man/systemd-udevd.service.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="systemd-udevd.service"
   7           xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>systemd-udevd.service</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>systemd-udevd.service</refentrytitle>
  16     <manvolnum>8</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>systemd-udevd.service</refname>
  21     <refname>systemd-udevd-control.socket</refname>
  22     <refname>systemd-udevd-kernel.socket</refname>
  23     <refname>systemd-udevd</refname>
  24     <refpurpose>Device event managing daemon</refpurpose>
  25   </refnamediv>
  26
  27   <refsynopsisdiv>
  28     <para><filename>systemd-udevd.service</filename></para>
  29     <para><filename>systemd-udevd-control.socket</filename></para>
  30     <para><filename>systemd-udevd-kernel.socket</filename></para>
  31
  32     <cmdsynopsis>
  33       <command>/usr/lib/systemd/systemd-udevd</command>
  34       <arg><option>--daemon</option></arg>
  35       <arg><option>--debug</option></arg>
  36       <arg><option>--children-max=</option></arg>
  37       <arg><option>--exec-delay=</option></arg>
  38       <arg><option>--event-timeout=</option></arg>
  39       <arg><option>--resolve-names=early|late|never</option></arg>
  40       <arg><option>--version</option></arg>
  41       <arg><option>--help</option></arg>
  42     </cmdsynopsis>
  43
  44   </refsynopsisdiv>
  45
  46   <refsect1><title>Description</title>
  47     <para><command>systemd-udevd</command> listens to kernel uevents.
  48     For every event, systemd-udevd executes matching instructions
  49     specified in udev rules. See <citerefentry>
  50     <refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum>
  51     </citerefentry>.</para>
  52
  53     <para>The behavior of the daemon can be configured using
  54     <citerefentry><refentrytitle>udev.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  55     its command line options, environment variables, and on the kernel
  56     command line, or changed dynamically with <command>udevadm
  57     control</command>.
  58     </para>
  59   </refsect1>
  60
  61   <refsect1><title>Options</title>
  62     <variablelist>
  63       <varlistentry>
  64         <term><option>-d</option></term>
  65         <term><option>--daemon</option></term>
  66         <listitem>
  67           <para>Detach and run in the background.</para>
  68         </listitem>
  69       </varlistentry>
  70
  71       <varlistentry>
  72         <term><option>-D</option></term>
  73         <term><option>--debug</option></term>
  74         <listitem>
  75           <para>Print debug messages to standard error.</para>
  76         </listitem>
  77       </varlistentry>
  78
  79       <varlistentry>
  80         <term><option>-c=</option></term>
  81         <term><option>--children-max=</option></term>
  82         <listitem>
  83           <para>Limit the number of events executed in parallel.</para>
  84         </listitem>
  85       </varlistentry>
  86
  87       <varlistentry>
  88         <term><option>-e=</option></term>
  89         <term><option>--exec-delay=</option></term>
  90         <listitem>
  91           <para>Delay the execution of <varname>RUN</varname>
  92           instructions by the given number of seconds. This option
  93           might be useful when debugging system crashes during
  94           coldplug caused by loading non-working kernel
  95           modules.</para>
  96         </listitem>
  97       </varlistentry>
  98
  99       <varlistentry>
 100         <term><option>-t=</option></term>
 101         <term><option>--event-timeout=</option></term>
 102         <listitem>
 103           <para>Set the number of seconds to wait for events to finish. After
 104           this time, the event will be terminated. The default is 180 seconds.</para>
 105         </listitem>
 106       </varlistentry>
 107
 108       <varlistentry>
 109         <term><option>-N=</option></term>
 110         <term><option>--resolve-names=</option></term>
 111         <listitem>
 112           <para>Specify when systemd-udevd should resolve names of users and groups.
 113           When set to <option>early</option> (the default), names will be
 114           resolved when the rules are parsed.  When set to
 115           <option>late</option>, names will be resolved for every event.
