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857 lines
38 KiB
XML
857 lines
38 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//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-or-later
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Copyright © 2014 Jason St. John
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-->
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<refentry id="udev">
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<refentryinfo>
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<title>udev</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>udev</refentrytitle>
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<manvolnum>7</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>udev</refname>
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<refpurpose>Dynamic device management</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<para>udev supplies the system software with device events, manages permissions
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of device nodes and may create additional symlinks in the <filename>/dev/</filename>
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directory, or renames network interfaces. The kernel usually just assigns unpredictable
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device names based on the order of discovery. Meaningful symlinks or network device
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names provide a way to reliably identify devices based on their properties or
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current configuration.</para>
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<para>The udev daemon, <citerefentry><refentrytitle>systemd-udevd.service</refentrytitle>
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<manvolnum>8</manvolnum></citerefentry>, receives device uevents directly from
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the kernel whenever a device is added or removed from the system, or it changes its
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state. When udev receives a device event, it matches its configured set of rules
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against various device attributes to identify the device. Rules that match may
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provide additional device information to be stored in the udev database or
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to be used to create meaningful symlink names.</para>
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<para>All device information udev processes is stored in the udev database and
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sent out to possible event subscribers. Access to all stored data and the event
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sources is provided by the library libudev.</para>
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</refsect1>
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<refsect1>
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<title>Rules Files</title>
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<para>The udev rules are read from the files located in the system rules directories
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<filename>/usr/lib/udev/rules.d</filename> and <filename>/usr/local/lib/udev/rules.d</filename>, the
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volatile runtime directory <filename>/run/udev/rules.d</filename> and the local administration
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directory <filename>/etc/udev/rules.d</filename>. All rules files are collectively sorted and
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processed in lexical order, regardless of the directories in which they live. However, files with
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identical filenames replace each other. Files in <filename>/etc/</filename> have the highest priority,
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files in <filename>/run/</filename> take precedence over files with the same name under
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<filename>/usr/</filename>. This can be used to override a system-supplied rules file with a local
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file if needed; a symlink in <filename>/etc/</filename> with the same name as a rules file in
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<filename>/usr/lib/</filename>, pointing to <filename>/dev/null</filename>, disables the rules file
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entirely. Rule files must have the extension <filename>.rules</filename>; other extensions are
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ignored.</para>
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<para>Every line in the rules file contains at least one key-value pair.
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Except for empty lines or lines beginning with <literal>#</literal>, which are ignored.
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There are two kinds of keys: match and assignment.
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If all match keys match against their values, the rule gets applied and the
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assignment keys get the specified values assigned.</para>
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<para>A matching rule may rename a network interface, add symlinks
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pointing to the device node, or run a specified program as part of
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the event handling.</para>
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<para>A rule consists of a comma-separated list of one or more key-operator-value expressions.
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Each expression has a distinct effect, depending on the key and operator used.</para>
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<refsect2>
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<title>Operators</title>
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<variablelist>
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<varlistentry>
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<term><literal>==</literal></term>
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<listitem>
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<para>Compare for equality. (The specified key has the specified value.)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>!=</literal></term>
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<listitem>
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<para>Compare for inequality. (The specified key doesn't have the specified value, or the
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specified key is not present at all.)
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>=</literal></term>
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<listitem>
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<para>Assign a value to a key. Keys that represent a list are reset
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and only this single value is assigned.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>+=</literal></term>
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<listitem>
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<para>Add the value to a key that holds a list of entries.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>-=</literal></term>
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<listitem>
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<para>Remove the value from a key that holds a list of entries.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>:=</literal></term>
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<listitem>
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<para>Assign a value to a key finally; disallow any later changes.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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<refsect2>
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<title>Values</title>
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<para>Values are written as double quoted strings, such as ("string").
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To include a quotation mark (") in the value, precede it by a backslash (\").
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Any other occurrences of a backslash followed by a character are not unescaped.
