man/systemd.syntax.xml

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   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></para></listitem>
  46
  47       <listitem><para>daemon config files, see
  48       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  49       <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  50       <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  51       <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  52       <citerefentry><refentrytitle>journal-remote.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  53       <citerefentry><refentrytitle>journal-upload.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  54       <citerefentry><refentrytitle>systemd-sleep.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  55       <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  56       </para></listitem>
  57     </itemizedlist>
  58     </para>
  59
  60     <para>The syntax is inspired by
  61     <ulink url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG Desktop Entry Specification</ulink>
  62     <filename>.desktop</filename> files, which are in turn inspired by Microsoft Windows
  63     <filename>.ini</filename> files.
  64     </para>
  65
  66     <para>Each file is a plain text file divided into sections, with configuration entries in the
  67     style <replaceable>key</replaceable>=<replaceable>value</replaceable>.
  68     Whitespace immediately before or after the <literal>=</literal> is ignored. Empty lines and lines starting with <literal>#</literal> or <literal>;</literal> are
  69     ignored, which may be used for commenting.</para>
  70
  71     <para>Lines ending in a backslash are concatenated with the following line while reading and the
  72     backslash is replaced by a space character. This may be used to wrap long lines. The limit on
  73     line length is very large (currently 1 MB), but it is recommended to avoid such long lines and
  74     use multiple directives, variable substitution, or other mechanism as appropriate for the given
  75     file type. When a comment line or lines follow a line ending with a backslash, the comment block
  76     is ignored, so the continued line is concatenated with whatever follows the comment block.</para>
  77
  78     <example><programlisting>[Section A]
  79 KeyOne=value 1
  80 KeyTwo=value 2
  81
  82 # a comment
  83
  84 [Section B]
  85 Setting="something" "some thing" "…"
  86 KeyTwo=value 2 \
  87        value 2 continued
  88
  89 [Section C]
  90 KeyThree=value 2\
  91 # this line is ignored
  92 ; this line is ignored too
  93        value 2 continued
  94 </programlisting></example>
  95
  96     <para>Boolean arguments used in configuration files can be written in
  97     various formats. For positive settings the strings
  98     <option>1</option>, <option>yes</option>, <option>true</option>
  99     and <option>on</option> are equivalent. For negative settings, the
 100     strings <option>0</option>, <option>no</option>,
 101     <option>false</option> and <option>off</option> are
 102     equivalent.</para>
 103
 104     <para>Time span values encoded in configuration files can be written in various formats. A stand-alone
 105     number specifies a time in seconds.  If suffixed with a time unit, the unit is honored. A
 106     concatenation of multiple values with units is supported, in which case the values are added
 107     up. Example: <literal>50</literal> refers to 50 seconds; <literal>2min 200ms</literal> refers to
 108     2 minutes and 200 milliseconds, i.e. 120200 ms.  The following time units are understood:
 109     <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, <literal>d</literal>,
 110     <literal>w</literal>, <literal>ms</literal>, <literal>us</literal>.  For details see
 111     <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 112
 113     <para>Various settings are allowed to be specified more than once, in which case the
 114     interpretation depends on the setting. Often, multiple settings form a list, and setting to an
 115     empty value "resets", which means that previous assignments are ignored. When this is allowed,
 116     it is mentioned in the description of the setting. Note that using multiple assignments to the
 117     same value makes the file incompatible with parsers for the XDG <filename>.desktop</filename>
 118     file format.</para>
 119   </refsect1>
 120
 121   <refsect1>
 122     <title>See Also</title>
 123     <para>
 124       <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 125     </para>
 126   </refsect1>
 127
 128 </refentry>