chiark / gitweb /
doc: balance C indirections in function prototypes
[elogind.git] / man / udev.xml
index 773635e..da4ff22 100644 (file)
@@ -30,7 +30,7 @@
 
   <refnamediv>
     <refname>udev</refname>
-    <refpurpose>Linux dynamic device management</refpurpose>
+    <refpurpose>Dynamic device management</refpurpose>
   </refnamediv>
 
   <refsect1><title>Description</title>
     sources is provided by the library libudev.</para>
   </refsect1>
 
-  <refsect1><title>Configuration</title>
-    <para>udev configuration files are placed in <filename>/etc/udev</filename>
-    and <filename>/usr/lib/udev</filename>. All empty lines or lines beginning with
-    '#' are ignored.</para>
-
-    <refsect2><title>Configuration file</title>
-      <para>udev expects its main configuration file at <filename>/etc/udev/udev.conf</filename>.
-      It consists of a set of variables allowing the user to override default udev values.
-      The following variables can be set:</para>
-      <variablelist>
-        <varlistentry>
-          <term><varname>udev_log</varname></term>
-          <listitem>
-            <para>The logging priority. Valid values are the numerical syslog priorities
-            or their textual representations: <option>err</option>, <option>info</option>
-            and <option>debug</option>.</para>
-          </listitem>
-        </varlistentry>
-      </variablelist>
-    </refsect2>
-
-    <refsect2><title>Rules files</title>
+  <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 file names replace each other. Files in <filename>/etc</filename>
+      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>/lib</filename>. This can be
+      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>/lib</filename>, pointing to <filename>/dev/null</filename>,
-      disables the rules file entirely.</para>
-
-      <para>Rule files must have the extension <filename>.rules</filename>; other
-      extensions are ignored.</para>
+      <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 are matching against its value, the rule gets applied and the
-      assignment keys get the specified value assigned.</para>
+      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
       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>
+      <variablelist class='udev-directives'>
         <varlistentry>
-          <term><option>ACTION</option></term>
+          <term><varname>ACTION</varname></term>
           <listitem>
             <para>Match the name of the event action.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>DEVPATH</option></term>
+          <term><varname>DEVPATH</varname></term>
           <listitem>
             <para>Match the devpath of the event device.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>KERNEL</option></term>
+          <term><varname>KERNEL</varname></term>
           <listitem>
             <para>Match the name of the event device.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>NAME</option></term>
+          <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>
         </varlistentry>
 
         <varlistentry>
-          <term><option>SYMLINK</option></term>
+          <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
         </varlistentry>
 
         <varlistentry>
-          <term><option>SUBSYSTEM</option></term>
+          <term><varname>SUBSYSTEM</varname></term>
           <listitem>
             <para>Match the subsystem of the event device.</para>
           </listitem>
         </varlistentry>
         <varlistentry>
-          <term><option>DRIVER</option></term>
+          <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><option>ATTR{<replaceable>filename</replaceable>}</option></term>
+          <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
         </varlistentry>
 
         <varlistentry>
-          <term><option>KERNELS</option></term>
+          <term><varname>KERNELS</varname></term>
           <listitem>
             <para>Search the devpath upwards for a matching device name.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>SUBSYSTEMS</option></term>
+          <term><varname>SUBSYSTEMS</varname></term>
           <listitem>
             <para>Search the devpath upwards for a matching device subsystem name.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>DRIVERS</option></term>
+          <term><varname>DRIVERS</varname></term>
           <listitem>
             <para>Search the devpath upwards for a matching device driver name.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>ATTRS{<replaceable>filename</replaceable>}</option></term>
+          <term><varname>ATTRS{<replaceable>filename</replaceable>}</varname></term>
           <listitem>
             <para>Search the devpath upwards for a device with matching sysfs attribute values.
-            If multiple <option>ATTRS</option> matches are specified, all of them
+            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><option>TAGS</option></term>
+          <term><varname>TAGS</varname></term>
           <listitem>
             <para>Search the devpath upwards for a device with matching tag.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>ENV{<replaceable>key</replaceable>}</option></term>
+          <term><varname>ENV{<replaceable>key</replaceable>}</varname></term>
           <listitem>
             <para>Match against a device property value.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>TAG</option></term>
+          <term><varname>TAG</varname></term>
           <listitem>
             <para>Match against a device tag.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>TEST{<replaceable>octal mode mask</replaceable>}</option></term>
+          <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>
         </varlistentry>
 
