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<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 standard error.</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 <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>--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 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>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>

</variablelist>

<!-- when adding entries here, consider also adding them

</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>