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That is, "\t\n" is treated as four characters:
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backslash, lowercase t, backslash, lowercase n.</para>
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<para>The string can be prefixed with a lowercase e (e"string\n") to mark the string as
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<ulink url="https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences">C-style escaped</ulink>.
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For example, e"string\n" is parsed as 7 characters: 6 lowercase letters and a newline.
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This can be useful for writing special characters when a kernel driver requires them.</para>
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<para>Please note that <constant>NUL</constant> is not allowed in either string variant.</para>
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</refsect2>
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<refsect2>
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<title>Keys</title>
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<para>The following key names can be used to match against device properties.
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Some of the keys also match against properties of the parent devices in sysfs,
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not only the device that has generated the event. If multiple keys that match
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a parent device are specified in a single rule, all these keys must match at
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one and the same parent device.</para>
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<variablelist class='udev-directives'>
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<varlistentry>
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<term><varname>ACTION</varname></term>
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<listitem>
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<para>Match the name of the event action.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>DEVPATH</varname></term>
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<listitem>
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<para>Match the devpath of the event device.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>KERNEL</varname></term>
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<listitem>
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<para>Match the name of the event device.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>KERNELS</varname></term>
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<listitem>
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<para>Search the devpath upwards for a matching device name.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>NAME</varname></term>
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<listitem>
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<para>Match the name of a network interface. It can be used once the
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NAME key has been set in one of the preceding rules.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SYMLINK</varname></term>
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<listitem>
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<para>Match the name of a symlink targeting the node. It can
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be used once a SYMLINK key has been set in one of the preceding
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rules. There may be multiple symlinks; only one needs to match.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SUBSYSTEM</varname></term>
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<listitem>
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<para>Match the subsystem of the event device.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SUBSYSTEMS</varname></term>
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<listitem>
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<para>Search the devpath upwards for a matching device subsystem name.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>DRIVER</varname></term>
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<listitem>
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<para>Match the driver name of the event device. Only set this key for devices
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which are bound to a driver at the time the event is generated.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>DRIVERS</varname></term>
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<listitem>
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<para>Search the devpath upwards for a matching device driver name.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ATTR{<replaceable>filename</replaceable>}</varname></term>
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<listitem>
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<para>Match sysfs attribute value of the event device.</para>
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<para>Trailing whitespace in the attribute values is ignored unless the specified match value
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itself contains trailing whitespace.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ATTRS{<replaceable>filename</replaceable>}</varname></term>
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<listitem>
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<para>Search the devpath upwards for a device with matching sysfs attribute values. If
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multiple <varname>ATTRS</varname> matches are specified, all of them must match on the same
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device.</para>
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<para>Trailing whitespace in the attribute values is ignored unless the specified match value
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itself contains trailing whitespace.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SYSCTL{<replaceable>kernel parameter</replaceable>}</varname></term>
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<listitem>
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<para>Match a kernel parameter value.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ENV{<replaceable>key</replaceable>}</varname></term>
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<listitem>
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<para>Match against a device property value.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>CONST{<replaceable>key</replaceable>}</varname></term>
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<listitem>
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<para>Match against a system-wide constant. Supported keys are:</para>
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<variablelist>
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<varlistentry>
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<term><literal>arch</literal></term>
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<listitem>
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<para>System's architecture. See <option>ConditionArchitecture=</option> in
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for possible values.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>virt</literal></term>
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<listitem>
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<para>System's virtualization environment. See
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<citerefentry><refentrytitle>systemd-detect-virt</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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for possible values.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>Unknown keys will never match.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TAG</varname></term>
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<listitem>
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<para>Match against a device tag.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TAGS</varname></term>
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<listitem>
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<para>Search the devpath upwards for a device with matching tag.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TEST{<replaceable>octal mode mask</replaceable>}</varname></term>
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<listitem>
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<para>Test the existence of a file. An octal mode mask can be specified
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if needed.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>PROGRAM</varname></term>
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<listitem>
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<para>Execute a program to determine whether there is a match; the key is true if the program
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returns successfully. The device properties are made available to the executed program in the
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environment. The program's standard output is available in the <varname>RESULT</varname>
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key.</para>
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<para>This can only be used for very short-running foreground tasks. For details, see
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<varname>RUN</varname>.</para>
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<para>Note that multiple <varname>PROGRAM</varname> keys may be specified in one rule, and
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<literal>=</literal>, <literal>:=</literal>, and <literal>+=</literal> have the same effect as
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<literal>==</literal>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>RESULT</varname></term>
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<listitem>
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<para>Match the returned string of the last <varname>PROGRAM</varname> call.
