1SYSTEMD.SWAP(5) systemd.swap SYSTEMD.SWAP(5)
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6 systemd.swap - Swap unit configuration
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9 swap.swap
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12 A unit configuration file whose name ends in ".swap" encodes
13 information about a swap device or file for memory paging controlled
14 and supervised by systemd.
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16 This man page lists the configuration options specific to this unit
17 type. See systemd.unit(5) for the common options of all unit
18 configuration files. The common configuration items are configured in
19 the generic [Unit] and [Install] sections. The swap specific
20 configuration options are configured in the [Swap] section.
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22 Additional options are listed in systemd.exec(5), which define the
23 execution environment the swapon(8) program is executed in, in
24 systemd.kill(5), which define the way these processes are terminated,
25 and in systemd.resource-control(5), which configure resource control
26 settings for these processes of the unit.
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28 Swap units must be named after the devices or files they control.
29 Example: the swap device /dev/sda5 must be configured in a unit file
30 dev-sda5.swap. For details about the escaping logic used to convert a
31 file system path to a unit name, see systemd.unit(5). Note that swap
32 units cannot be templated, nor is possible to add multiple names to a
33 swap unit by creating additional symlinks to it.
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35 Note that swap support on Linux is privileged, swap units are hence
36 only available in the system service manager (and root's user service
37 manager), but not in unprivileged user's service manager.
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40 Implicit Dependencies
41 The following dependencies are implicitly added:
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43 • All swap units automatically get the BindsTo= and After=
44 dependencies on the device units or the mount units of the files
45 they are activated from.
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47 Additional implicit dependencies may be added as result of execution
48 and resource control parameters as documented in systemd.exec(5) and
49 systemd.resource-control(5).
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51 Default Dependencies
52 The following dependencies are added unless DefaultDependencies=no is
53 set:
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55 • Swap units automatically acquire a Conflicts= and a Before=
56 dependency on umount.target so that they are deactivated at
57 shutdown as well as a Before=swap.target dependency.
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60 Swap units may either be configured via unit files, or via /etc/fstab
61 (see fstab(5) for details). Swaps listed in /etc/fstab will be
62 converted into native units dynamically at boot and when the
63 configuration of the system manager is reloaded. See systemd-fstab-
64 generator(8) for details about the conversion.
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66 If a swap device or file is configured in both /etc/fstab and a unit
67 file, the configuration in the latter takes precedence.
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69 When reading /etc/fstab, a few special options are understood by
70 systemd which influence how dependencies are created for swap units.
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72 noauto, auto
73 With noauto, the swap unit will not be added as a dependency for
74 swap.target. This means that it will not be activated automatically
75 during boot, unless it is pulled in by some other unit. The auto
76 option has the opposite meaning and is the default.
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78 nofail
79 With nofail, the swap unit will be only wanted, not required by
80 swap.target. This means that the boot will continue even if this
81 swap device is not activated successfully.
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83 x-systemd.device-timeout=
84 Configure how long systemd should wait for a device to show up
85 before giving up on an entry from /etc/fstab. Specify a time in
86 seconds or explicitly append a unit such as "s", "min", "h", "ms".
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88 Note that this option can only be used in /etc/fstab, and will be
89 ignored when part of the Options= setting in a unit file.
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91 x-systemd.makefs
92 The swap structure will be initialized on the device. If the device
93 is not "empty", i.e. it contains any signature, the operation will
94 be skipped. It is hence expected that this option remains set even
95 after the device has been initialized.
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97 Note that this option can only be used in /etc/fstab, and will be
98 ignored when part of the Options= setting in a unit file.
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100 See systemd-mkswap@.service(8) and the discussion of wipefs(8) in
101 systemd.mount(5).
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104 Swap unit files must include a [Swap] section, which carries
105 information about the swap device it supervises. A number of options
106 that may be used in this section are shared with other unit types.
107 These options are documented in systemd.exec(5) and systemd.kill(5).
108 The options specific to the [Swap] section of swap units are the
109 following:
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111 What=
112 Takes an absolute path of a device node or file to use for paging.
113 See swapon(8) for details. If this refers to a device node, a
114 dependency on the respective device unit is automatically created.
115 (See systemd.device(5) for more information.) If this refers to a
116 file, a dependency on the respective mount unit is automatically
117 created. (See systemd.mount(5) for more information.) This option
118 is mandatory. Note that the usual specifier expansion is applied to
119 this setting, literal percent characters should hence be written as
120 "%%".
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122 Priority=
123 Swap priority to use when activating the swap device or file. This
124 takes an integer. This setting is optional and ignored when the
125 priority is set by pri= in the Options= key.
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127 Options=
128 May contain an option string for the swap device. This may be used
129 for controlling discard options among other functionality, if the
130 swap backing device supports the discard or trim operation. (See
131 swapon(8) for more information.) Note that the usual specifier
132 expansion is applied to this setting, literal percent characters
133 should hence be written as "%%".
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135 TimeoutSec=
136 Configures the time to wait for the swapon command to finish. If a
137 command does not exit within the configured time, the swap will be
138 considered failed and be shut down again. All commands still
139 running will be terminated forcibly via SIGTERM, and after another
140 delay of this time with SIGKILL. (See KillMode= in
141 systemd.kill(5).) Takes a unit-less value in seconds, or a time
142 span value such as "5min 20s". Pass "0" to disable the timeout
143 logic. Defaults to DefaultTimeoutStartSec= from the manager
144 configuration file (see systemd-system.conf(5)).
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146 Check systemd.exec(5) and systemd.kill(5) for more settings.
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149 systemd(1), systemctl(1), systemd-system.conf(5), systemd.unit(5),
150 systemd.exec(5), systemd.kill(5), systemd.resource-control(5),
151 systemd.device(5), systemd.mount(5), swapon(8), systemd-fstab-
152 generator(8), systemd.directives(7)
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156systemd 248 SYSTEMD.SWAP(5)