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+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<refentry id="udev">
+  <refentryinfo>
+    <title>udev</title>
+    <productname>systemd</productname>
+    <authorgroup>
+      <author>
+        <contrib>Developer</contrib>
+        <firstname>Greg</firstname>
+        <surname>Kroah-Hartmann</surname>
+        <email>greg@kroah.com</email>
+      </author>
+      <author>
+        <contrib>Developer</contrib>
+        <firstname>Kay</firstname>
+        <surname>Sievers</surname>
+        <email>kay@vrfy.org</email>
+      </author>
+    </authorgroup>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>udev</refentrytitle>
+    <manvolnum>7</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>udev</refname>
+    <refpurpose>Dynamic device management</refpurpose>
+  </refnamediv>
+
+  <refsect1><title>Description</title>
+    <para>udev supplies the system software with device events, manages permissions
+    of device nodes and may create additional symlinks in the <filename>/dev</filename>
+    directory, or renames network interfaces. The kernel usually just assigns unpredictable
+    device names based on the order of discovery. Meaningful symlinks or network device
+    names provide a way to reliably identify devices based on their properties or
+    current configuration.</para>
+
+    <para>The udev daemon, <citerefentry><refentrytitle>systemd-udevd.service</refentrytitle>
+    <manvolnum>8</manvolnum></citerefentry>, receives device uevents directly from
+    the kernel whenever a device is added or removed from the system, or it changes its
+    state. When udev receives a device event, it matches its configured set of rules
+    against various device attributes to identify the device. Rules that match may
+    provide additional device information to be stored in the udev database or
+    to be used to create meaningful symlink names.</para>
+
+    <para>All device information udev processes is stored in the udev database and
+    sent out to possible event subscribers. Access to all stored data and the event
+    sources is provided by the library libudev.</para>
+  </refsect1>
+
+  <refsect1><title>Rules Files</title>
+      <para>The udev rules are read from the files located in the
+      system rules directory <filename>/usr/lib/udev/rules.d</filename>,
+      the volatile runtime directory <filename>/run/udev/rules.d</filename>
+      and the local administration directory <filename>/etc/udev/rules.d</filename>.
+      All rules files are collectively sorted and processed in lexical order,
+      regardless of the directories in which they live. However, files with
+      identical filenames replace each other. Files in <filename>/etc</filename>
+      have the highest priority, files in <filename>/run</filename> take precedence
+      over files with the same name in <filename>/usr/lib</filename>. This can be
+      used to override a system-supplied rules file with a local file if needed;
+      a symlink in <filename>/etc</filename> with the same name as a rules file in
+      <filename>/usr/lib</filename>, pointing to <filename>/dev/null</filename>,
+      disables the rules file entirely. Rule files must have the extension
+      <filename>.rules</filename>; other extensions are ignored.</para>
+
+      <para>Every line in the rules file contains at least one key-value pair.
+      Except for empty lines or lines beginning with <literal>#</literal>, which are ignored.
+      There are two kinds of keys: match and assignment.
+      If all match keys match against their values, the rule gets applied and the
+      assignment keys get the specified values assigned.</para>
+
+      <para>A matching rule may rename a network interface, add symlinks
+      pointing to the device node, or run a specified program as part of
+      the event handling.</para>
+
+      <para>A rule consists of a comma-separated list of one or more key-value pairs.
+      Each key has a distinct operation, depending on the used operator. Valid
+      operators are:</para>
+      <variablelist>
+        <varlistentry>
+          <term><literal>==</literal></term>
+          <listitem>
+            <para>Compare for equality.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><literal>!=</literal></term>
+          <listitem>
+            <para>Compare for inequality.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><literal>=</literal></term>
+          <listitem>
+            <para>Assign a value to a key. Keys that represent a list are reset
+            and only this single value is assigned.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><literal>+=</literal></term>
+          <listitem>
+            <para>Add the value to a key that holds a list of entries.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><literal>-=</literal></term>
+          <listitem>
+            <para>Remove the value from a key that holds a list of entries.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><literal>:=</literal></term>
+          <listitem>
+            <para>Assign  a  value  to  a key finally; disallow any later changes.</para>
+          </listitem>
+        </varlistentry>
+      </variablelist>
+
+      <para>The following key names can be used to match against device properties.