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This key can be used in the same or in any later rule after a
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<varname>PROGRAM</varname> call.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>Most of the fields support shell glob pattern matching and
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alternate patterns. The following special characters are supported:</para>
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<variablelist>
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<varlistentry>
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<term><literal>*</literal></term>
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<listitem>
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<para>Matches zero or more characters.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>?</literal></term>
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<listitem>
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<para>Matches any single character.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>[]</literal></term>
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<listitem>
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<para>Matches any single character specified within the brackets. For
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example, the pattern string <literal>tty[SR]</literal>
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would match either <literal>ttyS</literal> or <literal>ttyR</literal>.
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Ranges are also supported via the <literal>-</literal> character.
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For example, to match on the range of all digits, the pattern
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<literal>[0-9]</literal> could be used. If the first character
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following the <literal>[</literal> is a <literal>!</literal>,
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any characters not enclosed are matched.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>|</literal></term>
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<listitem>
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<para>Separates alternative patterns. For example, the pattern string
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<literal>abc|x*</literal> would match either <literal>abc</literal>
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or <literal>x*</literal>.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>The following keys can get values assigned:</para>
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<variablelist class='udev-directives'>
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<varlistentry>
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<term><varname>NAME</varname></term>
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<listitem>
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<para>The name to use for a network interface. See
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<citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for a higher-level mechanism for setting the interface name.
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The name of a device node cannot be changed by udev, only additional
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symlinks can be created.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SYMLINK</varname></term>
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<listitem>
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<para>The name of a symlink targeting the node. Every matching rule adds
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this value to the list of symlinks to be created.</para>
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<para>The set of characters to name a symlink is limited. Allowed
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characters are <literal>0-9A-Za-z#+-.:=@_/</literal>, valid UTF-8 character
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sequences, and <literal>\x00</literal> hex encoding. All other
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characters are replaced by a <literal>_</literal> character.</para>
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<para>Multiple symlinks may be specified by separating the names by the
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space character. In case multiple devices claim the same name, the link
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always points to the device with the highest link_priority. If the current
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device goes away, the links are re-evaluated and the device with the
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next highest link_priority becomes the owner of the link. If no
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link_priority is specified, the order of the devices (and which one of
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them owns the link) is undefined.</para>
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<para>Symlink names must never conflict with the kernel's default device
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node names, as that would result in unpredictable behavior.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>OWNER</varname>, <varname>GROUP</varname>, <varname>MODE</varname></term>
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<listitem>
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<para>The permissions for the device node. Every specified value overrides
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the compiled-in default value.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SECLABEL{<replaceable>module</replaceable>}</varname></term>
