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>,
  46       <citerefentry><refentrytitle>systemd.nspawn</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  47       </para></listitem>
  48
  49       <listitem><para>daemon config files, see
  50       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  51       <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  52       <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  53       <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  54       <citerefentry><refentrytitle>journal-remote.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  55       <citerefentry><refentrytitle>journal-upload.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  56       <citerefentry><refentrytitle>systemd-sleep.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  57       <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  58       </para></listitem>
  59     </itemizedlist>
  60     </para>
  61
  62     <para>The syntax is inspired by
  63     <ulink url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG Desktop Entry Specification</ulink>
  64     <filename>.desktop</filename> files, which are in turn inspired by Microsoft Windows
  65     <filename>.ini</filename> files.
  66     </para>
  67
  68     <para>Each file is a plain text file divided into sections, with configuration entries in the
  69     style <replaceable>key</replaceable>=<replaceable>value</replaceable>.
  70     Whitespace immediately before or after the <literal>=</literal> is ignored. Empty lines and lines starting with <literal>#</literal> or <literal>;</literal> are
  71     ignored, which may be used for commenting.</para>
  72
  73     <para>Lines ending in a backslash are concatenated with the following line while reading and the
  74     backslash is replaced by a space character. This may be used to wrap long lines. The limit on
  75     line length is very large (currently 1 MB), but it is recommended to avoid such long lines and
  76     use multiple directives, variable substitution, or other mechanism as appropriate for the given
  77     file type. When a comment line or lines follow a line ending with a backslash, the comment block
  78     is ignored, so the continued line is concatenated with whatever follows the comment block.</para>
  79
  80     <example><programlisting>[Section A]
  81 KeyOne=value 1
  82 KeyTwo=value 2
  83
  84 # a comment
  85
  86 [Section B]
  87 Setting="something" "some thing" "…"
  88 KeyTwo=value 2 \
  89        value 2 continued
  90
  91 [Section C]
  92 KeyThree=value 2\
  93 # this line is ignored
  94 ; this line is ignored too
  95        value 2 continued
  96 </programlisting></example>
  97
  98     <para>Boolean arguments used in configuration files can be written in
  99     various formats. For positive settings the strings
 100     <option>1</option>, <option>yes</option>, <option>true</option>
 101     and <option>on</option> are equivalent. For negative settings, the
 102     strings <option>0</option>, <option>no</option>,
 103     <option>false</option> and <option>off</option> are
 104     equivalent.</para>
 105
 106     <para>Time span values encoded in configuration files can be written in various formats. A stand-alone
 107     number specifies a time in seconds.  If suffixed with a time unit, the unit is honored. A
 108     concatenation of multiple values with units is supported, in which case the values are added
 109     up. Example: <literal>50</literal> refers to 50 seconds; <literal>2min 200ms</literal> refers to
 110     2 minutes and 200 milliseconds, i.e. 120200 ms.  The following time units are understood:
 111     <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, <literal>d</literal>,
 112     <literal>w</literal>, <literal>ms</literal>, <literal>us</literal>.  For details see
 113     <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 114
 115     <para>Various settings are allowed to be specified more than once, in which case the
 116     interpretation depends on the setting. Often, multiple settings form a list, and setting to an
 117     empty value "resets", which means that previous assignments are ignored. When this is allowed,
 118     it is mentioned in the description of the setting. Note that using multiple assignments to the
 119     same value makes the file incompatible with parsers for the XDG <filename>.desktop</filename>
 120     file format.</para>
 121   </refsect1>
 122
 123   <refsect1>
 124     <title>See Also</title>
 125     <para>
 126       <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 127     </para>
 128   </refsect1>
 129
 130 </refentry>