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<?xml version='1.0'?>
<?xml-stylesheet type="text/xsl" href="http://docbook.sourceforge.net/release/xsl/current/xhtml/docbook.xsl"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<refentry id="systemd-udevd.service">
<refentryinfo>
<title>systemd-udevd.service</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Kay</firstname>
<surname>Sievers</surname>
<email>kay@vrfy.org</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-udevd.service</refentrytitle>
<manvolnum>8</manvolnum>
<refmiscinfo class="version"></refmiscinfo>
</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>--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 running daemon can be changed with
<command>udevadm control</command>.</para>
</refsect1>
<refsect1><title>Options</title>
<variablelist>
<varlistentry>
<term><option>--daemon</option></term>
<listitem>
<para>Detach and run in the background.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--debug</option></term>
<listitem>
<para>Print debug messages to stderr.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--children-max=</option></term>
<listitem>
<para>Limit the number of events executed in parallel.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--exec-delay=</option></term>
<listitem>
<para>Delay the execution of RUN instruction 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>--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>
<varlistentry>
<term><option>--version</option></term>
<listitem>
<para>Print version number.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--help</option></term>
<listitem>
<para>Print help text.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1><title>Environment</title>
<variablelist class='environment-variables'>
<varlistentry>
<term><varname>$UDEV_LOG=</varname></term>
<listitem>
<para>Set the logging priority.</para>
</listitem>
</varlistentry>
</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 logging priority.</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 RUN instruction 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>
</variablelist>
</refsect1>
<refsect1><title>Configuration file</title>
<para>udev expects its main configuration file at <filename>/etc/udev/udev.conf</filename>.
It consists of a set of variables allowing the user to override default udev values. All
empty lines or lines beginning with '#' are ignored. The following variables can be
set:</para>
<variablelist>
<varlistentry>
<term><varname>udev_log</varname></term>
<listitem>
<para>The logging priority. Valid values are the numerical syslog priorities
or their textual representations: <option>err</option>, <option>info</option>
and <option>debug</option>.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>See Also</title>
<para><citerefentry>
<refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum>
</citerefentry>, <citerefentry>
<refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
</citerefentry></para>
</refsect1>
</refentry>
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