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-or-later -->
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 each <varname>RUN{<replaceable>program</replaceable>}</varname>
92          parameter 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>-s</option></term>
110        <term><option>--timeout-signal=</option></term>
111        <listitem>
112          <para>Set the signal which <filename>systemd-udevd</filename> will send to
113          forked off processes after reaching event timeout. The setting can be overridden
114          at boot time with the kernel command line option
115          <varname>udev.timeout_signal=</varname>. Setting to <constant>SIGABRT</constant>
116          may be helpful in order to debug worker timeouts. Defaults to
117          <constant>SIGKILL</constant>. Note that setting the option on the command line
118          overrides the setting from the configuration file.
119          </para>
120        </listitem>
121      </varlistentry>
122
123      <varlistentry>
124        <term><option>-N</option></term>
125        <term><option>--resolve-names=</option></term>
126        <listitem>
127          <para>Specify when systemd-udevd should resolve names of users and groups.
128          When set to <option>early</option> (the default), names will be
129          resolved when the rules are parsed.  When set to
130          <option>late</option>, names will be resolved for every event.
131          When set to <option>never</option>, names will never be resolved
132          and all devices will be owned by root.</para>
133        </listitem>
134      </varlistentry>
135
136      <xi:include href="standard-options.xml" xpointer="help" />
137      <xi:include href="standard-options.xml" xpointer="version" />
138    </variablelist>
139  </refsect1>
140
141  <refsect1><title>Kernel command line</title>
142    <variablelist class='kernel-commandline-options'>
143      <para>Parameters prefixed with "rd." will be read when <command>systemd-udevd</command> is used in an
144      initrd, those without will be processed both in the initrd and on the host.</para>
145      <varlistentry>
146        <term><varname>udev.log_level=</varname></term>
147        <term><varname>rd.udev.log_level=</varname></term>
148        <listitem>
149          <para>Set the log level.</para>
150        </listitem>
151      </varlistentry>
152      <varlistentry>
153        <term><varname>udev.children_max=</varname></term>
154        <term><varname>rd.udev.children_max=</varname></term>
155        <listitem>
156          <para>Limit the number of events executed in parallel.</para>
157        </listitem>
158      </varlistentry>
159      <varlistentry>
160        <term><varname>udev.exec_delay=</varname></term>
161        <term><varname>rd.udev.exec_delay=</varname></term>
162        <listitem>
163          <para>Delay the execution of each <varname>RUN{<replaceable>program</replaceable>}</varname> parameter by the given
164          number of seconds. This option might be useful when
165          debugging system crashes during coldplug caused by loading
166          non-working kernel modules.</para>
167        </listitem>
168      </varlistentry>
169      <varlistentry>
170        <term><varname>udev.event_timeout=</varname></term>
171        <term><varname>rd.udev.event_timeout=</varname></term>
172        <listitem>
173          <para>Wait for events to finish up to the given number
174          of seconds. This option might be useful if events are
175          terminated due to kernel drivers taking too long to initialize.</para>
176        </listitem>
177      </varlistentry>
178      <varlistentry>
179        <term><varname>udev.timeout_signal=</varname></term>
180        <term><varname>rd.udev.timeout_signal=</varname></term>
181        <listitem>
182          <para>Specifies a signal that <filename>systemd-udevd</filename> will send to
183          workers on timeout. Note that kernel command line option overrides both the
184          setting in the configuration file and the one on the program command line.</para>
185        </listitem>
186      </varlistentry>
187      <varlistentry>
188        <term><varname>udev.blockdev_read_only</varname></term>
189        <term><varname>rd.udev.blockdev_read_only</varname></term>
190        <listitem>
191          <para>If specified, mark all physical block devices read-only as they appear. Synthetic block
192          devices (such as loopback block devices or device mapper devices) are left as they are. This is
193          useful to guarantee that the contents of physical block devices remains unmodified during runtime,
