systemd/man/systemd-udevd.service.xml

<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<!--
  SPDX-License-Identifier: LGPL-2.1+
-->

<refentry id="systemd-udevd.service"
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-udevd.service</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-udevd.service</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-udevd.service</refname>
    <refname>systemd-udevd-control.socket</refname>
    <refname>systemd-udevd-kernel.socket</refname>
    <refname>systemd-udevd</refname>
    <refpurpose>Device event managing daemon</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>systemd-udevd.service</filename></para>
    <para><filename>systemd-udevd-control.socket</filename></para>
    <para><filename>systemd-udevd-kernel.socket</filename></para>

    <cmdsynopsis>
      <command>/usr/lib/systemd/systemd-udevd</command>
      <arg><option>--daemon</option></arg>
      <arg><option>--debug</option></arg>
      <arg><option>--children-max=</option></arg>
      <arg><option>--exec-delay=</option></arg>
      <arg><option>--event-timeout=</option></arg>
      <arg><option>--resolve-names=early|late|never</option></arg>
      <arg><option>--version</option></arg>
      <arg><option>--help</option></arg>
    </cmdsynopsis>

  </refsynopsisdiv>

  <refsect1><title>Description</title>
    <para><command>systemd-udevd</command> listens to kernel uevents.
    For every event, systemd-udevd executes matching instructions
    specified in udev rules. See <citerefentry>
    <refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum>
    </citerefentry>.</para>

    <para>The behavior of the daemon can be configured using
    <citerefentry><refentrytitle>udev.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    its command line options, environment variables, and on the kernel
    command line, or changed dynamically with <command>udevadm
    control</command>.
    </para>
  </refsect1>

  <refsect1><title>Options</title>
    <variablelist>
      <varlistentry>
        <term><option>-d</option></term>
        <term><option>--daemon</option></term>
        <listitem>
          <para>Detach and run in the background.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-D</option></term>
        <term><option>--debug</option></term>
        <listitem>
          <para>Print debug messages to standard error.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-c=</option></term>
        <term><option>--children-max=</option></term>
        <listitem>
          <para>Limit the number of events executed in parallel.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-e=</option></term>
        <term><option>--exec-delay=</option></term>
        <listitem>
          <para>Delay the execution of <varname>RUN</varname>
          instructions by the given number of seconds. This option
          might be useful when debugging system crashes during
          coldplug caused by loading non-working kernel
          modules.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-t=</option></term>
        <term><option>--event-timeout=</option></term>
        <listitem>
          <para>Set the number of seconds to wait for events to finish. After
          this time, the event will be terminated. The default is 180 seconds.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-N=</option></term>
        <term><option>--resolve-names=</option></term>
        <listitem>
          <para>Specify when systemd-udevd should resolve names of users and groups.
          When set to <option>early</option> (the default), names will be
          resolved when the rules are parsed.  When set to
          <option>late</option>, names will be resolved for every event.
          When set to <option>never</option>, names will never be resolved
          and all devices will be owned by root.</para>
        </listitem>
      </varlistentry>

      <xi:include href="standard-options.xml" xpointer="help" />
      <xi:include href="standard-options.xml" xpointer="version" />
    </variablelist>
  </refsect1>

  <refsect1><title>Kernel command line</title>
    <variablelist class='kernel-commandline-options'>
      <para>Parameters starting with "rd." will be read when
      <command>systemd-udevd</command> is used in an initrd.</para>
      <varlistentry>
        <term><varname>udev.log_priority=</varname></term>
        <term><varname>rd.udev.log_priority=</varname></term>
        <listitem>
          <para>Set the log level.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>udev.children_max=</varname></term>
        <term><varname>rd.udev.children_max=</varname></term>
        <listitem>
          <para>Limit the number of events executed in parallel.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>udev.exec_delay=</varname></term>
        <term><varname>rd.udev.exec_delay=</varname></term>
        <listitem>
          <para>Delay the execution of <varname>RUN</varname> instructions by the given
          number of seconds. This option might be useful when
          debugging system crashes during coldplug caused by loading
          non-working kernel modules.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>udev.event_timeout=</varname></term>
        <term><varname>rd.udev.event_timeout=</varname></term>
        <listitem>
          <para>Wait for events to finish up to the given number
          of seconds. This option might be useful if events are
          terminated due to kernel drivers taking too long to initialize.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>net.ifnames=</varname></term>
        <listitem>
          <para>Network interfaces are renamed to give them predictable names
          when possible. It is enabled by default; specifying 0 disables it.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>net.naming-scheme=</varname></term>
        <listitem>
          <para>Network interfaces are renamed to give them predictable names when possible (unless
          <varname>net.ifnames=0</varname> is specified, see above). The names are derived from various
          device metadata fields. Newer versions of <filename>systemd-udevd.service</filename> take more of
          these fields into account, improving (and thus possibly changing) the names used for the same
          devices. With this kernel command line option it is possible to pick a specific version of this
          algorithm. It expects a naming scheme identifier as argument. Currently the following identifiers
          are known: <literal>v238</literal>, <literal>v239</literal>, <literal>v240</literal> which each
          implement the naming scheme that was the default in the indicated systemd version. In addition,
          <literal>latest</literal> may be used to designate the latest scheme known (to this particular
          version of <filename>systemd-udevd.service</filename>).</para>

          <para>Note that selecting a specific scheme is not sufficient to fully stabilize interface naming:
          the naming is generally derived from driver attributes exposed by the kernel. As the kernel is
          updated, previously missing attributes <filename>systemd-udevd.service</filename> is checking might
          appear, which affects older name derivation algorithms, too.</para>
        </listitem>
      </varlistentry>
    </variablelist>
    <!-- when adding entries here, consider also adding them
         in kernel-command-line.xml -->
 </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>udev.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    </para>
  </refsect1>
</refentry>