man/systemd-udevd.service.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.5/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
  69         <xi:include href="version-info.xml" xpointer="v186"/>
  70         </listitem>
  71       </varlistentry>
  72
  73       <varlistentry>
  74         <term><option>-D</option></term>
  75         <term><option>--debug</option></term>
  76         <listitem>
  77           <para>Print debug messages to standard error.</para>
  78
  79         <xi:include href="version-info.xml" xpointer="v186"/>
  80         </listitem>
  81       </varlistentry>
  82
  83       <varlistentry>
  84         <term><option>-c</option></term>
  85         <term><option>--children-max=</option></term>
  86         <listitem>
  87           <para>Limit the number of events executed in parallel.</para>
  88
  89         <xi:include href="version-info.xml" xpointer="v186"/>
  90         </listitem>
  91       </varlistentry>
  92
  93       <varlistentry>
  94         <term><option>-e</option></term>
  95         <term><option>--exec-delay=</option></term>
  96         <listitem>
  97           <para>Delay the execution of each <varname>RUN{<replaceable>program</replaceable>}</varname>
  98           parameter by the given number of seconds. This option
  99           might be useful when debugging system crashes during
 100           coldplug caused by loading non-working kernel
 101           modules.</para>
 102
 103         <xi:include href="version-info.xml" xpointer="v186"/>
 104         </listitem>
 105       </varlistentry>
 106
 107       <varlistentry>
 108         <term><option>-t</option></term>
 109         <term><option>--event-timeout=</option></term>
 110         <listitem>
 111           <para>Set the number of seconds to wait for events to finish. After
 112           this time, the event will be terminated. The default is 180 seconds.</para>
 113
 114           <xi:include href="version-info.xml" xpointer="v216"/>
 115         </listitem>
 116       </varlistentry>
 117
 118       <varlistentry>
 119         <term><option>-s</option></term>
 120         <term><option>--timeout-signal=</option></term>
 121         <listitem>
 122           <para>Set the signal which <filename>systemd-udevd</filename> will send to
 123           forked off processes after reaching event timeout. The setting can be overridden
 124           at boot time with the kernel command line option
 125           <varname>udev.timeout_signal=</varname>. Setting to <constant>SIGABRT</constant>
 126           may be helpful in order to debug worker timeouts. Defaults to
 127           <constant>SIGKILL</constant>. Note that setting the option on the command line
 128           overrides the setting from the configuration file.
 129           </para>
 130
 131         <xi:include href="version-info.xml" xpointer="v246"/>
 132         </listitem>
 133       </varlistentry>
 134
 135       <varlistentry>
 136         <term><option>-N</option></term>
 137         <term><option>--resolve-names=</option></term>
 138         <listitem>
 139           <para>Specify when systemd-udevd should resolve names of users and groups.
 140           When set to <option>early</option> (the default), names will be
 141           resolved when the rules are parsed.  When set to
 142           <option>late</option>, names will be resolved for every event.
 143           When set to <option>never</option>, names will never be resolved
 144           and all devices will be owned by root.</para>
 145
 146           <xi:include href="version-info.xml" xpointer="v186"/>
 147         </listitem>
 148       </varlistentry>
 149
 150       <xi:include href="standard-options.xml" xpointer="help" />
 151       <xi:include href="standard-options.xml" xpointer="version" />
 152     </variablelist>
 153   </refsect1>
 154
 155   <refsect1><title>Kernel command line</title>
 156     <variablelist class='kernel-commandline-options'>
 157       <para>Parameters prefixed with "rd." will be read when <command>systemd-udevd</command> is used in an
 158       initrd, those without will be processed both in the initrd and on the host.</para>
 159       <varlistentry>
 160         <term><varname>udev.log_level=</varname></term>
 161         <term><varname>rd.udev.log_level=</varname></term>
 162         <listitem>
 163           <para>Set the log level.</para>
 164
 165         <xi:include href="version-info.xml" xpointer="v247"/>
 166         </listitem>
 167       </varlistentry>
 168       <varlistentry>
 169         <term><varname>udev.children_max=</varname></term>
 170         <term><varname>rd.udev.children_max=</varname></term>
 171         <listitem>
 172           <para>Limit the number of events executed in parallel.</para>
 173
 174         <xi:include href="version-info.xml" xpointer="v186"/>
 175         </listitem>
 176       </varlistentry>
 177       <varlistentry>
 178         <term><varname>udev.exec_delay=</varname></term>
 179         <term><varname>rd.udev.exec_delay=</varname></term>
 180         <listitem>
 181           <para>Delay the execution of each <varname>RUN{<replaceable>program</replaceable>}</varname> parameter by the given
 182           number of seconds. This option might be useful when
 183           debugging system crashes during coldplug caused by loading
 184           non-working kernel modules.</para>
 185
 186         <xi:include href="version-info.xml" xpointer="v186"/>
 187         </listitem>
 188       </varlistentry>
 189       <varlistentry>
 190         <term><varname>udev.event_timeout=</varname></term>
 191         <term><varname>rd.udev.event_timeout=</varname></term>
 192         <listitem>
 193           <para>Wait for events to finish up to the given number
 194           of seconds. This option might be useful if events are
 195           terminated due to kernel drivers taking too long to initialize.</para>
 196
 197           <xi:include href="version-info.xml" xpointer="v216"/>
 198         </listitem>
 199       </varlistentry>
 200       <varlistentry>
 201         <term><varname>udev.timeout_signal=</varname></term>
 202         <term><varname>rd.udev.timeout_signal=</varname></term>
