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1 | <?xml version="1.0"?> |
2 | <!--*-nxml-*--> | |
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3 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
4 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
db9ecf05 | 5 | <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> |
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6 | <refentry id="systemd.preset"> |
7 | ||
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8 | <refentryinfo> |
9 | <title>systemd.preset</title> | |
10 | <productname>systemd</productname> | |
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11 | </refentryinfo> |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>systemd.preset</refentrytitle> | |
15 | <manvolnum>5</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>systemd.preset</refname> | |
20 | <refpurpose>Service enablement presets</refpurpose> | |
21 | </refnamediv> | |
22 | ||
23 | <refsynopsisdiv> | |
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24 | <para><simplelist> |
25 | <member><filename>/etc/systemd/system-preset/*.preset</filename></member> | |
26 | <member><filename>/run/systemd/system-preset/*.preset</filename></member> | |
27 | <member><filename>/usr/lib/systemd/system-preset/*.preset</filename></member> | |
28 | <member><filename>/etc/systemd/user-preset/*.preset</filename></member> | |
29 | <member><filename>/run/systemd/user-preset/*.preset</filename></member> | |
30 | <member><filename>/usr/lib/systemd/user-preset/*.preset</filename></member> | |
31 | </simplelist></para> | |
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32 | </refsynopsisdiv> |
33 | ||
34 | <refsect1> | |
35 | <title>Description</title> | |
36 | ||
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37 | <para>Preset files may be used to encode policy which units shall be enabled by default and which ones |
38 | shall be disabled. They are read by <command>systemctl preset</command> which uses this information to | |
39 | enable or disable a unit. Depending on that policy, <command>systemctl preset</command> is identical to | |
40 | <command>systemctl enable</command> or <command>systemctl disable</command>. | |
41 | ||
42 | <command>systemctl preset</command> is used by the post install scriptlets of rpm packages (or other OS | |
43 | package formats), to enable/disable specific units by default on package installation, enforcing | |
44 | distribution, spin or administrator preset policy. This allows choosing a certain set of units to be | |
45 | enabled/disabled even before installing the actual package. For more information, see | |
46 | <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para> | |
47 | ||
48 | <para>It is not recommended to ship preset files within the respective software packages implementing the | |
49 | units, but rather centralize them in a distribution or spin default policy, which can be amended by | |
50 | administrator policy, see below.</para> | |
798d3a52 | 51 | |
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52 | <para>If no preset files exist, preset operations will enable all units that are installed by default. If |
53 | this is not desired and all units shall rather be disabled, it is necessary to ship a preset file with a | |
54 | single, catchall "<filename>disable *</filename>" line. (See example 1, below.)</para> | |
55 | ||
56 | <para>When the machine is booted for the first time, | |
57 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will | |
58 | enable/disable all units according to preset policy, similarly to <command>systemctl | |
59 | preset-all</command>. Also see "First Boot Semantics" in | |
60 | <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>. | |
61 | </para> | |
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62 | </refsect1> |
63 | ||
64 | <refsect1> | |
65 | <title>Preset File Format</title> | |
66 | ||
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67 | <para>The preset files contain a list of directives, one per line. Empty lines and lines whose first |
68 | non-whitespace character is <literal>#</literal> or <literal>;</literal> are ignored. Each directive | |
69 | consists of one of the words <literal>enable</literal>, <literal>disable</literal>, or | |
70 | <literal>ignore</literal>, followed by whitespace and a unit name. The unit name may contain shell-style | |
71 | wildcards.</para> | |
72 | ||
73 | <para>For the enable directive for template units, one or more instance names may be specified as a | |
74 | space-separated list after the unit name. In this case, those instances will be enabled instead of the | |
75 | instance specified via DefaultInstance= in the unit.</para> | |
798d3a52 | 76 | |
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77 | <para>Presets must refer to the "real" unit file, and not to any aliases. See |
78 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
79 | for a description of unit aliasing.</para> | |
80 | ||
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81 | <para>Three different directives are understood: <literal>enable</literal> may be used to enable units by |
82 | default, <literal>disable</literal> to disable units by default, and <literal>ignore</literal> to ignore | |
83 | units and leave existing configuration intact.</para> | |
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84 | |
85 | <para>If multiple lines apply to a unit name, the first matching | |
86 | one takes precedence over all others.</para> | |
87 | ||
88 | <para>Each preset file shall be named in the style of | |
9e0d90f9 | 89 | <filename><priority>-<policy-name>.preset</filename>. Files |
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90 | in <filename>/etc/</filename> override files with the same name in |
91 | <filename>/usr/lib/</filename> and <filename>/run/</filename>. | |
92 | Files in <filename>/run/</filename> override files with the same | |
93 | name in <filename>/usr/lib/</filename>. Packages should install | |
94 | their preset files in <filename>/usr/lib/</filename>. Files in | |
95 | <filename>/etc/</filename> are reserved for the local | |
96 | administrator, who may use this logic to override the preset files | |
97 | installed by vendor packages. All preset files are sorted by their | |
98 | filename in lexicographic order, regardless of which of the | |
99 | directories they reside in. If multiple files specify the same | |
100 | unit name, the entry in the file with the lexicographically | |
101 | earliest name will be applied. It is recommended to prefix all | |
102 | filenames with a two-digit number and a dash, to simplify the | |
103 | ordering of the files.</para> | |
104 | ||
105 | <para>If the administrator wants to disable a preset file supplied | |
106 | by the vendor, the recommended way is to place a symlink to | |
107 | <filename>/dev/null</filename> in | |
12b42c76 | 108 | <filename>/etc/systemd/system-preset/</filename> bearing the same |
