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This is useful for distributions, where the stability of interface names should be preseved after an upgrade of systemd. So when some specific release of the distro is made available, systemd defaults to the latest & greatest naming scheme, and subsequent updates set the same default. This default may still be overriden through the kernel and env var options. A special value "latest" is also allowed. Without a specific name, it is harder to verride from meson. In case of 'combo' options, meson reads the default during the initial configuration, and "remembers" this choice. When systemd is updated, old build/ directories could keep the old default, which would be annoying. Hence, "latest" is introduced to make it explicit, yet follow the upstream. This is actually useful for the user too, because it may be used as an override, without having to actually specify a version.
207 lines
8.3 KiB
XML
207 lines
8.3 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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-->
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<refentry id="systemd-udevd.service"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>systemd-udevd.service</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-udevd.service</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-udevd.service</refname>
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<refname>systemd-udevd-control.socket</refname>
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<refname>systemd-udevd-kernel.socket</refname>
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<refname>systemd-udevd</refname>
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<refpurpose>Device event managing daemon</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd-udevd.service</filename></para>
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<para><filename>systemd-udevd-control.socket</filename></para>
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<para><filename>systemd-udevd-kernel.socket</filename></para>
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<cmdsynopsis>
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<command>/usr/lib/systemd/systemd-udevd</command>
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<arg><option>--daemon</option></arg>
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<arg><option>--debug</option></arg>
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<arg><option>--children-max=</option></arg>
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<arg><option>--exec-delay=</option></arg>
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<arg><option>--event-timeout=</option></arg>
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<arg><option>--resolve-names=early|late|never</option></arg>
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<arg><option>--version</option></arg>
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<arg><option>--help</option></arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1><title>Description</title>
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<para><command>systemd-udevd</command> listens to kernel uevents.
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For every event, systemd-udevd executes matching instructions
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specified in udev rules. See <citerefentry>
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<refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum>
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</citerefentry>.</para>
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<para>The behavior of the daemon can be configured using
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<citerefentry><refentrytitle>udev.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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its command line options, environment variables, and on the kernel
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command line, or changed dynamically with <command>udevadm
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control</command>.
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</para>
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</refsect1>
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<refsect1><title>Options</title>
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<variablelist>
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<varlistentry>
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<term><option>-d</option></term>
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<term><option>--daemon</option></term>
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<listitem>
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<para>Detach and run in the background.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-D</option></term>
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<term><option>--debug</option></term>
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<listitem>
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<para>Print debug messages to standard error.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-c=</option></term>
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<term><option>--children-max=</option></term>
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<listitem>
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<para>Limit the number of events executed in parallel.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-e=</option></term>
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<term><option>--exec-delay=</option></term>
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<listitem>
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<para>Delay the execution of <varname>RUN</varname>
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instructions by the given number of seconds. This option
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might be useful when debugging system crashes during
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coldplug caused by loading non-working kernel
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modules.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-t=</option></term>
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<term><option>--event-timeout=</option></term>
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<listitem>
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<para>Set the number of seconds to wait for events to finish. After
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this time, the event will be terminated. The default is 180 seconds.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-N=</option></term>
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<term><option>--resolve-names=</option></term>
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<listitem>
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<para>Specify when systemd-udevd should resolve names of users and groups.
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When set to <option>early</option> (the default), names will be
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resolved when the rules are parsed. When set to
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<option>late</option>, names will be resolved for every event.
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When set to <option>never</option>, names will never be resolved
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and all devices will be owned by root.</para>
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</listitem>
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</varlistentry>
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<xi:include href="standard-options.xml" xpointer="help" />
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<xi:include href="standard-options.xml" xpointer="version" />
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</variablelist>
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</refsect1>
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<refsect1><title>Kernel command line</title>
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<variablelist class='kernel-commandline-options'>
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<para>Parameters starting with "rd." will be read when
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<command>systemd-udevd</command> is used in an initrd.</para>
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<varlistentry>
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<term><varname>udev.log_priority=</varname></term>
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<term><varname>rd.udev.log_priority=</varname></term>
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<listitem>
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<para>Set the log level.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>udev.children_max=</varname></term>
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<term><varname>rd.udev.children_max=</varname></term>
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<listitem>
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<para>Limit the number of events executed in parallel.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>udev.exec_delay=</varname></term>
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<term><varname>rd.udev.exec_delay=</varname></term>
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<listitem>
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<para>Delay the execution of <varname>RUN</varname> instructions by the given
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number of seconds. This option might be useful when
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debugging system crashes during coldplug caused by loading
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non-working kernel modules.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>udev.event_timeout=</varname></term>
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<term><varname>rd.udev.event_timeout=</varname></term>
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<listitem>
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<para>Wait for events to finish up to the given number
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of seconds. This option might be useful if events are
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terminated due to kernel drivers taking too long to initialize.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>net.ifnames=</varname></term>
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<listitem>
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<para>Network interfaces are renamed to give them predictable names
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when possible. It is enabled by default; specifying 0 disables it.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>net.naming-scheme=</varname></term>
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<listitem>
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<para>Network interfaces are renamed to give them predictable names when possible (unless
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<varname>net.ifnames=0</varname> is specified, see above). The names are derived from various
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device metadata fields. Newer versions of <filename>systemd-udevd.service</filename> take more of
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these fields into account, improving (and thus possibly changing) the names used for the same
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devices. With this kernel command line option it is possible to pick a specific version of this
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algorithm. It expects a naming scheme identifier as argument. Currently the following identifiers
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are known: <literal>v238</literal>, <literal>v239</literal>, <literal>v240</literal> which each
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implement the naming scheme that was the default in the indicated systemd version. In addition,
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<literal>latest</literal> may be used to designate the latest scheme known (to this particular
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version of <filename>systemd-udevd.service</filename>).</para>
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<para>Note that selecting a specific scheme is not sufficient to fully stabilize interface naming:
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the naming is generally derived from driver attributes exposed by the kernel. As the kernel is
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updated, previously missing attributes <filename>systemd-udevd.service</filename> is checking might
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appear, which affects older name derivation algorithms, too.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<!-- when adding entries here, consider also adding them
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in kernel-command-line.xml -->
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>udev.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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