+      Some of the keys also match against properties of the parent devices in sysfs,
+      not only the device that has generated the event. If multiple keys that match
+      a parent device are specified in a single rule, all these keys must match at
+      one and the same parent device.</para>
+      <variablelist class='udev-directives'>
+        <varlistentry>
+          <term><varname>ACTION</varname></term>
+          <listitem>
+            <para>Match the name of the event action.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>DEVPATH</varname></term>
+          <listitem>
+            <para>Match the devpath of the event device.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>KERNEL</varname></term>
+          <listitem>
+            <para>Match the name of the event device.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>NAME</varname></term>
+          <listitem>
+            <para>Match the name of a network interface. It can be used once the
+            NAME key has been set in one of the preceding rules.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>SYMLINK</varname></term>
+          <listitem>
+            <para>Match the name of a symlink targeting the node. It can
+            be used once a SYMLINK key has been set in one of the preceding
+            rules. There may be multiple symlinks; only one needs to match.
+            </para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>SUBSYSTEM</varname></term>
+          <listitem>
+            <para>Match the subsystem of the event device.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>DRIVER</varname></term>
+          <listitem>
+            <para>Match the driver name of the event device. Only set this key for devices
+            which are bound to a driver at the time the event is generated.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>ATTR{<replaceable>filename</replaceable>}</varname></term>
+          <listitem>
+            <para>Match sysfs attribute values of the event device. Trailing
+            whitespace in the attribute values is ignored unless the specified match
+            value itself contains trailing whitespace.
+            </para>
+          </listitem>
+          <term><varname>SYSCTL{<replaceable>kernel parameter</replaceable>}</varname></term>
+          <listitem>
+            <para>Match a kernel parameter value.
+            </para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>KERNELS</varname></term>
+          <listitem>
+            <para>Search the devpath upwards for a matching device name.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>SUBSYSTEMS</varname></term>
+          <listitem>
+            <para>Search the devpath upwards for a matching device subsystem name.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>DRIVERS</varname></term>
+          <listitem>
+            <para>Search the devpath upwards for a matching device driver name.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>ATTRS{<replaceable>filename</replaceable>}</varname></term>
+          <listitem>
+            <para>Search the devpath upwards for a device with matching sysfs attribute values.
+            If multiple <varname>ATTRS</varname> matches are specified, all of them
+            must match on the same device. Trailing whitespace in the attribute values is ignored
+            unless the specified match value itself contains trailing whitespace.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>TAGS</varname></term>
+          <listitem>
+            <para>Search the devpath upwards for a device with matching tag.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>ENV{<replaceable>key</replaceable>}</varname></term>
+          <listitem>
+            <para>Match against a device property value.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>TAG</varname></term>
+          <listitem>
+            <para>Match against a device tag.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>TEST{<replaceable>octal mode mask</replaceable>}</varname></term>
+          <listitem>
+            <para>Test the existence of a file. An octal mode mask can be specified
+            if needed.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>PROGRAM</varname></term>
+          <listitem>
+            <para>Execute a program to determine whether there
+            is a match; the key is true if the program returns
+            successfully. The device properties are made available to the
+            executed program in the environment. The program's standard output
+            is available in the <varname>RESULT</varname> key.</para>
+            <para>This can only be used for very short-running foreground tasks. For details,
+            see <varname>RUN</varname>.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>RESULT</varname></term>
+          <listitem>
+            <para>Match the returned string of the last <varname>PROGRAM</varname> call.
+            This key can be used in the same or in any later rule after a
+            <varname>PROGRAM</varname> call.</para>
+          </listitem>
+        </varlistentry>
+      </variablelist>
+
+      <para>Most of the fields support shell glob pattern matching and
+      alternate patterns. The following special characters are supported:</para>
+      <variablelist>
+        <varlistentry>
+          <term><literal>*</literal></term>
+          <listitem>
+            <para>Matches zero or more characters.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><literal>?</literal></term>
+          <listitem>
+            <para>Matches any single character.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><literal>[]</literal></term>
+          <listitem>
+            <para>Matches any single character specified within the brackets. For
+            example, the pattern string <literal>tty[SR]</literal>
+            would match either <literal>ttyS</literal> or <literal>ttyR</literal>.