         <varlistentry>
-          <term><option>PROGRAM</option></term>
+          <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 stdout
-            is available in the RESULT key.</para>
-            <para>This can only be used for very short-running foreground tasks. For details
-            see <option>RUN</option>.</para>
+            executed program in the environment. The program's standard ouput
+            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><option>RESULT</option></term>
+          <term><varname>RESULT</varname></term>
           <listitem>
-            <para>Match the returned string of the last PROGRAM call. This key can
-            be used in the same or in any later rule after a PROGRAM call.</para>
+            <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-style pattern matching. The following
+      <para>Most of the fields support shell glob pattern matching. The following
       pattern characters are supported:</para>
       <variablelist>
         <varlistentry>
           <term><literal>[]</literal></term>
           <listitem>
             <para>Matches any single character specified within the brackets. For
-            example, the pattern string 'tty[SR]' would match either 'ttyS' or 'ttyR'.
-            Ranges are also supported via the '-' character.
-            For example, to match on the range of all digits, the pattern [0-9] could
-            be used. If the first character following the '[' is a '!', any characters
-            not enclosed are matched.</para>
+            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>
       </variablelist>
 
       <para>The following keys can get values assigned:</para>
-      <variablelist>
+      <variablelist class='udev-directives'>
         <varlistentry>
-          <term><option>NAME</option></term>
+          <term><varname>NAME</varname></term>
           <listitem>
             <para>The name to use for a network interface. The name of a device node
             cannot be changed by udev, only additional symlinks can be created.</para>
         </varlistentry>
 
         <varlistentry>
-          <term><option>SYMLINK</option></term>
+          <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 [0-9A-Za-z#+-.:=@_/], valid utf8 character sequences,
-            and "\x00" hex encoding. All other characters are replaced by
-            a '_' character.</para>
+            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
         </varlistentry>
 
         <varlistentry>
-          <term><option>OWNER</option>, <option>GROUP</option>, <option>MODE</option></term>
+          <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>
         </varlistentry>
 
         <varlistentry>
-          <term><option>ATTR{<replaceable>key</replaceable>}</option></term>
+          <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>
         </varlistentry>
 
         <varlistentry>
-          <term><option>ENV{<replaceable>key</replaceable>}</option></term>
+          <term><varname>ENV{<replaceable>key</replaceable>}</varname></term>
           <listitem>
-            <para>Set a device property value. Property names with a leading '.'
+            <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, say, the PROGRAM match key).</para>
+            external tools (run by, for example, the <varname>PROGRAM</varname>
+            match key).</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>TAG</option></term>
+          <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
         </varlistentry>
 
         <varlistentry>
-          <term><option>RUN</option></term>
+          <term><varname>RUN{<replaceable>type</replaceable>}</varname></term>
           <listitem>
-            <para>Add a program to the list of programs to be executed for a specific
-            device.</para>
-            <para>If no absolute path is given, the program is expected to live in
-            /usr/lib/udev, otherwise the absolute path must be specified. The program
-            name and following arguments are separated by spaces. Single quotes can
-            be used to specify arguments with spaces.</para>
+            <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
+            <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><option>LABEL</option></term>
+          <term><varname>LABEL</varname></term>
           <listitem>
-            <para>A named label to which a GOTO may jump.</para>
+            <para>A named label to which a <varname>GOTO</varname> may jump.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>GOTO</option></term>
+          <term><varname>GOTO</varname></term>
           <listitem>
-            <para>Jumps to the next LABEL with a matching name.</para>
+            <para>Jumps to the next <varname>LABEL</varname> with a matching name.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><option>IMPORT{<replaceable>type</replaceable>}</option></term>
+          <term><varname>IMPORT{<replaceable>type</replaceable>}</varname></term>
           <listitem>
             <para>Import a set of variables as device properties,
             depending on <literal>type</literal>:</para>
                   <para>Execute an external program specified as the assigned value and
                   import its output, which must be in environment key
                   format. Path specification, command/argument separation,
-                  and quoting work like in <option>RUN</option>.</para>
+                  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
                 <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 '1'.</para>
+                  the value of the property is set to <literal>1</literal>.</para>
                 </listitem>
               </varlistentry>
               <varlistentry>
                   <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-style pattern matching used for
+                  to import (with the same shell glob pattern matching used for
                   comparisons).</para>
                 </listitem>
               </varlistentry>
         </varlistentry>
 