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<listitem>
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<para>Applies the specified Linux Security Module label to the device node.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ATTR{<replaceable>key</replaceable>}</varname></term>
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<listitem>
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<para>The value that should be written to a sysfs attribute of the
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event device.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SYSCTL{<replaceable>kernel parameter</replaceable>}</varname></term>
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<listitem>
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<para>The value that should be written to kernel parameter.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ENV{<replaceable>key</replaceable>}</varname></term>
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<listitem>
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<para>Set a device property value. Property names with a leading <literal>.</literal>
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are neither stored in the database nor exported to events or
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external tools (run by, for example, the <varname>PROGRAM</varname>
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match key).</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TAG</varname></term>
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<listitem>
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<para>Attach a tag to a device. This is used to filter events for users
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of libudev's monitor functionality, or to enumerate a group of tagged
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devices. The implementation can only work efficiently if only a few
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tags are attached to a device. It is only meant to be used in
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contexts with specific device filter requirements, and not as a
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general-purpose flag. Excessive use might result in inefficient event
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handling.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>RUN{<replaceable>type</replaceable>}</varname></term>
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<listitem>
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<para>Specify a program to be executed after processing of all the rules for the event. With
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<literal>+=</literal>, this invocation is added to the list, and with <literal>=</literal> or
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<literal>:=</literal>, it replaces any previous contents of the list. Please note that both
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<literal>program</literal> and <literal>builtin</literal> types described below share a common
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list, so clearing the list with <literal>:=</literal> and <literal>=</literal> affects both
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types.</para>
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<para><replaceable>type</replaceable> may be:</para>
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<variablelist>
|
|
<varlistentry>
|
|
<term><literal>program</literal></term>
|
|
<listitem>
|
|
<para>Execute an external program specified as the assigned
|
|
value. If no absolute path is given, the program is expected
|
|
to live in <filename>/usr/lib/udev</filename>; otherwise, the
|
|
absolute path must be specified.</para>
|
|
<para>This is the default if no <replaceable>type</replaceable>
|
|
is specified.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>builtin</literal></term>
|
|
<listitem>
|
|
<para>As <varname>program</varname>, but use one of the
|
|
built-in programs rather than an external one.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<para>The program name and following arguments are separated by spaces. Single quotes can be
|
|
used to specify arguments with spaces.</para>
|
|
|
|
<para>This can only be used for very short-running foreground tasks. Running an event process for
|
|
a long period of time may block all further events for this or a dependent device.</para>
|
|
|
|
<para>Note that running programs that access the network or mount/unmount filesystems is not
|
|
allowed inside of udev rules, due to the default sandbox that is enforced on
|
|
<filename>systemd-udevd.service</filename>.</para>
|
|
|
|
<para>Starting daemons or other long-running processes is not allowed; the forked processes,
|
|
detached or not, will be unconditionally killed after the event handling has finished. In order
|
|
to activate long-running processes from udev rules, provide a service unit and pull it in from a
|
|
udev device using the <varname>SYSTEMD_WANTS</varname> device property. See
|
|
<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
for details.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>LABEL</varname></term>
|
|
<listitem>
|
|
<para>A named label to which a <varname>GOTO</varname> may jump.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>GOTO</varname></term>
|
|
<listitem>
|
|
<para>Jumps to the next <varname>LABEL</varname> with a matching name.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>IMPORT{<replaceable>type</replaceable>}</varname></term>
|
|
<listitem>
|
|
<para>Import a set of variables as device properties, depending on
|
|
<replaceable>type</replaceable>:</para>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><literal>program</literal></term>
|
|
