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+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<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>
+
+ <xi:include href="version-info.xml" xpointer="v186"/>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-D</option></term>
+ <term><option>--debug</option></term>
+ <listitem>
+ <para>Print debug messages to standard error.</para>
+
+ <xi:include href="version-info.xml" xpointer="v186"/>
+ </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>
+
+ <xi:include href="version-info.xml" xpointer="v186"/>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-e</option></term>
+ <term><option>--exec-delay=</option></term>
+ <listitem>
+ <para>Delay the execution of each <varname>RUN{<replaceable>program</replaceable>}</varname>
+ parameter 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>
+
+ <xi:include href="version-info.xml" xpointer="v186"/>
+ </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>
+
+ <xi:include href="version-info.xml" xpointer="v216"/>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-s</option></term>
+ <term><option>--timeout-signal=</option></term>
+ <listitem>
+ <para>Set the signal which <filename>systemd-udevd</filename> will send to
+ forked off processes after reaching event timeout. The setting can be overridden
+ at boot time with the kernel command line option
+ <varname>udev.timeout_signal=</varname>. Setting to <constant>SIGABRT</constant>
+ may be helpful in order to debug worker timeouts. Defaults to
+ <constant>SIGKILL</constant>. Note that setting the option on the command line
+ overrides the setting from the configuration file.
+ </para>
+
+ <xi:include href="version-info.xml" xpointer="v246"/>
+ </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>
+
+ <xi:include href="version-info.xml" xpointer="v186"/>
+ </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 prefixed with "rd." will be read when <command>systemd-udevd</command> is used in an
+ initrd, those without will be processed both in the initrd and on the host.</para>
+ <varlistentry>
+ <term><varname>udev.log_level=</varname></term>
+ <term><varname>rd.udev.log_level=</varname></term>
+ <listitem>
+ <para>Set the log level.</para>
+
+ <xi:include href="version-info.xml" xpointer="v247"/>
+ </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>
+
+ <xi:include href="version-info.xml" xpointer="v186"/>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>udev.exec_delay=</varname></term>
+ <term><varname>rd.udev.exec_delay=</varname></term>
+ <listitem>
+ <para>Delay the execution of each <varname>RUN{<replaceable>program</replaceable>}</varname> parameter 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>
+
+ <xi:include href="version-info.xml" xpointer="v186"/>
+ </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>
+
+ <xi:include href="version-info.xml" xpointer="v216"/>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>udev.timeout_signal=</varname></term>
+ <term><varname>rd.udev.timeout_signal=</varname></term>
+ <listitem>
+ <para>Specifies a signal that <filename>systemd-udevd</filename> will send to
+ workers on timeout. Note that kernel command line option overrides both the
+ setting in the configuration file and the one on the program command line.</para>
+
+ <xi:include href="version-info.xml" xpointer="v246"/>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>udev.blockdev_read_only</varname></term>
+ <term><varname>rd.udev.blockdev_read_only</varname></term>
+ <listitem>
+ <para>If specified, mark all physical block devices read-only as they appear. Synthetic block
+ devices (such as loopback block devices or device mapper devices) are left as they are. This is
+ useful to guarantee that the contents of physical block devices remains unmodified during runtime,
+ for example to implement fully stateless systems, for testing or for recovery situations where
+ corrupted file systems shall not be corrupted further through accidental modification.</para>
+
+ <para>A block device may be marked writable again by issuing the <command>blockdev
+ --setrw</command> command, see <citerefentry
+ project='man-pages'><refentrytitle>blockdev</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for details.</para>
+
+ <xi:include href="version-info.xml" xpointer="v246"/>
+ </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>
+
+ <xi:include href="version-info.xml" xpointer="v199"/>
+ </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). With this kernel command line option it
+ is possible to pick a specific version of this algorithm and override the default chosen at
+ compilation time. Expects one of the naming scheme identifiers listed in
+ <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ or <literal>latest</literal> to select 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>
+
+ <xi:include href="version-info.xml" xpointer="v240"/>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><varname>net.ifname-policy=<replaceable>policy1</replaceable>[,<replaceable>policy2</replaceable>,…][,<replaceable>MAC</replaceable>]</varname></term>
+ <listitem>
+ <para>Specifies naming policies applied when renaming network interfaces. Takes a list of
+ policies and an optional MAC address separated with comma. Each policy value must be one of
+ the policies understood by the <varname>NamePolicy=</varname> setting in .link files, e.g.
+ <literal>onboard</literal> or <literal>path</literal>. See
+ <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for more details. When the MAC address is specified, the policies are applied to the
+ interface which has the address. When no MAC address is specified, the policies are applied
+ to all interfaces. This kernel command line argument can be specified multiple times.</para>
+
+ <para>This argument is not directly read by <command>systemd-udevd</command>, but is instead
+ converted to a .link file by
+ <citerefentry><refentrytitle>systemd-network-generator.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+ For this argument to take effect, <filename>systemd-network-generator.service</filename> must be
+ enabled.</para>
+
+ <para>Example:
+ <programlisting>net.ifname-policy=keep,kernel,path,slot,onboard,01:23:45:67:89:ab
+net.ifname-policy=keep,kernel,path,slot,onboard,mac</programlisting>
+ This is mostly equivalent to creating the following .link files:
+ <programlisting># 91-name-policy-with-mac.link
+[Match]
+MACAddress=01:23:45:67:89:ab
+
+[Link]
+NamePolicy=keep kernel path slot onboard
+AlternativeNamePolicy=path slot onboard</programlisting>
+ and
+ <programlisting># 92-name-policy-for-all.link
+[Match]
+OriginalName=*
+
+[Link]
+NamePolicy=keep kernel path slot onboard mac
+AlternativeNamePolicy=path slot onboard mac</programlisting>
+ </para>
+
+ <xi:include href="version-info.xml" xpointer="v250"/>
+ </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>