 116           When set to <option>never</option>, names will never be resolved
 117           and all devices will be owned by root.</para>
 118         </listitem>
 119       </varlistentry>
 120
 121       <xi:include href="standard-options.xml" xpointer="help" />
 122       <xi:include href="standard-options.xml" xpointer="version" />
 123     </variablelist>
 124   </refsect1>
 125
 126   <refsect1><title>Kernel command line</title>
 127     <variablelist class='kernel-commandline-options'>
 128       <para>Parameters starting with "rd." will be read when
 129       <command>systemd-udevd</command> is used in an initrd.</para>
 130       <varlistentry>
 131         <term><varname>udev.log_priority=</varname></term>
 132         <term><varname>rd.udev.log_priority=</varname></term>
 133         <listitem>
 134           <para>Set the log level.</para>
 135         </listitem>
 136       </varlistentry>
 137       <varlistentry>
 138         <term><varname>udev.children_max=</varname></term>
 139         <term><varname>rd.udev.children_max=</varname></term>
 140         <listitem>
 141           <para>Limit the number of events executed in parallel.</para>
 142         </listitem>
 143       </varlistentry>
 144       <varlistentry>
 145         <term><varname>udev.exec_delay=</varname></term>
 146         <term><varname>rd.udev.exec_delay=</varname></term>
 147         <listitem>
 148           <para>Delay the execution of <varname>RUN</varname> instructions by the given
 149           number of seconds. This option might be useful when
 150           debugging system crashes during coldplug caused by loading
 151           non-working kernel modules.</para>
 152         </listitem>
 153       </varlistentry>
 154       <varlistentry>
 155         <term><varname>udev.event_timeout=</varname></term>
 156         <term><varname>rd.udev.event_timeout=</varname></term>
 157         <listitem>
 158           <para>Wait for events to finish up to the given number
 159           of seconds. This option might be useful if events are
 160           terminated due to kernel drivers taking too long to initialize.</para>
 161         </listitem>
 162       </varlistentry>
 163       <varlistentry>
 164         <term><varname>net.ifnames=</varname></term>
 165         <listitem>
 166           <para>Network interfaces are renamed to give them predictable names
 167           when possible. It is enabled by default; specifying 0 disables it.</para>
 168         </listitem>
 169       </varlistentry>
 170       <varlistentry>
 171         <term><varname>net.naming-scheme=</varname></term>
 172         <listitem>
 173           <para>Network interfaces are renamed to give them predictable names when possible (unless
 174           <varname>net.ifnames=0</varname> is specified, see above). The names are derived from various
 175           device metadata fields. Newer versions of <filename>systemd-udevd.service</filename> take more of
 176           these fields into account, improving (and thus possibly changing) the names used for the same
 177           devices. With this kernel command line option it is possible to pick a specific version of this
 178           algorithm. It expects a naming scheme identifier as argument. Currently the following identifiers
 179           are known: <literal>v238</literal>, <literal>v239</literal>, <literal>v240</literal> which each
 180           implement the naming scheme that was the default in the indicated systemd version. In addition,
 181           <literal>latest</literal> may be used to designate the latest scheme known (to this particular
 182           version of <filename>systemd-udevd.service</filename>).</para>
 183
 184           <para>Note that selecting a specific scheme is not sufficient to fully stabilize interface naming:
 185           the naming is generally derived from driver attributes exposed by the kernel. As the kernel is
 186           updated, previously missing attributes <filename>systemd-udevd.service</filename> is checking might
 187           appear, which affects older name derivation algorithms, too.</para>
 188         </listitem>
 189       </varlistentry>
 190     </variablelist>
 191     <!-- when adding entries here, consider also adding them
 192          in kernel-command-line.xml -->
 193  </refsect1>
 194
 195   <refsect1>
 196     <title>See Also</title>
 197     <para>
 198       <citerefentry><refentrytitle>udev.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 199       <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 200       <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 201     </para>
 202   </refsect1>
 203 </refentry>