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109 | filename.</para> |
110 | </refsect1> | |
111 | ||
112 | <refsect1> | |
1655cdee | 113 | <title>Examples</title> |
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114 | |
115 | <example> | |
1655cdee | 116 | <title>Default to off</title> |
798d3a52 | 117 | |
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118 | <programlisting># /usr/lib/systemd/system-preset/99-default.preset |
119 | ||
120 | disable *</programlisting> | |
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121 | </example> |
122 | ||
123 | <para>This disables all units. Due to the filename prefix | |
124 | <literal>99-</literal>, it will be read last and hence can easily | |
1655cdee | 125 | be overridden by spin or administrator preset policy.</para> |
798d3a52 | 126 | |
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127 | <example> |
128 | <title>Enable multiple template instances</title> | |
129 | ||
130 | <programlisting># /usr/lib/systemd/system-preset/80-dirsrv.preset | |
131 | ||
132 | enable dirsrv@.service foo bar baz</programlisting> | |
133 | </example> | |
134 | ||
135 | <para>This enables all three of <filename>dirsrv@foo.service</filename>, | |
136 | <filename>dirsrv@bar.service</filename> and <filename>dirsrv@baz.service</filename>.</para> | |
137 | ||
798d3a52 | 138 | <example> |
1655cdee | 139 | <title>A GNOME spin</title> |
798d3a52 | 140 | |
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141 | <programlisting># /usr/lib/systemd/system-preset/50-gnome.preset |
142 | ||
143 | enable gdm.service | |
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144 | enable colord.service |
145 | enable accounts-daemon.service | |
146 | enable avahi-daemon.*</programlisting> | |
147 | ||
798d3a52 | 148 | </example> |
75d67e68 | 149 | |
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150 | <para>This enables the three mentioned units, plus all |
151 | <filename>avahi-daemon</filename> regardless of which unit type. A | |
152 | file like this could be useful for inclusion in a GNOME spin of a | |
153 | distribution. It will ensure that the units necessary for GNOME | |
154 | are properly enabled as they are installed. It leaves all other | |
155 | units untouched, and subject to other (later) preset files, for | |
156 | example like the one from the first example above.</para> | |
75d67e68 | 157 | |
798d3a52 | 158 | <example> |
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159 | <title>Administrator policy</title> |
160 | ||
161 | <programlisting># /etc/systemd/system-preset/00-lennart.preset | |
75d67e68 | 162 | |
1655cdee | 163 | enable httpd.service |
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164 | enable sshd.service |
165 | enable postfix.service | |
166 | disable *</programlisting> | |
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167 | </example> |
168 | ||
169 | <para>This enables three specific services and disables all | |
170 | others. This is useful for administrators to specifically select | |
171 | the units to enable, and disable all others. Due to the filename | |
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172 | prefix <literal>00-</literal> it will be read early and |
173 | override all other preset policy files.</para> | |
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174 | </refsect1> |
175 | ||
7e215af7 | 176 | <refsect1> |
7bac23e8 | 177 | <title>Motivation for the preset logic</title> |
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178 | |
179 | <para>Different distributions have different policies on which services shall be enabled by default when | |
180 | the package they are shipped in is installed. On Fedora all services stay off by default, so that | |
181 | installing a package will not cause a service to be enabled (with some exceptions). On Debian all | |
182 | services are immediately enabled by default, so that installing a package will cause its services to be | |
183 | enabled right-away.</para> | |
184 | ||
185 | <para>Even within a single distribution, different spins (flavours, remixes, whatever you might want to | |
186 | call them) of a distribution also have different policies on what services to enable, and what services | |
187 | to leave off. For example, Fedora Workstation will enable <command>gdm</command> as display manager by | |
188 | default, while the Fedora KDE spin will enable <command>sddm</command> instead.</para> | |
189 | ||
190 | <para>Different sites might also have different policies what to turn on by default and what to turn | |
191 | off. For example, one administrator would prefer to enforce the policy of "<command>sshd</command> should | |
192 | be always on, but everything else off", while another one might say "<command>snmpd</command> always on, | |
193 | and for everything else use the distribution policy defaults".</para> | |
194 | ||
195 | <para>Traditionally, policy about which services shall be enabled were implemented in each package | |
196 | individually. This made it cumbersome to implement different policies per spin or per site, or to create | |
197 | software packages that do the right thing on more than one distribution. The enablement mechanism was | |
198 | also encoding the enablement policy.</para> | |
199 | ||
200 | <para>The preset mechanism allows clean separation of the enablement mechanism (inside the package | |
201 | scriptlets, by invoking <command>systemctl preset</command>) and enablement policy (centralized in the | |
202 | preset files), and lifts the configuration out of individual packages. Preset files may be written for | |
203 | specific distributions, for specific spins or for specific sites, in order to enforce different policies | |
204 | as needed. It is recommended to apply the policy encoded in preset files in package installation | |
205 | scriptlets.</para> | |
206 | </refsect1> | |
207 | ||
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208 | <refsect1> |
209 | <title>See Also</title> | |
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210 | <para><simplelist type="inline"> |
211 | <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member> | |
212 | <member><citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member> | |
213 | <member><citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry></member> | |
214 | </simplelist></para> | |
7e215af7 | 215 | |
be0d27ee | 216 | <para><citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
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217 | has a discussion of packaging scriptlets.</para> |
218 | ||
219 | <para>Fedora page introducing the use of presets: | |
220 | <ulink url="https://fedoraproject.org/wiki/Features/PackagePresets">Features/PackagePresets</ulink>. | |
221 | </para> | |
798d3a52 | 222 | </refsect1> |
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223 | |
224 | </refentry> |