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 <literal>#</literal> or
  74     <literal>;</literal> are ignored. Multiple instance names for unit
  75     templates may be specified as a space separated list at the end of
  76     the line instead of the customary position between <literal>@</literal>
  77     and the unit suffix.</para>
  78
  79     <para>Presets must refer to the "real" unit file, and not to any aliases. See
  80     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  81     for a description of unit aliasing.</para>
  82
  83     <para>Two different directives are understood:
  84     <literal>enable</literal> may be used to enable units by default,
  85     <literal>disable</literal> to disable units by default.</para>
  86
  87     <para>If multiple lines apply to a unit name, the first matching
  88     one takes precedence over all others.</para>
  89
  90     <para>Each preset file shall be named in the style of
  91     <filename>&lt;priority&gt;-&lt;policy-name&gt;.preset</filename>. Files
  92     in <filename>/etc/</filename> override files with the same name in
  93     <filename>/usr/lib/</filename> and <filename>/run/</filename>.
  94     Files in <filename>/run/</filename> override files with the same
  95     name in <filename>/usr/lib/</filename>. Packages should install
  96     their preset files in <filename>/usr/lib/</filename>. Files in
  97     <filename>/etc/</filename> are reserved for the local
  98     administrator, who may use this logic to override the preset files
  99     installed by vendor packages. All preset files are sorted by their
 100     filename in lexicographic order, regardless of which of the
 101     directories they reside in. If multiple files specify the same
 102     unit name, the entry in the file with the lexicographically
 103     earliest name will be applied. It is recommended to prefix all
 104     filenames with a two-digit number and a dash, to simplify the
 105     ordering of the files.</para>
 106
 107     <para>If the administrator wants to disable a preset file supplied
 108     by the vendor, the recommended way is to place a symlink to
 109     <filename>/dev/null</filename> in
 110     <filename>/etc/systemd/system-preset/</filename> bearing the same
 111     filename.</para>
 112   </refsect1>
 113
 114   <refsect1>
 115     <title>Examples</title>
 116
 117     <example>
 118       <title>Default to off</title>
 119
 120       <programlisting># /usr/lib/systemd/system-preset/99-default.preset
 121
 122 disable *</programlisting>
 123     </example>
 124
 125     <para>This disables all units. Due to the filename prefix
 126     <literal>99-</literal>, it will be read last and hence can easily
 127     be overridden by spin or administrator preset policy.</para>
 128
 129     <example>
 130       <title>Enable multiple template instances</title>
 131
 132       <programlisting># /usr/lib/systemd/system-preset/80-dirsrv.preset
 133
 134 enable dirsrv@.service foo bar baz</programlisting>
 135     </example>
 136
 137     <para>This enables all three of <filename>dirsrv@foo.service</filename>,
 138     <filename>dirsrv@bar.service</filename> and <filename>dirsrv@baz.service</filename>.</para>
 139
 140     <example>
 141       <title>A GNOME spin</title>
 142
 143       <programlisting># /usr/lib/systemd/system-preset/50-gnome.preset
 144
 145 enable gdm.service
 146 enable colord.service
 147 enable accounts-daemon.service
 148 enable avahi-daemon.*</programlisting>
 149
 150     </example>
 151
 152     <para>This enables the three mentioned units, plus all
 153     <filename>avahi-daemon</filename> regardless of which unit type. A
 154     file like this could be useful for inclusion in a GNOME spin of a
 155     distribution. It will ensure that the units necessary for GNOME
 156     are properly enabled as they are installed. It leaves all other
 157     units untouched, and subject to other (later) preset files, for
 158     example like the one from the first example above.</para>
 159
 160     <example>
 161       <title>Administrator policy</title>
 162
 163       <programlisting># /etc/systemd/system-preset/00-lennart.preset
 164
 165 enable httpd.service
 166 enable sshd.service
 167 enable postfix.service
 168 disable *</programlisting>
 169     </example>
 170
 171     <para>This enables three specific services and disables all
 172     others. This is useful for administrators to specifically select
 173     the units to enable, and disable all others. Due to the filename
 174     prefix <literal>00-</literal> it will be read early and
 175     override all other preset policy files.</para>
 176   </refsect1>
 177
 178   <refsect1>
 179     <title>See Also</title>
 180     <para>
 181       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 182       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 183       <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 184     </para>
 185   </refsect1>
 186
 187 </refentry>