 203         <listitem>
 204           <para>Specifies a signal that <filename>systemd-udevd</filename> will send to
 205           workers on timeout. Note that kernel command line option overrides both the
 206           setting in the configuration file and the one on the program command line.</para>
 207
 208         <xi:include href="version-info.xml" xpointer="v246"/>
 209         </listitem>
 210       </varlistentry>
 211       <varlistentry>
 212         <term><varname>udev.blockdev_read_only</varname></term>
 213         <term><varname>rd.udev.blockdev_read_only</varname></term>
 214         <listitem>
 215           <para>If specified, mark all physical block devices read-only as they appear. Synthetic block
 216           devices (such as loopback block devices or device mapper devices) are left as they are. This is
 217           useful to guarantee that the contents of physical block devices remains unmodified during runtime,
 218           for example to implement fully stateless systems, for testing or for recovery situations where
 219           corrupted file systems shall not be corrupted further through accidental modification.</para>
 220
 221           <para>A block device may be marked writable again by issuing the <command>blockdev
 222           --setrw</command> command, see <citerefentry
 223           project='man-pages'><refentrytitle>blockdev</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 224           for details.</para>
 225
 226           <xi:include href="version-info.xml" xpointer="v246"/>
 227         </listitem>
 228       </varlistentry>
 229       <varlistentry>
 230         <term><varname>net.ifnames=</varname></term>
 231         <listitem>
 232           <para>Network interfaces are renamed to give them predictable names
 233           when possible. It is enabled by default; specifying 0 disables it.</para>
 234
 235           <xi:include href="version-info.xml" xpointer="v199"/>
 236         </listitem>
 237       </varlistentry>
 238       <varlistentry>
 239         <term><varname>net.naming_scheme=</varname></term>
 240         <listitem>
 241           <para>Network interfaces are renamed to give them predictable names when possible (unless
 242           <varname>net.ifnames=0</varname> is specified, see above). With this kernel command line option it
 243           is possible to pick a specific version of this algorithm and override the default chosen at
 244           compilation time. Expects one of the naming scheme identifiers listed in
 245           <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 246           or <literal>latest</literal> to select the latest scheme known (to this particular version of
 247           <filename>systemd-udevd.service</filename>).</para>
 248
 249           <para>Note that selecting a specific scheme is not sufficient to fully stabilize interface naming:
 250           the naming is generally derived from driver attributes exposed by the kernel. As the kernel is
 251           updated, previously missing attributes <filename>systemd-udevd.service</filename> is checking might
 252           appear, which affects older name derivation algorithms, too.</para>
 253
 254           <xi:include href="version-info.xml" xpointer="v240"/>
 255         </listitem>
 256       </varlistentry>
 257       <varlistentry>
 258         <term><varname>net.ifname_policy=<replaceable>policy1</replaceable>[,<replaceable>policy2</replaceable>,…][,<replaceable>MAC</replaceable>]</varname></term>
 259         <listitem>
 260           <para>Specifies naming policies applied when renaming network interfaces. Takes a list of
 261           policies and an optional MAC address separated with comma. Each policy value must be one of
 262           the policies understood by the <varname>NamePolicy=</varname> setting in .link files, e.g.
 263           <literal>onboard</literal> or <literal>path</literal>. See
 264           <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 265           for more details. When the MAC address is specified, the policies are applied to the
 266           interface which has the address. When no MAC address is specified, the policies are applied
 267           to all interfaces. This kernel command line argument can be specified multiple times.</para>
 268
 269           <para>This argument is not directly read by <command>systemd-udevd</command>, but is instead
 270           converted to a .link file by
 271           <citerefentry><refentrytitle>systemd-network-generator.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 272           For this argument to take effect, <filename>systemd-network-generator.service</filename> must be
 273           enabled.</para>
 274
 275           <para>Example:
 276           <programlisting>net.ifname_policy=keep,kernel,path,slot,onboard,01:23:45:67:89:ab
 277 net.ifname_policy=keep,kernel,path,slot,onboard,mac</programlisting>
 278           This is mostly equivalent to creating the following .link files:
 279           <programlisting># 91-name-policy-with-mac.link
 280 [Match]
 281 MACAddress=01:23:45:67:89:ab
 282
 283 [Link]
 284 NamePolicy=keep kernel path slot onboard
 285 AlternativeNamePolicy=path slot onboard</programlisting>
 286           and
 287           <programlisting># 92-name-policy-for-all.link
 288 [Match]
 289 OriginalName=*
 290
 291 [Link]
 292 NamePolicy=keep kernel path slot onboard mac
 293 AlternativeNamePolicy=path slot onboard mac</programlisting>
 294           </para>
 295
 296           <xi:include href="version-info.xml" xpointer="v250"/>
 297         </listitem>
 298       </varlistentry>
 299     </variablelist>
 300     <!-- when adding entries here, consider also adding them in kernel-command-line.xml -->
 301   </refsect1>
 302
 303   <refsect1>
 304     <title>See Also</title>
 305     <para><simplelist type="inline">
 306       <member><citerefentry><refentrytitle>udev.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 307       <member><citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
 308       <member><citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 309     </simplelist></para>
 310   </refsect1>
 311 </refentry>