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="http://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>Two different directives are understood:
 102     <literal>enable</literal> may be used to enable units by default,
 103     <literal>disable</literal> to disable units by default.</para>
 104
 105     <para>If multiple lines apply to a unit name, the first matching
 106     one takes precedence over all others.</para>
 107
 108     <para>Each preset file shall be named in the style of
 109     <filename>&lt;priority&gt;-&lt;program&gt;.conf</filename>. Files
 110     in <filename>/etc/</filename> override files with the same name in
 111     <filename>/usr/lib/</filename> and <filename>/run/</filename>.
 112     Files in <filename>/run/</filename> override files with the same
 113     name in <filename>/usr/lib/</filename>. Packages should install
 114     their preset files in <filename>/usr/lib/</filename>. Files in
 115     <filename>/etc/</filename> are reserved for the local
 116     administrator, who may use this logic to override the preset files
 117     installed by vendor packages. All preset files are sorted by their
 118     filename in lexicographic order, regardless of which of the
 119     directories they reside in. If multiple files specify the same
 120     unit name, the entry in the file with the lexicographically
 121     earliest name will be applied. It is recommended to prefix all
 122     filenames with a two-digit number and a dash, to simplify the
 123     ordering of the files.</para>
 124
 125     <para>If the administrator wants to disable a preset file supplied
 126     by the vendor, the recommended way is to place a symlink to
 127     <filename>/dev/null</filename> in
 128     <filename>/etc/systemd/system-preset/</filename> bearing the same
 129     filename.</para>
 130   </refsect1>
 131
 132   <refsect1>
 133     <title>Example</title>
 134
 135     <example>
 136       <title>Default off example <filename>/usr/lib/systemd/system-preset/99-default.preset</filename>:</title>
 137
 138       <programlisting>disable *</programlisting>
 139     </example>
 140
 141     <para>This disables all units. Due to the filename prefix
 142     <literal>99-</literal>, it will be read last and hence can easily
 143     be overridden by spin or administrator preset policy or
 144     suchlike.</para>
 145
 146     <example>
 147       <title>A GNOME spin example <filename>/usr/lib/systemd/system-preset/50-gnome.preset</filename>:</title>
 148
 149       <programlisting>enable gdm.service
 150 enable colord.service
 151 enable accounts-daemon.service
 152 enable avahi-daemon.*</programlisting>
 153
 154     </example>
 155
 156     <para>This enables the three mentioned units, plus all
 157     <filename>avahi-daemon</filename> regardless of which unit type. A
 158     file like this could be useful for inclusion in a GNOME spin of a
 159     distribution. It will ensure that the units necessary for GNOME
 160     are properly enabled as they are installed. It leaves all other
 161     units untouched, and subject to other (later) preset files, for
 162     example like the one from the first example above.</para>
 163
 164     <example>
 165       <title>Administrator policy <filename>/etc/systemd/system-preset/00-lennart.preset</filename>:</title>
 166
 167       <programlisting>enable httpd.service
 168 enable sshd.service
 169 enable postfix.service
 170 disable *</programlisting>
 171     </example>
 172
 173     <para>This enables three specific services and disables all
 174     others. This is useful for administrators to specifically select
 175     the units to enable, and disable all others. Due to the filename
 176     prefix <literal>00-</literal> it will be read early and hence
 177     overrides all other preset policy files.</para>
 178   </refsect1>
 179
 180   <refsect1>
 181     <title>See Also</title>
 182     <para>
 183       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 184       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 185       <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 186     </para>
 187   </refsect1>
 188
 189 </refentry>