Adding upstream version 252.22.upstream/252.22upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 860 insertions, 0 deletions

diff --git a/man/udev.xml b/man/udev.xml
new file mode 100644
index 0000000..332c7ac
--- /dev/null
+++ b/man/udev.xml
@@ -0,0 +1,860 @@
+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+  SPDX-License-Identifier: LGPL-2.1-or-later
+  Copyright © 2014 Jason St. John
+-->
+
+<refentry id="udev">
+  <refentryinfo>
+    <title>udev</title>
+    <productname>systemd</productname>
+  </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 directories
+      <filename>/usr/lib/udev/rules.d</filename> and <filename>/usr/local/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 under
+      <filename>/usr/</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-operator-value expressions.
+      Each expression has a distinct effect, depending on the key and operator used.</para>
+
+      <refsect2>
+        <title>Operators</title>
+        <variablelist>
+          <varlistentry>
+            <term><literal>==</literal></term>
+            <listitem>
+              <para>Compare for equality. (The specified key has the specified value.)</para>
+            </listitem>
+          </varlistentry>
+
+          <varlistentry>
+            <term><literal>!=</literal></term>
+            <listitem>
+              <para>Compare for inequality. (The specified key doesn't have the specified value, or the
+              specified key is not present at all.)
+              </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>
+      </refsect2>
+
+      <refsect2>
+        <title>Values</title>
+          <para>Values are written as double quoted strings, such as ("string").
+          To include a quotation mark (") in the value, precede it by a backslash (\").
+          Any other occurrences of a backslash followed by a character are not unescaped.
+          That is, "\t\n" is treated as four characters:
+          backslash, lowercase t, backslash, lowercase n.</para>
+
+          <para>The string can be prefixed with a lowercase e (e"string\n") to mark the string as
+          <ulink url="https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences">C-style escaped</ulink>.
+          For example, e"string\n" is parsed as 7 characters: 6 lowercase letters and a newline.
+          This can be useful for writing special characters when a kernel driver requires them.</para>
+
+          <para>Please note that <constant>NUL</constant> is not allowed in either string variant.</para>
+      </refsect2>
+
+      <refsect2>
+        <title>Keys</title>
+        <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>KERNELS</varname></term>
+            <listitem>
+              <para>Search the devpath upwards for a matching device name.</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. If the operator is <literal>!=</literal>, the token returns true only if there is no
+              symlink matched.</para>
+            </listitem>
+          </varlistentry>
+
+          <varlistentry>
+            <term><varname>SUBSYSTEM</varname></term>
+            <listitem>
+              <para>Match the subsystem of the event device.</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>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>DRIVERS</varname></term>
+            <listitem>
+              <para>Search the devpath upwards for a matching device driver name.</para>
+            </listitem>
+          </varlistentry>
+
+          <varlistentry>
+            <term><varname>ATTR{<replaceable>filename</replaceable>}</varname></term>
+            <listitem>
+              <para>Match sysfs attribute value of the event device.</para>
+
+              <para>Trailing whitespace in the attribute values is ignored unless the specified match value
+              itself contains trailing whitespace.</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.</para>
+
+              <para>Trailing whitespace in the attribute values is ignored unless the specified match value
+              itself contains trailing whitespace.</para>
+            </listitem>
+          </varlistentry>
+
+          <varlistentry>
+            <term><varname>SYSCTL{<replaceable>kernel parameter</replaceable>}</varname></term>
+            <listitem>
+              <para>Match a kernel parameter value.</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>CONST{<replaceable>key</replaceable>}</varname></term>
+            <listitem>
+              <para>Match against a system-wide constant. Supported keys are:</para>
+              <variablelist>
+                <varlistentry>
+                  <term><literal>arch</literal></term>
+                  <listitem>
+                    <para>System's architecture. See <option>ConditionArchitecture=</option> in
+                    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+                    for possible values.</para>
+                  </listitem>
+                </varlistentry>
+                <varlistentry>
+                  <term><literal>virt</literal></term>
+                  <listitem>
+                    <para>System's virtualization environment. See
+                    <citerefentry><refentrytitle>systemd-detect-virt</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+                    for possible values.</para>
+                  </listitem>
+                </varlistentry>
+              </variablelist>
+              <para>Unknown keys will never match.</para>
+            </listitem>
+          </varlistentry>
+
+          <varlistentry>
+            <term><varname>TAG</varname></term>
+            <listitem>
+              <para>Match against one of device tags. It can be used once a TAG key has been set in one of
+              the preceding rules. There may be multiple tags; only one needs to match. If the operator is
+              <literal>!=</literal>, the token returns true only if there is no tag matched.</para>
+            </listitem>
+          </varlistentry>
+
+          <varlistentry>
+            <term><varname>TAGS</varname></term>
+            <listitem>
+              <para>Search the devpath upwards for a device with matching tag. If the operator is
+              <literal>!=</literal>, the token returns true only if there is no tag matched.</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>
+
+              <para>Note that multiple <varname>PROGRAM</varname> keys may be specified in one rule, and
+              <literal>=</literal>, <literal>:=</literal>, and <literal>+=</literal> have the same effect as
+              <literal>==</literal>.</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>Specify a program to be executed after processing of all the rules for the event. With
+              <literal>+=</literal>, this invocation is added to the list, and with <literal>=</literal> or
+              <literal>:=</literal>, it replaces any previous contents of the list. Please note that both
+              <literal>program</literal> and <literal>builtin</literal> types described below share a common
+              list, so clearing the list with <literal>:=</literal> and <literal>=</literal> affects both
+              types.</para>
+
+              <para><replaceable>type</replaceable> may be:</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>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>When <literal>replace</literal>, possibly unsafe characters in strings
+                    assigned to <varname>NAME</varname>, <varname>SYMLINK</varname>, and
+                    <varname>ENV{<replaceable>key</replaceable>}</varname> are replaced. When
+                    <literal>none</literal>, no replacement is performed. When unset, the replacement
+                    is performed for <varname>NAME</varname>, <varname>SYMLINK</varname>, but not for
+                    <varname>ENV{<replaceable>key</replaceable>}</varname>. Defaults to unset.</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
+                    initrd.</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>