man/systemd.preset.xml

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  22 <refentry id="systemd.preset">
  23
  24   <refentryinfo>
  25     <title>systemd.preset</title>
  26     <productname>systemd</productname>
  27
  28     <authorgroup>
  29       <author>
  30         <contrib>Developer</contrib>
  31         <firstname>Lennart</firstname>
  32         <surname>Poettering</surname>
  33         <email>lennart@poettering.net</email>
  34       </author>
  35     </authorgroup>
  36   </refentryinfo>
  37
  38   <refmeta>
  39     <refentrytitle>systemd.preset</refentrytitle>
  40     <manvolnum>5</manvolnum>
  41   </refmeta>
  42
  43   <refnamediv>
  44     <refname>systemd.preset</refname>
  45     <refpurpose>Service enablement presets</refpurpose>
  46   </refnamediv>
  47
  48   <refsynopsisdiv>
  49     <para><filename>/etc/systemd/system-preset/*.preset</filename></para>
  50     <para><filename>/run/systemd/system-preset/*.preset</filename></para>
  51     <para><filename>/usr/lib/systemd/system-preset/*.preset</filename></para>
  52     <para><filename>/etc/systemd/user-preset/*.preset</filename></para>
  53     <para><filename>/run/systemd/user-preset/*.preset</filename></para>
  54     <para><filename>/usr/lib/systemd/user-preset/*.preset</filename></para>
  55   </refsynopsisdiv>
  56
  57   <refsect1>
  58     <title>Description</title>
  59
  60     <para>Preset files may be used to encode policy which units shall
  61     be enabled by default and which ones shall be disabled. They are
  62     read by <command>systemctl preset</command> (for more information
  63     see
  64     <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>)
  65     which uses this information to enable or disable a unit according
  66     to preset policy. <command>systemctl preset</command> is used by
  67     the post install scriptlets of RPM packages (or other OS package
  68     formats), to enable/disable specific units by default on package
  69     installation, enforcing distribution, spin or administrator preset
  70     policy. This allows choosing a certain set of units to be
  71     enabled/disabled even before installing the actual package.</para>
  72
  73     <para>For more information on the preset logic please have a look
  74     at the <ulink
  75     url="https://www.freedesktop.org/wiki/Software/systemd/Preset">Presets</ulink>
  76     document.</para>
  77
  78     <para>It is not recommended to ship preset files within the
  79     respective software packages implementing the units, but rather
  80     centralize them in a distribution or spin default policy, which
  81     can be amended by administrator policy.</para>
  82
  83     <para>If no preset files exist, <command>systemctl
  84     preset</command> will enable all units that are installed by
  85     default. If this is not desired and all units shall rather be
  86     disabled, it is necessary to ship a preset file with a single,
  87     catchall "<filename>disable *</filename>" line. (See example 1,
  88     below.)</para>
  89   </refsect1>
  90
  91   <refsect1>
  92     <title>Preset File Format</title>
  93
  94     <para>The preset files contain a list of directives consisting of
  95     either the word <literal>enable</literal> or
  96     <literal>disable</literal> followed by a space and a unit name
  97     (possibly with shell style wildcards), separated by newlines.
  98     Empty lines and lines whose first non-whitespace character is # or
  99     ; are ignored.</para>
 100
 101     <para>Presets must refer to the "real" unit file, and not to any aliases. See
 102     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 103     for a description of unit aliasing.</para>
 104
 105     <para>Two different directives are understood:
 106     <literal>enable</literal> may be used to enable units by default,
 107     <literal>disable</literal> to disable units by default.</para>
 108
 109     <para>If multiple lines apply to a unit name, the first matching
 110     one takes precedence over all others.</para>
 111
 112     <para>Each preset file shall be named in the style of
 113     <filename>&lt;priority&gt;-&lt;policy-name&gt;.preset</filename>. Files
 114     in <filename>/etc/</filename> override files with the same name in
 115     <filename>/usr/lib/</filename> and <filename>/run/</filename>.
 116     Files in <filename>/run/</filename> override files with the same
 117     name in <filename>/usr/lib/</filename>. Packages should install
 118     their preset files in <filename>/usr/lib/</filename>. Files in
 119     <filename>/etc/</filename> are reserved for the local
 120     administrator, who may use this logic to override the preset files
 121     installed by vendor packages. All preset files are sorted by their
 122     filename in lexicographic order, regardless of which of the
 123     directories they reside in. If multiple files specify the same
 124     unit name, the entry in the file with the lexicographically
 125     earliest name will be applied. It is recommended to prefix all
 126     filenames with a two-digit number and a dash, to simplify the
 127     ordering of the files.</para>
 128
 129     <para>If the administrator wants to disable a preset file supplied
 130     by the vendor, the recommended way is to place a symlink to
 131     <filename>/dev/null</filename> in
 132     <filename>/etc/systemd/system-preset/</filename> bearing the same
 133     filename.</para>
 134   </refsect1>
 135
 136   <refsect1>
 137     <title>Example</title>
 138
 139     <example>
 140       <title>Default off example <filename>/usr/lib/systemd/system-preset/99-default.preset</filename>:</title>
 141
 142       <programlisting>disable *</programlisting>
 143     </example>
 144
 145     <para>This disables all units. Due to the filename prefix
 146     <literal>99-</literal>, it will be read last and hence can easily
 147     be overridden by spin or administrator preset policy or
 148     suchlike.</para>
 149
 150     <example>
 151       <title>A GNOME spin example <filename>/usr/lib/systemd/system-preset/50-gnome.preset</filename>:</title>
 152
 153       <programlisting>enable gdm.service
 154 enable colord.service
 155 enable accounts-daemon.service
 156 enable avahi-daemon.*</programlisting>
 157
 158     </example>
 159
 160     <para>This enables the three mentioned units, plus all
 161     <filename>avahi-daemon</filename> regardless of which unit type. A
 162     file like this could be useful for inclusion in a GNOME spin of a
 163     distribution. It will ensure that the units necessary for GNOME
 164     are properly enabled as they are installed. It leaves all other
 165     units untouched, and subject to other (later) preset files, for
 166     example like the one from the first example above.</para>
 167
 168     <example>
 169       <title>Administrator policy <filename>/etc/systemd/system-preset/00-lennart.preset</filename>:</title>
 170
 171       <programlisting>enable httpd.service
 172 enable sshd.service
 173 enable postfix.service
 174 disable *</programlisting>
 175     </example>
 176
 177     <para>This enables three specific services and disables all
 178     others. This is useful for administrators to specifically select
 179     the units to enable, and disable all others. Due to the filename
 180     prefix <literal>00-</literal> it will be read early and hence
 181     overrides all other preset policy files.</para>
 182   </refsect1>
 183
 184   <refsect1>
 185     <title>See Also</title>
 186     <para>
 187       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 188       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 189       <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 190     </para>
 191   </refsect1>
 192
 193 </refentry>