<listitem>
|
|
<para>Execute an external program specified as the assigned
|
|
value and, if it returns successfully,
|
|
import its output, which must be in environment key
|
|
format. Path specification, command/argument separation,
|
|
and quoting work like in <varname>RUN</varname>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>builtin</literal></term>
|
|
<listitem>
|
|
<para>Similar to <literal>program</literal>, but use one of the
|
|
built-in programs rather than an external one.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>file</literal></term>
|
|
<listitem>
|
|
<para>Import a text file specified as the assigned value, the content
|
|
of which must be in environment key format.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>db</literal></term>
|
|
<listitem>
|
|
<para>Import a single property specified as the assigned value from the
|
|
current device database. This works only if the database is already populated
|
|
by an earlier event.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>cmdline</literal></term>
|
|
<listitem>
|
|
<para>Import a single property from the kernel command line. For simple flags
|
|
the value of the property is set to <literal>1</literal>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>parent</literal></term>
|
|
<listitem>
|
|
<para>Import the stored keys from the parent device by reading
|
|
the database entry of the parent device. The value assigned to
|
|
<option>IMPORT{parent}</option> is used as a filter of key names
|
|
to import (with the same shell glob pattern matching used for
|
|
comparisons).</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<para>This can only be used for very short-running foreground tasks. For details see
|
|
<option>RUN</option>.</para>
|
|
|
|
<para>Note that multiple <varname>IMPORT{}</varname> keys may be specified in one rule, and
|
|
<literal>=</literal>, <literal>:=</literal>, and <literal>+=</literal> have the same effect as
|
|
<literal>==</literal>. The key is true if the import is successful, unless <literal>!=</literal>
|
|
is used as the operator which causes the key to be true if the import failed.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>OPTIONS</varname></term>
|
|
<listitem>
|
|
<para>Rule and device options:</para>
|
|
<variablelist class='udev-directives'>
|
|
<varlistentry>
|
|
<term><option>link_priority=<replaceable>value</replaceable></option></term>
|
|
<listitem>
|
|
<para>Specify the priority of the created symlinks. Devices with higher
|
|
priorities overwrite existing symlinks of other devices. The default is 0.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><option>string_escape=<replaceable>none|replace</replaceable></option></term>
|
|
<listitem>
|
|
<para>Usually, control and other possibly unsafe characters are replaced
|
|
in strings used for device naming. The mode of replacement can be specified
|
|
with this option.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><option>static_node=</option></term>
|
|
<listitem>
|
|
<para>Apply the permissions specified in this rule to the
|
|
static device node with the specified name. Also, for every
|
|
tag specified in this rule, create a symlink
|
|
in the directory
|
|
<filename>/run/udev/static_node-tags/<replaceable>tag</replaceable></filename>
|
|
pointing at the static device node with the specified name.
|
|
Static device node creation is performed by systemd-tmpfiles
|
|
before systemd-udevd is started. The static nodes might not
|
|
have a corresponding kernel device; they are used to trigger
|
|
automatic kernel module loading when they are accessed.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><option>watch</option></term>
|
|
<listitem>
|
|
<para>Watch the device node with inotify; when the node is
|
|
closed after being opened for writing, a change uevent is
|
|
synthesized.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><option>nowatch</option></term>
|
|
<listitem>
|
|
<para>Disable the watching of a device node with inotify.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><option>db_persist</option></term>
|
|
<listitem>
|
|
<para>Set the flag (sticky bit) on the udev database entry
|
|
of the event device. Device properties are then kept in the
|
|
database even when
|
|
<command>udevadm info --cleanup-db</command> is called.
|
|
This option can be useful in certain cases
|
|
(e.g. Device Mapper devices) for persisting device state
|
|
on the transition from initramfs.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><option>log_level=<replaceable>level</replaceable></option></term>
|
|
<listitem>
|
|
<para>Takes a log level name like <literal>debug</literal> or
|
|
<literal>info</literal>, or a special value <literal>reset</literal>. When a log
|
|
level name is specified, the maximum log level is changed to that level. When
|
|
<literal>reset</literal> is set, then the previously specified log level is
|
|
revoked. Defaults to the log level of the main process of
|
|
<command>systemd-udevd</command>.</para>
|
|
<para>This may be useful when debugging events for certain devices. Note that the
|
|
log level is applied when the line including this rule is processed. So, for
|
|
debugging, it is recommended that this is specified at earlier place, e.g., the
|
|
first line of <filename>00-debug.rules</filename>.</para>
|
|
<para>Example for debugging uevent processing for network interfaces.
|
|
<programlisting># /etc/udev/rules.d/00-debug-net.rules
|
|
SUBSYSTEM=="net", OPTIONS="log_level=debug"</programlisting></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<para>The <varname>NAME</varname>, <varname>SYMLINK</varname>,
|
|
<varname>PROGRAM</varname>, <varname>OWNER</varname>,
|
|
<varname>GROUP</varname>, <varname>MODE</varname>, <varname>SECLABEL</varname>,
|
|
and <varname>RUN</varname> fields support simple string substitutions.
