man/systemd-udevd.service.xml

   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+ -->
   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 <varname>RUN</varname>
  92           instructions 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_priority=</varname></term>
 147         <term><varname>rd.udev.log_priority=</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 <varname>RUN</varname> instructions 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     </variablelist>
 228     <!-- when adding entries here, consider also adding them in kernel-command-line.xml -->
 229   </refsect1>
 230
 231   <refsect1>
 232     <title>See Also</title>
 233     <para>
 234       <citerefentry><refentrytitle>udev.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 235       <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 236       <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 237     </para>
 238   </refsect1>
 239 </refentry>