         <varlistentry>
-          <term><option>WAIT_FOR</option></term>
+          <term><varname>WAIT_FOR</varname></term>
           <listitem>
             <para>Wait for a file to become available or until a timeout of
             10 seconds expires. The path is relative to the sysfs device;
         </varlistentry>
 
         <varlistentry>
-          <term><option>OPTIONS</option></term>
+          <term><varname>OPTIONS</varname></term>
           <listitem>
             <para>Rule and device options:</para>
-            <variablelist>
+            <variablelist class='udev-directives'>
               <varlistentry>
                 <term><option>link_priority=<replaceable>value</replaceable></option></term>
                 <listitem>
               <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. Static device node creation can be requested by kernel modules.
-                  These nodes might not have a corresponding kernel device at the time systemd-udevd is
-                  started; they can trigger automatic kernel module loading.</para>
+                  <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>
+                  <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>
         </varlistentry>
       </variablelist>
 
-      <para>The <option>NAME</option>, <option>SYMLINK</option>, <option>PROGRAM</option>,
-      <option>OWNER</option>, <option>GROUP</option>, <option>MODE</option>  and  <option>RUN</option>
-      fields support simple string substitutions. The <option>RUN</option>
-      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>
+      <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>$kernel</option>, <option>%k</option></term>
           <listitem>
         <varlistentry>
           <term><option>$number</option>, <option>%n</option></term>
           <listitem>
-            <para>The kernel number for this device. For example, 'sda3' has
-            kernel number of '3'</para>
+            <para>The kernel number for this device. For example,
+              <literal>sda3</literal> has kernel number <literal>3</literal>.
+            </para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
           <term><option>$id</option>, <option>%b</option></term>
           <listitem>
-            <para>The name of the device matched while searching the devpath upwards for
-              <option>SUBSYSTEMS</option>, <option>KERNELS</option>, <option>DRIVERS</option> and <option>ATTRS</option>.
+            <para>The name of the device matched while searching the devpath
+              upwards for <option>SUBSYSTEMS</option>, <option>KERNELS</option>,
+              <option>DRIVERS</option>, and <option>ATTRS</option>.
             </para>
           </listitem>
         </varlistentry>
         <varlistentry>
           <term><option>$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>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>
           <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 KERNELS, SUBSYSTEMS, DRIVERS, or
-            ATTRS 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>
+              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>$result</option>, <option>%c</option></term>
           <listitem>
-            <para>The string returned by the external program requested with PROGRAM.
+            <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: <option>%c{N}</option>.
-            If the number is followed by the '+' character, this part plus all remaining parts
-            of the result string are substituted: <option>%c{N+}</option></para>
+            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>
 
