man/systemd.preset.xml

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   7 <refentry id="systemd.preset">
   8
   9   <refentryinfo>
  10     <title>systemd.preset</title>
  11     <productname>systemd</productname>
  12
  13     <authorgroup>
  14       <author>
  15         <contrib>Developer</contrib>
  16         <firstname>Lennart</firstname>
  17         <surname>Poettering</surname>
  18         <email>lennart@poettering.net</email>
  19       </author>
  20     </authorgroup>
  21   </refentryinfo>
  22
  23   <refmeta>
  24     <refentrytitle>systemd.preset</refentrytitle>
  25     <manvolnum>5</manvolnum>
  26   </refmeta>
  27
  28   <refnamediv>
  29     <refname>systemd.preset</refname>
  30     <refpurpose>Service enablement presets</refpurpose>
  31   </refnamediv>
  32
  33   <refsynopsisdiv>
  34     <para><filename>/etc/systemd/system-preset/*.preset</filename></para>
  35     <para><filename>/run/systemd/system-preset/*.preset</filename></para>
  36     <para><filename>/usr/lib/systemd/system-preset/*.preset</filename></para>
  37     <para><filename>/etc/systemd/user-preset/*.preset</filename></para>
  38     <para><filename>/run/systemd/user-preset/*.preset</filename></para>
  39     <para><filename>/usr/lib/systemd/user-preset/*.preset</filename></para>
  40   </refsynopsisdiv>
  41
  42   <refsect1>
  43     <title>Description</title>
  44
  45     <para>Preset files may be used to encode policy which units shall
  46     be enabled by default and which ones shall be disabled. They are
  47     read by <command>systemctl preset</command> (for more information
  48     see
  49     <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>)
  50     which uses this information to enable or disable a unit according
  51     to preset policy. <command>systemctl preset</command> is used by
  52     the post install scriptlets of RPM packages (or other OS package
  53     formats), to enable/disable specific units by default on package
  54     installation, enforcing distribution, spin or administrator preset
  55     policy. This allows choosing a certain set of units to be
  56     enabled/disabled even before installing the actual package.</para>
  57
  58     <para>For more information on the preset logic please have a look
  59     at the <ulink
  60     url="https://www.freedesktop.org/wiki/Software/systemd/Preset">Presets</ulink>
  61     document.</para>
  62
  63     <para>It is not recommended to ship preset files within the
  64     respective software packages implementing the units, but rather
  65     centralize them in a distribution or spin default policy, which
  66     can be amended by administrator policy.</para>
  67
  68     <para>If no preset files exist, <command>systemctl
  69     preset</command> will enable all units that are installed by
  70     default. If this is not desired and all units shall rather be
  71     disabled, it is necessary to ship a preset file with a single,
  72     catchall "<filename>disable *</filename>" line. (See example 1,
  73     below.)</para>
  74   </refsect1>
  75
  76   <refsect1>
  77     <title>Preset File Format</title>
  78
  79     <para>The preset files contain a list of directives consisting of
  80     either the word <literal>enable</literal> or
  81     <literal>disable</literal> followed by a space and a unit name
  82     (possibly with shell style wildcards), separated by newlines.
  83     Empty lines and lines whose first non-whitespace character is # or
  84     ; are ignored.</para>
  85
  86     <para>Presets must refer to the "real" unit file, and not to any aliases. See
  87     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  88     for a description of unit aliasing.</para>
  89
  90     <para>Two different directives are understood:
  91     <literal>enable</literal> may be used to enable units by default,
  92     <literal>disable</literal> to disable units by default.</para>
  93
  94     <para>If multiple lines apply to a unit name, the first matching
  95     one takes precedence over all others.</para>
  96
  97     <para>Each preset file shall be named in the style of
  98     <filename>&lt;priority&gt;-&lt;policy-name&gt;.preset</filename>. Files
  99     in <filename>/etc/</filename> override files with the same name in
 100     <filename>/usr/lib/</filename> and <filename>/run/</filename>.
 101     Files in <filename>/run/</filename> override files with the same
 102     name in <filename>/usr/lib/</filename>. Packages should install
 103     their preset files in <filename>/usr/lib/</filename>. Files in
 104     <filename>/etc/</filename> are reserved for the local
 105     administrator, who may use this logic to override the preset files
 106     installed by vendor packages. All preset files are sorted by their
 107     filename in lexicographic order, regardless of which of the
 108     directories they reside in. If multiple files specify the same
 109     unit name, the entry in the file with the lexicographically
 110     earliest name will be applied. It is recommended to prefix all
 111     filenames with a two-digit number and a dash, to simplify the
 112     ordering of the files.</para>
 113
 114     <para>If the administrator wants to disable a preset file supplied
 115     by the vendor, the recommended way is to place a symlink to
 116     <filename>/dev/null</filename> in
 117     <filename>/etc/systemd/system-preset/</filename> bearing the same
 118     filename.</para>
 119   </refsect1>
 120
 121   <refsect1>
 122     <title>Examples</title>
 123
 124     <example>
 125       <title>Default to off</title>
 126
 127       <programlisting># /usr/lib/systemd/system-preset/99-default.preset
 128
 129 disable *</programlisting>
 130     </example>
 131
 132     <para>This disables all units. Due to the filename prefix
 133     <literal>99-</literal>, it will be read last and hence can easily
 134     be overridden by spin or administrator preset policy.</para>
 135
 136     <example>
 137       <title>A GNOME spin</title>
 138
 139       <programlisting># /usr/lib/systemd/system-preset/50-gnome.preset
 140
 141 enable gdm.service
 142 enable colord.service
 143 enable accounts-daemon.service
 144 enable avahi-daemon.*</programlisting>
 145
 146     </example>
 147
 148     <para>This enables the three mentioned units, plus all
 149     <filename>avahi-daemon</filename> regardless of which unit type. A
 150     file like this could be useful for inclusion in a GNOME spin of a
 151     distribution. It will ensure that the units necessary for GNOME
 152     are properly enabled as they are installed. It leaves all other
 153     units untouched, and subject to other (later) preset files, for
 154     example like the one from the first example above.</para>
 155
 156     <example>
 157       <title>Administrator policy</title>
 158
 159       <programlisting># /etc/systemd/system-preset/00-lennart.preset
 160
 161 enable httpd.service
 162 enable sshd.service
 163 enable postfix.service
 164 disable *</programlisting>
 165     </example>
 166
 167     <para>This enables three specific services and disables all
 168     others. This is useful for administrators to specifically select
 169     the units to enable, and disable all others. Due to the filename
 170     prefix <literal>00-</literal> it will be read early and
 171     override all other preset policy files.</para>
 172   </refsect1>
 173
 174   <refsect1>
 175     <title>See Also</title>
 176     <para>
 177       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 178       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 179       <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 180     </para>
 181   </refsect1>
 182
 183 </refentry>