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       </para></listitem>
  47
  48       <listitem><para>link files, see
  49       <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  50       </para></listitem>
  51
  52       <listitem><para>netdev and network files, see
  53       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  54       <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  55       </para></listitem>
  56
  57       <listitem><para>daemon config files, see
  58       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  59       <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  60       <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  61       <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  62       <citerefentry><refentrytitle>journal-remote.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  63       <citerefentry><refentrytitle>journal-upload.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  64       <citerefentry><refentrytitle>systemd-sleep.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  65       <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  66       </para></listitem>
  67
  68       <listitem><para>nspawn files, see
  69         <citerefentry><refentrytitle>systemd.nspawn</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  70       </para></listitem>
  71     </itemizedlist>
  72     </para>
  73
  74     <para>The syntax is inspired by
  75     <ulink url="https://standards.freedesktop.org/desktop-entry-spec/latest/">XDG Desktop Entry Specification</ulink>
  76     <filename>.desktop</filename> files, which are in turn inspired by Microsoft Windows
  77     <filename>.ini</filename> files.
  78     </para>
  79
  80     <para>Each file is a plain text file divided into sections, with configuration entries in the style
  81     <replaceable>key</replaceable>=<replaceable>value</replaceable>. Whitespace immediately before or after
  82     the <literal>=</literal> is ignored. Empty lines and lines starting with <literal>#</literal> or
  83     <literal>;</literal> are ignored, which may be used for commenting.</para>
  84
  85     <para>Lines ending in a backslash are concatenated with the following line while reading and the
  86     backslash is replaced by a space character. This may be used to wrap long lines. The limit on
  87     line length is very large (currently 1 MB), but it is recommended to avoid such long lines and
  88     use multiple directives, variable substitution, or other mechanism as appropriate for the given
  89     file type. When a comment line or lines follow a line ending with a backslash, the comment block
  90     is ignored, so the continued line is concatenated with whatever follows the comment block.</para>
  91
  92     <example><programlisting>[Section A]
  93 KeyOne=value 1
  94 KeyTwo=value 2
  95
  96 # a comment
  97
  98 [Section B]
  99 Setting="something" "some thing" "…"
 100 KeyTwo=value 2 \
 101        value 2 continued
 102
 103 [Section C]
 104 KeyThree=value 3\
 105 # this line is ignored
 106 ; this line is ignored too
 107        value 3 continued
 108 </programlisting></example>
 109
 110     <para>Boolean arguments used in configuration files can be written in
 111     various formats. For positive settings the strings
 112     <option>1</option>, <option>yes</option>, <option>true</option>
 113     and <option>on</option> are equivalent. For negative settings, the
 114     strings <option>0</option>, <option>no</option>,
 115     <option>false</option> and <option>off</option> are
 116     equivalent.</para>
 117
 118     <para>Time span values encoded in configuration files can be written in various formats. A stand-alone
 119     number specifies a time in seconds.  If suffixed with a time unit, the unit is honored. A
 120     concatenation of multiple values with units is supported, in which case the values are added
 121     up. Example: <literal>50</literal> refers to 50 seconds; <literal>2min 200ms</literal> refers to
 122     2 minutes and 200 milliseconds, i.e. 120200 ms.  The following time units are understood:
 123     <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, <literal>d</literal>,
 124     <literal>w</literal>, <literal>ms</literal>, <literal>us</literal>.  For details see
 125     <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 126
 127     <para>Various settings are allowed to be specified more than once, in which case the
 128     interpretation depends on the setting. Often, multiple settings form a list, and setting to an
 129     empty value "resets", which means that previous assignments are ignored. When this is allowed,
 130     it is mentioned in the description of the setting. Note that using multiple assignments to the
 131     same value makes the file incompatible with parsers for the XDG <filename>.desktop</filename>
 132     file format.</para>
 133   </refsect1>
 134
 135   <refsect1>
 136     <title>Quoting</title>
 137
 138     <para>For settings where quoting is allowed, the following general rules apply: double quotes ("…") and
 139     single quotes ('…') may be used to wrap a whole item (the opening quote may appear only at the beginning
 140     or after whitespace that is not quoted, and the closing quote must be followed by whitespace or the end
 141     of line), in which case everything until the next matching quote becomes part of the same item. Quotes
 142     themselves are removed. C-style escapes are supported. The table below contains the list of known escape
 143     patterns. Only escape patterns which match the syntax in the table are allowed; other patterns may be
 144     added in the future and unknown patterns will result in a warning. In particular, any backslashes should
 145     be doubled. Finally, a trailing backslash (<literal>\</literal>) may be used to merge lines, as described
 146     above. UTF-8 is accepted, and hence typical unicode characters do not need to be escaped.</para>
 147
 148     <table>
 149       <title>Supported escapes</title>
 150       <tgroup cols='2'>
 151         <colspec colname='escape' />
 152         <colspec colname='meaning' />
 153         <thead>
 154           <row>
 155             <entry>Literal</entry>
 156             <entry>Actual value</entry>
 157           </row>
 158         </thead>
 159         <tbody>
 160           <row>
 161             <entry><literal>\a</literal></entry>
 162             <entry>bell</entry>
 163           </row>
 164           <row>
 165             <entry><literal>\b</literal></entry>
 166             <entry>backspace</entry>
 167           </row>
 168           <row>
 169             <entry><literal>\f</literal></entry>
 170             <entry>form feed</entry>
 171           </row>
 172           <row>
 173             <entry><literal>\n</literal></entry>
 174             <entry>newline</entry>
 175           </row>
 176           <row>
 177             <entry><literal>\r</literal></entry>
 178             <entry>carriage return</entry>
 179           </row>
 180           <row>
 181             <entry><literal>\t</literal></entry>
 182             <entry>tab</entry>
 183           </row>
 184           <row>
 185             <entry><literal>\v</literal></entry>
 186             <entry>vertical tab</entry>
 187           </row>
 188           <row>
 189             <entry><literal>\\</literal></entry>
 190             <entry>backslash</entry>
 191           </row>
 192           <row>
 193             <entry><literal>\"</literal></entry>
 194             <entry>double quotation mark</entry>
 195           </row>
 196           <row>
 197             <entry><literal>\'</literal></entry>
 198             <entry>single quotation mark</entry>
 199           </row>
 200           <row>
 201             <entry><literal>\s</literal></entry>
 202             <entry>space</entry>
 203           </row>
 204           <row>
 205             <entry><literal>\x<replaceable>xx</replaceable></literal></entry>
 206             <entry>character number <replaceable>xx</replaceable> in hexadecimal encoding</entry>
 207           </row>
 208           <row>
 209             <entry><literal>\<replaceable>nnn</replaceable></literal></entry>
 210             <entry>character number <replaceable>nnn</replaceable> in octal encoding</entry>
 211           </row>
 212           <row>
 213             <entry><literal>\u<replaceable>nnnn</replaceable></literal></entry>
 214             <entry>unicode code point <replaceable>nnnn</replaceable> in hexadecimal encoding</entry>
 215           </row>
 216           <row>
 217             <entry><literal>\U<replaceable>nnnnnnnn</replaceable></literal></entry>
 218             <entry>unicode code point <replaceable>nnnnnnnn</replaceable> in hexadecimal encoding</entry>
 219           </row>
 220         </tbody>
 221       </tgroup>
 222     </table>
 223   </refsect1>
 224
 225   <refsect1>
 226     <title>See Also</title>
 227     <para>
 228       <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 229     </para>
 230   </refsect1>
 231
 232 </refentry>