         <varlistentry>
-          <term><literal>%%</literal></term>
+          <term><option>%%</option></term>
           <listitem>
-          <para>The '%' character itself.</para>
+          <para>The <literal>%</literal> character itself.</para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><literal>$$</literal></term>
+          <term><option>$$</option></term>
           <listitem>
-          <para>The '$' character itself.</para>
+          <para>The <literal>$</literal> character itself.</para>
+          </listitem>
+        </varlistentry>
+      </variablelist>
+  </refsect1>
+
+  <refsect1><title>Hardware Database Files</title>
+      <para>The hwdb files are read from the files located in the
+      system hwdb directory <filename>/usr/lib/udev/hwdb.d</filename>,
+      the volatile runtime directory <filename>/run/udev/hwdb.d</filename>
+      and the local administration directory <filename>/etc/udev/hwdb.d</filename>.
+      All hwdb 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 hwdb file with a local file if needed;
+      a symlink in <filename>/etc</filename> with the same name as a hwdb file in
+      <filename>/usr/lib</filename>, pointing to <filename>/dev/null</filename>,
+      disables the hwdb file entirely. hwdb files must have the extension
+      <filename>.hwdb</filename>; other extensions are ignored.</para>
+
+      <para>The hwdb file contains data records consisting of matches and
+      associated key-value pairs. Every record in the hwdb starts with one or
+      more match string, specifying a shell glob to compare the database
+      lookup string against. Multiple match lines are specified in additional
+      consecutive lines. Every match line is compared indivdually, they are
+      combined by OR. Every match line must start at the first character of
+      the line.</para>
+
+      <para>The match lines are followed by one or more key-value pair lines, which
+      are recognized by a leading space character. The key name and value are separated
+      by <literal>=</literal>. An empty line signifies the end
+      of a record. Lines beginning with <literal>#</literal> are ignored.</para>
+
+      <para>The content of all hwdb files is read by
+      <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+      and compiled to a binary database located at <filename>/etc/udev/hwdb.bin</filename>.
+      During runtime only the binary database is used.</para>
+  </refsect1>
+
+  <refsect1><title>Network Link Configuration</title>
+      <para>Network link configuration is performed by the <literal>net_setup_link</literal>
+      udev builtin.</para>
+
+      <para>The link files are read from the files located in the
+      system network directory <filename>/usr/lib/systemd/network</filename>,
+      the volatile runtime network directory <filename>/run/systemd/network</filename>
+      and the local administration network directory <filename>/etc/systemd/network</filename>.
+      Link files must have the extension <filename>.link</filename>; other extensions are ignored.
+      All link 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 link file with a local file if needed;
+      a symlink in <filename>/etc</filename> with the same name as a link file in
+      <filename>/usr/lib</filename>, pointing to <filename>/dev/null</filename>,
+      disables the link file entirely.</para>
+
+      <para>The link file contains a <literal>[Match]</literal> section, which
+      determines if a given link file may be applied to a given device; and a
+      <literal>[Link]</literal> section specifying how the device should be
+      configured. The first (in lexical order) of the link files that matches
+      a given device is applied.</para>
+
+      <para>A link file is said to match a device if each of the entries in the
+      <literal>[Match]</literal> section matches, or if the section is empty.
+      The following keys are accepted:</para>
+
+      <variablelist class='network-directives'>
+        <varlistentry>
+          <term><varname>MACAddress</varname></term>
+          <listitem>
+            <para>The hardware address.
+            </para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>Path</varname></term>
+          <listitem>
+            <para>The persistent path, as exposed by the udev property <literal>ID_PATH</literal>.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>Driver</varname></term>
+          <listitem>
+            <para>The driver currently bound to the device, as exposed by the udev property <literal>DRIVER</literal>.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>Type</varname></term>
+          <listitem>
+            <para>The device type, as exposed by the udev property <literal>DEVTYPE</literal>.</para>
+          </listitem>
+        </varlistentry>
+      </variablelist>
+
+      <para>The <literal>[Link]</literal> section accepts the following keys:</para>
+
+      <variablelist class='network-directives'>
+        <varlistentry>
+          <term><varname>Description</varname></term>
+          <listitem>
+            <para>A description of the device.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>Alias</varname></term>
+          <listitem>
+            <para>The <literal>ifalias</literal> is set to this value.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>MACAddressPolicy</varname></term>
+          <listitem>
+            <para>The policy by which the MAC address should be set. The
+              available policies are:
+            </para>
+            <variablelist>
+              <varlistentry>
+                <term><literal>persistent</literal></term>
+                <listitem>
+                  <para>If the hardware has a persistent MAC address, as most
