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>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
  78     style <replaceable>key</replaceable>=<replaceable>value</replaceable>.
  79     Whitespace immediately before or after the <literal>=</literal> is ignored. Empty lines and lines starting with <literal>#</literal> or <literal>;</literal> are
  80     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]
  90 KeyOne=value 1
  91 KeyTwo=value 2
  92
  93 # a comment
  94
  95 [Section B]
  96 Setting="something" "some thing" "…"
  97 KeyTwo=value 2 \
  98        value 2 continued
  99
 100 [Section C]
 101 KeyThree=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>See Also</title>
 134     <para>
 135       <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 136     </para>
 137   </refsect1>
 138
 139 </refentry>