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7<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
8
9<refentry id="systemd.syntax">
10
11  <refentryinfo>
12    <title>systemd.syntax</title>
13    <productname>systemd</productname>
14  </refentryinfo>
15
16  <refmeta>
17    <refentrytitle>systemd.syntax</refentrytitle>
18    <manvolnum>7</manvolnum>
19  </refmeta>
20
21  <refnamediv>
22    <refname>systemd.syntax</refname>
23    <refpurpose>General syntax of systemd configuration files</refpurpose>
24  </refnamediv>
25
26  <refsect1>
27    <title>Introduction</title>
28
29    <para>This page describes the basic principles of configuration files used by
30    <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
31    and related programs for:
32    <itemizedlist>
33      <listitem><para>systemd unit files, see
34      <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
35      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
36      <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
37      <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
38      <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
39      <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
40      <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
41      <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
42      <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
43      <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
44      <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
45      <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
46      <citerefentry><refentrytitle>systemd.nspawn</refentrytitle><manvolnum>5</manvolnum></citerefentry>
47      </para></listitem>
48
49      <listitem><para>link files, see
50      <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>
51      </para></listitem>
52
53      <listitem><para>netdev and network files, see
54      <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
55      <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
56      </para></listitem>
57
58      <listitem><para>daemon config files, see
59      <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
60      <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
61      <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
62      <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
63      <citerefentry><refentrytitle>journal-remote.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
64      <citerefentry><refentrytitle>journal-upload.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
65      <citerefentry><refentrytitle>systemd-sleep.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
66      <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
67      </para></listitem>
68    </itemizedlist>
69    </para>
70
71    <para>The syntax is inspired by
72    <ulink url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG Desktop Entry Specification</ulink>
73    <filename>.desktop</filename> files, which are in turn inspired by Microsoft Windows
74    <filename>.ini</filename> files.
75    </para>
76
77    <para>Each file is a plain text file divided into sections, with configuration entries in the style
78    <replaceable>key</replaceable>=<replaceable>value</replaceable>. Whitespace immediately before or after
79    the <literal>=</literal> is ignored. Empty lines and lines starting with <literal>#</literal> or
80    <literal>;</literal> are ignored, which may be used for commenting.</para>
81
82    <para>Lines ending in a backslash are concatenated with the following line while reading and the
83    backslash is replaced by a space character. This may be used to wrap long lines. The limit on
84    line length is very large (currently 1 MB), but it is recommended to avoid such long lines and
85    use multiple directives, variable substitution, or other mechanism as appropriate for the given
86    file type. When a comment line or lines follow a line ending with a backslash, the comment block
87    is ignored, so the continued line is concatenated with whatever follows the comment block.</para>
88
89    <example><programlisting>[Section A]
90KeyOne=value 1
91KeyTwo=value 2
92
93# a comment
94
95[Section B]
96Setting="something" "some thing" "…"
97KeyTwo=value 2 \
98       value 2 continued
99
100[Section C]
101KeyThree=value 3\
102# this line is ignored
103; this line is ignored too
104       value 3 continued
105</programlisting></example>
106
107    <para>Boolean arguments used in configuration files can be written in
108    various formats. For positive settings the strings
109    <option>1</option>, <option>yes</option>, <option>true</option>
110    and <option>on</option> are equivalent. For negative settings, the
111    strings <option>0</option>, <option>no</option>,
112    <option>false</option> and <option>off</option> are
113    equivalent.</para>
114
115    <para>Time span values encoded in configuration files can be written in various formats. A stand-alone
116    number specifies a time in seconds.  If suffixed with a time unit, the unit is honored. A