+                    hardware should, and this is used by the kernel, nothing is
+                    done. Otherwise, a new MAC address is generated which is
+                    guaranteed to be the same on every boot for the given
+                    machine and the given device, but which is otherwise random.
+                  </para>
+                </listitem>
+              </varlistentry>
+              <varlistentry>
+                <term><literal>random</literal></term>
+                <listitem>
+                  <para>If the kernel is using a random MAC address, nothing is
+                    done. Otherwise, a new address is randomly generated each
+                    time the device appears, typically at boot.
+                  </para>
+                </listitem>
+              </varlistentry>
+            </variablelist>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>MACAddress</varname></term>
+          <listitem>
+            <para>The MAC address to use, if no <literal>MACAddressPolicy</literal>
+              is specified.
+            </para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>NamePolicy</varname></term>
+          <listitem>
+            <para>An ordered, space-separated list of policies by which the
+              interface name should be set. <literal>NamePolicy</literal> may
+              be disabeled by specifying <literal>net.ifnames=0</literal> on the
+              kernel commandline. Each of the policies may fail, and the first
+              successfull one is used. The name is not set directly, but
+              is exported to udev as the property <literal>ID_NET_NAME</literal>,
+              which is, by default, used by a udev rule to set
+              <literal>NAME</literal>. The available policies are:
+            </para>
+            <variablelist>
+              <varlistentry>
+                <term><literal>onboard</literal></term>
+                <listitem>
+                  <para>The name is set based on information given by the
+                    firmware for on-board devices, as exported by the udev
+                    property <literal>ID_NET_NAME_ONBOARD</literal>.
+                  </para>
+                </listitem>
+              </varlistentry>
+              <varlistentry>
+                <term><literal>slot</literal></term>
+                <listitem>
+                  <para>The name is set based on information given by the
+                    firmware for hot-plug devices, as exported by the udev
+                    property <literal>ID_NET_NAME_SLOT</literal>.
+                  </para>
+                </listitem>
+              </varlistentry>
+              <varlistentry>
+                <term><literal>path</literal></term>
+                <listitem>
+                  <para>The name is set based on the device's physical location,
+                    as exported by the udev property
+                    <literal>ID_NET_NAME_PATH</literal>.
+                  </para>
+                </listitem>
+              </varlistentry>
+              <varlistentry>
+                <term><literal>mac</literal></term>
+                <listitem>
+                  <para>The name is set based on the device's persistent MAC
+                    address, as exported by the udev property
+                    <literal>ID_NET_NAME_MAC</literal>.
+                  </para>
+                </listitem>
+              </varlistentry>
+            </variablelist>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>Name</varname></term>
+          <listitem>
+            <para>The interface name to use in case all the policies specified
+              in <literal>NamePolicy</literal> fail, or in case
+              <literal>NamePolicy</literal> is missing or disabled.
+            </para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>MTU</varname></term>
+          <listitem>
+            <para>The MTU to set for the device.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>SpeedMBytes</varname></term>
+          <listitem>
+            <para>The speed to set for the device.</para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>Duplex</varname></term>
+          <listitem>
+            <para>The duplex mode to set for the device. The accepted values
+              are <literal>half</literal> and <literal>full</literal>.
+            </para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><varname>WakeOnLan</varname></term>
+          <listitem>
+            <para>The Wake-on-LAN policy to set for the device. The supported
+              values are:
+            </para>
+            <variablelist>
+              <varlistentry>
+                <term><literal>phy</literal></term>
+                <listitem>
+                  <para>Wake on PHY activity.</para>
+                </listitem>
+              </varlistentry>
+              <varlistentry>
+                <term><literal>magic</literal></term>
+                <listitem>
+                  <para>Wake on receipt of a magic packet.</para>
+                </listitem>
+              </varlistentry>
+              <varlistentry>
+                <term><literal>off</literal></term>
+                <listitem>
+                  <para>Never wake.</para>
+                </listitem>
+              </varlistentry>
+            </variablelist>
           </listitem>
         </varlistentry>
       </variablelist>
-    </refsect2>
   </refsect1>
 
   <refsect1>
     <title>See Also</title>
-    <para><citerefentry>
+    <para>
+      <citerefentry>
         <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum>
       </citerefentry>,
       <citerefentry>
         <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
-    </citerefentry></para>
+      </citerefentry>
+    </para>
   </refsect1>
 </refentry>