man/systemd.syntax.xml

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  10 <refentry id="systemd.syntax">
  11
  12   <refentryinfo>
  13     <title>systemd.syntax</title>
  14     <productname>systemd</productname>
  15   </refentryinfo>
  16
  17   <refmeta>
  18     <refentrytitle>systemd.syntax</refentrytitle>
  19     <manvolnum>7</manvolnum>
  20   </refmeta>
  21
  22   <refnamediv>
  23     <refname>systemd.syntax</refname>
  24     <refpurpose>General syntax of systemd configuration files</refpurpose>
  25   </refnamediv>
  26
  27   <refsect1>
  28     <title>Introduction</title>
  29
  30     <para>This page describes the basic principles of configuration files used by
  31     <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  32     and related programs for:
  33     <itemizedlist>
  34       <listitem><para>systemd unit files, see
  35       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  36       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  37       <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  38       <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  39       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  40       <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  41       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  42       <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  43       <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  44       <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  45       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  46       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry></para></listitem>
  47
  48       <listitem><para>daemon config files, see
  49       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  50       <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  51       <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  52       <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  53       <citerefentry><refentrytitle>journal-remote.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  54       <citerefentry><refentrytitle>journal-upload.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  55       <citerefentry><refentrytitle>systemd-sleep.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  56       <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  57       </para></listitem>
  58     </itemizedlist>
  59     </para>
  60
  61     <para>The syntax is inspired by
  62     <ulink url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG Desktop Entry Specification</ulink>
  63     <filename>.desktop</filename> files, which are in turn inspired by Microsoft Windows
  64     <filename>.ini</filename> files.
  65     </para>
  66
  67     <para>Each file is a plain text file divided into sections, with configuration entries in the
  68     style <replaceable>key</replaceable>=<replaceable>value</replaceable>.
  69     Empty lines and lines starting with <literal>#</literal> or <literal>;</literal> are
  70     ignored, which may be used for commenting.</para>
  71
  72     <para>Lines ending in a backslash are concatenated with the following line while reading and the
  73     backslash is replaced by a space character. This may be used to wrap long lines. The limit on
  74     line length is very large (currently 1 MB), but it is recommended to avoid such long lines and
  75     use multiple directives, variable substitution, or other mechanism as appropriate for the given
  76     file type.</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 </programlisting></example>
  89
  90     <para>Boolean arguments used in configuration files can be written in
  91     various formats. For positive settings the strings
  92     <option>1</option>, <option>yes</option>, <option>true</option>
  93     and <option>on</option> are equivalent. For negative settings, the
  94     strings <option>0</option>, <option>no</option>,
  95     <option>false</option> and <option>off</option> are
  96     equivalent.</para>
  97
  98     <para>Time span values encoded in configuration files can be written in various formats. A stand-alone
  99     number specifies a time in seconds.  If suffixed with a time unit, the unit is honored. A
 100     concatenation of multiple values with units is supported, in which case the values are added
 101     up. Example: <literal>50</literal> refers to 50 seconds; <literal>2min 200ms</literal> refers to
 102     2 minutes and 200 milliseconds, i.e. 120200 ms.  The following time units are understood:
 103     <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, <literal>d</literal>,
 104     <literal>w</literal>, <literal>ms</literal>, <literal>us</literal>.  For details see
 105     <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 106
 107     <para>Various settings are allowed to be specified more than once, in which case the
 108     interpretation depends on the setting. Often, multiple settings form a list, and setting to an
 109     empty value "resets", which means that previous assignments are ignored. When this is allowed,
 110     it is mentioned in the description of the setting. Note that using multiple assignments to the
 111     same value makes the file incompatible with parsers for the XDG <filename>.desktop</filename>
 112     file format.</para>
 113   </refsect1>
 114
 115   <refsect1>
 116     <title>See Also</title>
 117     <para>
 118       <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 119     </para>
 120   </refsect1>
 121
 122 </refentry>