+            Ranges are also supported via the <literal>-</literal> character.
+            For example, to match on the range of all digits, the pattern
+            <literal>[0-9]</literal> could be used. If the first character
+            following the <literal>[</literal> is a <literal>!</literal>,
+            any characters not enclosed are matched.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><literal>|</literal></term>
+          <listitem>
+            <para>Separates alternative patterns. For example, the pattern string
+            <literal>abc|x*</literal> would match either <literal>abc</literal>
+            or <literal>x*</literal>.</para>
+          </listitem>
+        </varlistentry>
+      </variablelist>
+
+      <para>The following keys can get values assigned:</para>
+      <variablelist class='udev-directives'>
+        <varlistentry>
+          <term><varname>NAME</varname></term>
+          <listitem>
+            <para>The name to use for a network interface. See
+            <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+            for a higher-level mechanism for setting the interface name.
+            The name of a device node cannot be changed by udev, only additional
+            symlinks can be created.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>SYMLINK</varname></term>
+          <listitem>
+            <para>The name of a symlink targeting the node. Every matching rule adds
+            this value to the list of symlinks to be created.</para>
+            <para>The set of characters to name a symlink is limited. Allowed
+            characters are <literal>0-9A-Za-z#+-.:=@_/</literal>, valid UTF-8 character
+            sequences, and <literal>\x00</literal> hex encoding. All other
+            characters are replaced by a <literal>_</literal> character.</para>
+            <para>Multiple symlinks may be specified by separating the names by the
+            space character. In case multiple devices claim the same name, the link
+            always points to the device with the highest link_priority. If the current
+            device goes away, the links are re-evaluated and the device with the
+            next highest link_priority becomes the owner of the link. If no
+            link_priority is specified, the order of the devices (and which one of
+            them owns the link) is undefined.</para>
+            <para>Symlink names must never conflict with the kernel's default device
+            node names, as that would result in unpredictable behavior.
+            </para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>OWNER</varname>, <varname>GROUP</varname>, <varname>MODE</varname></term>
+          <listitem>
+            <para>The permissions for the device node. Every specified value overrides
+            the compiled-in default value.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>SECLABEL{<replaceable>module</replaceable>}</varname></term>
+          <listitem>
+            <para>Applies the specified Linux Security Module label to the device node.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>ATTR{<replaceable>key</replaceable>}</varname></term>
+          <listitem>
+            <para>The value that should be written to a sysfs attribute of the
+            event device.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>SYSCTL{<replaceable>kernel parameter</replaceable>}</varname></term>
+          <listitem>
+            <para>The value that should be written to kernel parameter.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>ENV{<replaceable>key</replaceable>}</varname></term>
+          <listitem>
+            <para>Set a device property value. Property names with a leading <literal>.</literal>
+            are neither stored in the database nor exported to events or
+            external tools (run by, for example, the <varname>PROGRAM</varname>
+            match key).</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>TAG</varname></term>
+          <listitem>
+            <para>Attach a tag to a device. This is used to filter events for users
+            of libudev's monitor functionality, or to enumerate a group of tagged
+            devices. The implementation can only work efficiently if only a few
+            tags are attached to a device. It is only meant to be used in
+            contexts with specific device filter requirements, and not as a
+            general-purpose flag. Excessive use might result in inefficient event
+            handling.</para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><varname>RUN{<replaceable>type</replaceable>}</varname></term>
+          <listitem>
+            <para>Add a program to the list of programs to be executed after
+            processing all the rules for a specific event, depending on
+            <literal>type</literal>:</para>
+            <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>Starting daemons or other long-running processes is not appropriate
+            for udev; the forked processes, detached or not, will be unconditionally
+            killed after the event handling has finished.</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 <literal>type</literal>:</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>
+          </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>
+            </variablelist>
+          </listitem>
+        </varlistentry>
+      </variablelist>
+
+      <para>The <varname>NAME</varname>, <varname>SYMLINK</varname>,
+      <varname>PROGRAM</varname>, <varname>OWNER</varname>,
+      <varname>GROUP</varname>, <varname>MODE</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 <literal>3</literal>.
+            </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>
+  </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>