man/systemd.preset.xml

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   6 <refentry id="systemd.preset">
   7
   8   <refentryinfo>
   9     <title>systemd.preset</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>systemd.preset</refentrytitle>
  15     <manvolnum>5</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>systemd.preset</refname>
  20     <refpurpose>Service enablement presets</refpurpose>
  21   </refnamediv>
  22
  23   <refsynopsisdiv>
  24     <para><filename>/etc/systemd/system-preset/*.preset</filename></para>
  25     <para><filename>/run/systemd/system-preset/*.preset</filename></para>
  26     <para><filename>/usr/lib/systemd/system-preset/*.preset</filename></para>
  27     <para><filename>/etc/systemd/user-preset/*.preset</filename></para>
  28     <para><filename>/run/systemd/user-preset/*.preset</filename></para>
  29     <para><filename>/usr/lib/systemd/user-preset/*.preset</filename></para>
  30   </refsynopsisdiv>
  31
  32   <refsect1>
  33     <title>Description</title>
  34
  35     <para>Preset files may be used to encode policy which units shall
  36     be enabled by default and which ones shall be disabled. They are
  37     read by <command>systemctl preset</command> (for more information
  38     see
  39     <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>)
  40     which uses this information to enable or disable a unit according
  41     to preset policy. <command>systemctl preset</command> is used by
  42     the post install scriptlets of RPM packages (or other OS package
  43     formats), to enable/disable specific units by default on package
  44     installation, enforcing distribution, spin or administrator preset
  45     policy. This allows choosing a certain set of units to be
  46     enabled/disabled even before installing the actual package.</para>
  47
  48     <para>For more information on the preset logic please have a look
  49     at the <ulink
  50     url="https://www.freedesktop.org/wiki/Software/systemd/Preset">Presets</ulink>
  51     document.</para>
  52
  53     <para>It is not recommended to ship preset files within the
  54     respective software packages implementing the units, but rather
  55     centralize them in a distribution or spin default policy, which
  56     can be amended by administrator policy.</para>
  57
  58     <para>If no preset files exist, <command>systemctl
  59     preset</command> will enable all units that are installed by
  60     default. If this is not desired and all units shall rather be
  61     disabled, it is necessary to ship a preset file with a single,
  62     catchall "<filename>disable *</filename>" line. (See example 1,
  63     below.)</para>
  64   </refsect1>
  65
  66   <refsect1>
  67     <title>Preset File Format</title>
  68
  69     <para>The preset files contain a list of directives consisting of
  70     either the word <literal>enable</literal> or
  71     <literal>disable</literal> followed by a space and a unit name
  72     (possibly with shell style wildcards), separated by newlines.
  73     Empty lines and lines whose first non-whitespace character is # or
  74     ; are ignored.</para>
  75
  76     <para>Presets must refer to the "real" unit file, and not to any aliases. See
  77     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  78     for a description of unit aliasing.</para>
  79
  80     <para>Two different directives are understood:
  81     <literal>enable</literal> may be used to enable units by default,
  82     <literal>disable</literal> to disable units by default.</para>
  83
  84     <para>If multiple lines apply to a unit name, the first matching
  85     one takes precedence over all others.</para>
  86
  87     <para>Each preset file shall be named in the style of
  88     <filename>&lt;priority&gt;-&lt;policy-name&gt;.preset</filename>. Files
  89     in <filename>/etc/</filename> override files with the same name in
  90     <filename>/usr/lib/</filename> and <filename>/run/</filename>.
  91     Files in <filename>/run/</filename> override files with the same
  92     name in <filename>/usr/lib/</filename>. Packages should install
  93     their preset files in <filename>/usr/lib/</filename>. Files in
  94     <filename>/etc/</filename> are reserved for the local
  95     administrator, who may use this logic to override the preset files
  96     installed by vendor packages. All preset files are sorted by their
  97     filename in lexicographic order, regardless of which of the
  98     directories they reside in. If multiple files specify the same
  99     unit name, the entry in the file with the lexicographically
 100     earliest name will be applied. It is recommended to prefix all
 101     filenames with a two-digit number and a dash, to simplify the
 102     ordering of the files.</para>
 103
 104     <para>If the administrator wants to disable a preset file supplied
 105     by the vendor, the recommended way is to place a symlink to
 106     <filename>/dev/null</filename> in
 107     <filename>/etc/systemd/system-preset/</filename> bearing the same
 108     filename.</para>
 109   </refsect1>
 110
 111   <refsect1>
 112     <title>Examples</title>
 113
 114     <example>
 115       <title>Default to off</title>
 116
 117       <programlisting># /usr/lib/systemd/system-preset/99-default.preset
 118
 119 disable *</programlisting>
 120     </example>
 121
 122     <para>This disables all units. Due to the filename prefix
 123     <literal>99-</literal>, it will be read last and hence can easily
 124     be overridden by spin or administrator preset policy.</para>
 125
 126     <example>
 127       <title>A GNOME spin</title>
 128
 129       <programlisting># /usr/lib/systemd/system-preset/50-gnome.preset
 130
 131 enable gdm.service
 132 enable colord.service
 133 enable accounts-daemon.service
 134 enable avahi-daemon.*</programlisting>
 135
 136     </example>
 137
 138     <para>This enables the three mentioned units, plus all
 139     <filename>avahi-daemon</filename> regardless of which unit type. A
 140     file like this could be useful for inclusion in a GNOME spin of a
 141     distribution. It will ensure that the units necessary for GNOME
 142     are properly enabled as they are installed. It leaves all other
 143     units untouched, and subject to other (later) preset files, for
 144     example like the one from the first example above.</para>
 145
 146     <example>
 147       <title>Administrator policy</title>
 148
 149       <programlisting># /etc/systemd/system-preset/00-lennart.preset
 150
 151 enable httpd.service
 152 enable sshd.service
 153 enable postfix.service
 154 disable *</programlisting>
 155     </example>
 156
 157     <para>This enables three specific services and disables all
 158     others. This is useful for administrators to specifically select
 159     the units to enable, and disable all others. Due to the filename
 160     prefix <literal>00-</literal> it will be read early and
 161     override all other preset policy files.</para>
 162   </refsect1>
 163
 164   <refsect1>
 165     <title>See Also</title>
 166     <para>
 167       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 168       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 169       <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 170     </para>
 171   </refsect1>
 172
 173 </refentry>