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