194          for example to implement fully stateless systems, for testing or for recovery situations where
195          corrupted file systems shall not be corrupted further through accidental modification.</para>
196
197          <para>A block device may be marked writable again by issuing the <command>blockdev
198          --setrw</command> command, see <citerefentry
199          project='man-pages'><refentrytitle>blockdev</refentrytitle><manvolnum>8</manvolnum></citerefentry>
200          for details.</para>
201        </listitem>
202      </varlistentry>
203      <varlistentry>
204        <term><varname>net.ifnames=</varname></term>
205        <listitem>
206          <para>Network interfaces are renamed to give them predictable names
207          when possible. It is enabled by default; specifying 0 disables it.</para>
208        </listitem>
209      </varlistentry>
210      <varlistentry>
211        <term><varname>net.naming-scheme=</varname></term>
212        <listitem>
213          <para>Network interfaces are renamed to give them predictable names when possible (unless
214          <varname>net.ifnames=0</varname> is specified, see above). With this kernel command line option it
215          is possible to pick a specific version of this algorithm and override the default chosen at
216          compilation time. Expects one of the naming scheme identifiers listed in
217          <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
218          or <literal>latest</literal> to select the latest scheme known (to this particular version of
219          <filename>systemd-udevd.service</filename>).</para>
220
221          <para>Note that selecting a specific scheme is not sufficient to fully stabilize interface naming:
222          the naming is generally derived from driver attributes exposed by the kernel. As the kernel is
223          updated, previously missing attributes <filename>systemd-udevd.service</filename> is checking might
224          appear, which affects older name derivation algorithms, too.</para>
225        </listitem>
226      </varlistentry>
227      <varlistentry>
228        <term><varname>net.ifname-policy=<replaceable>policy1</replaceable>[,<replaceable>policy2</replaceable>,…][,<replaceable>MAC</replaceable>]</varname></term>
229        <listitem>
230          <para>Specifies naming policies applied when renaming network interfaces. Takes a list of
231          policies and an optional MAC address separated with comma. Each policy value must be one of
232          the policies understood by the <varname>NamePolicy=</varname> setting in .link files, e.g.
233          <literal>onboard</literal> or <literal>path</literal>. See
234          <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>
235          for more details. When the MAC address is specified, the policies are applied to the
236          interface which has the address. When no MAC address is specified, the policies are applied
237          to all interfaces. This kernel command line argument can be specified multiple times.</para>
238
239          <para>This argument is not directly read by <command>systemd-udevd</command>, but is instead
240          converted to a .link file by
241          <citerefentry><refentrytitle>systemd-network-generator.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
242          For this argument to take effect, <filename>systemd-network-generator.service</filename> must be
243          enabled.</para>
244
245          <para>Example:
246          <programlisting>net.ifname-policy=keep,kernel,path,slot,onboard,01:23:45:67:89:ab
247net.ifname-policy=keep,kernel,path,slot,onboard,mac</programlisting>
248          This is mostly equivalent to creating the following .link files:
249          <programlisting># 91-name-policy-with-mac.link
250[Match]
251MACAddress=01:23:45:67:89:ab
252
253[Link]
254NamePolicy=keep kernel path slot onboard
255AlternativeNamePolicy=path slot onboard</programlisting>
256          and
257          <programlisting># 92-name-policy-for-all.link
258[Match]
259OriginalName=*
260
261[Link]
262NamePolicy=keep kernel path slot onboard mac
263AlternativeNamePolicy=path slot onboard mac</programlisting>
264          </para>
265        </listitem>
266      </varlistentry>
267    </variablelist>
268    <!-- when adding entries here, consider also adding them in kernel-command-line.xml -->
269  </refsect1>
270
271  <refsect1>
272    <title>See Also</title>
273    <para>
274      <citerefentry><refentrytitle>udev.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
275      <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
276      <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
277    </para>
278  </refsect1>
279</refentry>
280