117    concatenation of multiple values with units is supported, in which case the values are added
118    up. Example: <literal>50</literal> refers to 50 seconds; <literal>2min 200ms</literal> refers to
119    2 minutes and 200 milliseconds, i.e. 120200 ms.  The following time units are understood:
120    <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, <literal>d</literal>,
121    <literal>w</literal>, <literal>ms</literal>, <literal>us</literal>.  For details see
122    <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
123
124    <para>Various settings are allowed to be specified more than once, in which case the
125    interpretation depends on the setting. Often, multiple settings form a list, and setting to an
126    empty value "resets", which means that previous assignments are ignored. When this is allowed,
127    it is mentioned in the description of the setting. Note that using multiple assignments to the
128    same value makes the file incompatible with parsers for the XDG <filename>.desktop</filename>
129    file format.</para>
130  </refsect1>
131
132  <refsect1>
133    <title>Quoting</title>
134
135    <para>For settings where quoting is allowed, the following general rules apply: double quotes ("…") and
136    single quotes ('…') may be used to wrap a whole item (the opening quote may appear only at the beginning
137    or after whitespace that is not quoted, and the closing quote must be followed by whitespace or the end
138    of line), in which case everything until the next matching quote becomes part of the same item. Quotes
139    themselves are removed. C-style escapes are supported. The table below contains the list of known escape
140    patterns. Only escape patterns which match the syntax in the table are allowed; other patterns may be
141    added in the future and unknown patterns will result in a warning. In particular, any backslashes should
142    be doubled. Finally, a trailing backslash (<literal>\</literal>) may be used to merge lines, as described
143    above. UTF-8 is accepted, and hence typical unicode characters do not need to be escaped.</para>
144
145    <table>
146      <title>Supported escapes</title>
147      <tgroup cols='2'>
148        <colspec colname='escape' />
149        <colspec colname='meaning' />
150        <thead>
151          <row>
152            <entry>Literal</entry>
153            <entry>Actual value</entry>
154          </row>
155        </thead>
156        <tbody>
157          <row>
158            <entry><literal>\a</literal></entry>
159            <entry>bell</entry>
160          </row>
161          <row>
162            <entry><literal>\b</literal></entry>
163            <entry>backspace</entry>
164          </row>
165          <row>
166            <entry><literal>\f</literal></entry>
167            <entry>form feed</entry>
168          </row>
169          <row>
170            <entry><literal>\n</literal></entry>
171            <entry>newline</entry>
172          </row>
173          <row>
174            <entry><literal>\r</literal></entry>
175            <entry>carriage return</entry>
176          </row>
177          <row>
178            <entry><literal>\t</literal></entry>
179            <entry>tab</entry>
180          </row>
181          <row>
182            <entry><literal>\v</literal></entry>
183            <entry>vertical tab</entry>
184          </row>
185          <row>
186            <entry><literal>\\</literal></entry>
187            <entry>backslash</entry>
188          </row>
189          <row>
190            <entry><literal>\"</literal></entry>
191            <entry>double quotation mark</entry>
192          </row>
193          <row>
194            <entry><literal>\'</literal></entry>
195            <entry>single quotation mark</entry>
196          </row>
197          <row>
198            <entry><literal>\s</literal></entry>
199            <entry>space</entry>
200          </row>
201          <row>
202            <entry><literal>\x<replaceable>xx</replaceable></literal></entry>
203            <entry>character number <replaceable>xx</replaceable> in hexadecimal encoding</entry>
204          </row>
205          <row>
206            <entry><literal>\<replaceable>nnn</replaceable></literal></entry>
207            <entry>character number <replaceable>nnn</replaceable> in octal encoding</entry>
208          </row>
209          <row>
210            <entry><literal>\u<replaceable>nnnn</replaceable></literal></entry>
211            <entry>unicode code point <replaceable>nnnn</replaceable> in hexadecimal encoding</entry>
212          </row>
213          <row>
214            <entry><literal>\U<replaceable>nnnnnnnn</replaceable></literal></entry>
215            <entry>unicode code point <replaceable>nnnnnnnn</replaceable> in hexadecimal encoding</entry>
216          </row>
217        </tbody>
218      </tgroup>
219    </table>
220  </refsect1>
221
222  <refsect1>
223    <title>See Also</title>
224    <para>
225      <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
226    </para>
227  </refsect1>
228
229</refentry>
230