|
|
The <varname>RUN</varname> substitutions are performed after all rules
|
|
have been processed, right before the program is executed, allowing for
|
|
the use of device properties set by earlier matching rules. For all other
|
|
fields, substitutions are performed while the individual rule is being
|
|
processed. The available substitutions are:</para>
|
|
<variablelist class='udev-directives'>
|
|
<varlistentry>
|
|
<term><option>$kernel</option>, <option>%k</option></term>
|
|
<listitem>
|
|
<para>The kernel name for this device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$number</option>, <option>%n</option></term>
|
|
<listitem>
|
|
<para>The kernel number for this device. For example, <literal>sda3</literal> has kernel number
|
|
3.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$devpath</option>, <option>%p</option></term>
|
|
<listitem>
|
|
<para>The devpath of the device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$id</option>, <option>%b</option></term>
|
|
<listitem>
|
|
<para>The name of the device matched while searching the devpath
|
|
upwards for <option>SUBSYSTEMS</option>, <option>KERNELS</option>,
|
|
<option>DRIVERS</option>, and <option>ATTRS</option>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$driver</option></term>
|
|
<listitem>
|
|
<para>The driver name of the device matched while searching the
|
|
devpath upwards for <option>SUBSYSTEMS</option>,
|
|
<option>KERNELS</option>, <option>DRIVERS</option>, and
|
|
<option>ATTRS</option>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$attr{<replaceable>file</replaceable>}</option>, <option>%s{<replaceable>file</replaceable>}</option></term>
|
|
<listitem>
|
|
<para>The value of a sysfs attribute found at the device where
|
|
all keys of the rule have matched. If the matching device does not
|
|
have such an attribute, and a previous <option>KERNELS</option>,
|
|
<option>SUBSYSTEMS</option>, <option>DRIVERS</option>, or
|
|
<option>ATTRS</option> test selected a parent device, then the
|
|
attribute from that parent device is used.
|
|
</para>
|
|
<para>If the attribute is a symlink, the last element of the
|
|
symlink target is returned as the value.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$env{<replaceable>key</replaceable>}</option>, <option>%E{<replaceable>key</replaceable>}</option></term>
|
|
<listitem>
|
|
<para>A device property value.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$major</option>, <option>%M</option></term>
|
|
<listitem>
|
|
<para>The kernel major number for the device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$minor</option>, <option>%m</option></term>
|
|
<listitem>
|
|
<para>The kernel minor number for the device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$result</option>, <option>%c</option></term>
|
|
<listitem>
|
|
<para>The string returned by the external program requested with
|
|
<varname>PROGRAM</varname>.
|
|
A single part of the string, separated by a space character, may be selected
|
|
by specifying the part number as an attribute: <literal>%c{N}</literal>.
|
|
If the number is followed by the <literal>+</literal> character, this part plus all remaining parts
|
|
of the result string are substituted: <literal>%c{N+}</literal>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$parent</option>, <option>%P</option></term>
|
|
<listitem>
|
|
<para>The node name of the parent device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$name</option></term>
|
|
<listitem>
|
|
<para>The current name of the device. If not changed by a rule, it is the
|
|
name of the kernel device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$links</option></term>
|
|
<listitem>
|
|
<para>A space-separated list of the current symlinks. The value is
|
|
only set during a remove event or if an earlier rule assigned a value.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$root</option>, <option>%r</option></term>
|
|
<listitem>
|
|
<para>The udev_root value.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$sys</option>, <option>%S</option></term>
|
|
<listitem>
|
|
<para>The sysfs mount point.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$devnode</option>, <option>%N</option></term>
|
|
<listitem>
|
|
<para>The name of the device node.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>%%</option></term>
|
|
<listitem>
|
|
<para>The <literal>%</literal> character itself.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$$</option></term>
|
|
<listitem>
|
|
<para>The <literal>$</literal> character itself.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</refsect2>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<para>
|
|
<citerefentry>
|
|
<refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
|
|
</citerefentry>,
|
|
<citerefentry>
|
|
<refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
|
|
</citerefentry>,
|
|
<citerefentry>
|
|
<refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum>
|
|
</citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
</refentry>
|