https://www.kernel.org/pub/linux/utils/util-linux/>.
215util-linux 2.39.2 2023-08-17 SWAPON(8)