path: root/docs/udev.xml

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<article>
  <articleinfo>
    <title>xmlto</title>
    <author>
      <firstname>Kay</firstname>
      <surname>Sievers</surname>
      <email>kay.sievers@vrfy.org</email>
    </author>
    <copyright>
      <year>2005</year>
      <holder>Kay Sievers</holder>
    </copyright>
  </articleinfo>

  <section>
    <title>udev</title>
    <refentry>
      <refentryinfo>
        <title>udev</title>
        <date>August 2005</date>
        <productname>udev</productname>
      </refentryinfo>

      <refmeta>
        <refentrytitle>udev</refentrytitle>
        <manvolnum>8</manvolnum>
      </refmeta>

      <refnamediv>
        <refname>udev</refname>
        <refpurpose>dynamic device management</refpurpose>
      </refnamediv>

      <refsect1><title>DESCRIPTION</title>
        <para>udev provides a dynamic device directory containing only the files for
        actually present devices. It creates or removes device node files in the
        <filename>/dev</filename> directory, or it renames network interfaces.</para>

        <para>Usually udev runs as <citerefentry><refentrytitle>udevd</refentrytitle>
        <manvolnum>8</manvolnum></citerefentry> and receives uevents directly from the
        kernel if a device is added or removed form the system. The program
        <command>udev</command> itself may be used as an event handler in situations,
        where running the daemon is not appropriate, like in initramfs.</para>

        <para>If udev receives a device event, it matches its configured rules
        against the available device attributes provided in sysfs to identify the device.
        Rules that match, may provide additional device information or specify a device
        node name and multiple symlink names and instruct udev to run additional programs
        as part of the device event handling.</para>
      </refsect1>

      <refsect1><title>CONFIGURATION</title>
        <para>All udev configuration files are placed in <filename>/etc/udev/*</filename>.
        Every file consist of a set of lines of text. All empty lines or lines beginning
        with '#' will be 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><option>udev_root</option></term>
              <listitem>
                <para>Specifies where to place the device nodes in the filesystem.
                The default value is <filename>/dev</filename>.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>udev_db</option></term>
              <listitem>
                <para>The name and location of the udev database. The default value is
                <filename>/dev/.udevdb</filename>.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>udev_rules</option></term>
              <listitem>
                <para>The name of the udev rules file or directory to look for files
                with the suffix <filename>.rules</filename>. Multiple rule files are
                read in lexical order. The default value is
                <filename>/etc/udev/rules.d</filename>.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>udev_log</option></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>
          <para>The udev rules are read from the files located in the
          <filename>/etc/udev/rules.d</filename> directory or at the location specified
          value in the configuraton file. Every line in the rules file contains at least
          one key value pair. There are two kind of keys, match and assignement keys.
          If all match keys are matching against its value, the rule gets applied and the
          assign keys get the specified value assigned. A matching rule may specify the
          name of the device node, add a symlink pointing to the node, or run a specified
          program as part of the event handling. If no matching rule is found, the default
          device node name is used.</para>

          <para>A rule may consists of a list of one or more key value pairs separated by
          a comma. Each key has a distinct operation, depending on the used operator. Valid
          operators are:</para>
          <variablelist>
            <varlistentry>
              <term><option>==</option></term>
              <listitem>
                <para>Compare for equality.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>!=</option></term>
              <listitem>
                <para>Compare for non-equality.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>=</option></term>
              <listitem>
                <para>Asign a value to a key. Keys that represent a list, are reset
                and only this single value is assigned.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>+=</option></term>
              <listitem>
                <para>Add the value to a key that holds a list of entries.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>:=</option></term>
              <listitem>
                <para>Assign  a  value  to  a key finally; disallow any later changes,
                which may be used to prevent changes by any later rules.</para>
              </listitem>
            </varlistentry>
          </variablelist>

          <para>The following key names can be used to match against device properties:</para>
          <variablelist>
            <varlistentry>
              <term><option>ACTION</option></term>
              <listitem>
                <para>Match the kernel action name.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>KERNEL</option></term>
              <listitem>
                <para>Match the kernel device name</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>DEVPATH</option></term>
              <listitem>
                <para>Match the kernel devpath.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>SUBSYSTEM</option></term>
              <listitem>
                <para>Match the kernel subsystem name</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>BUS</option></term>
              <listitem>
                <para>Match the typ of bus the device is connected to.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>DRIVER</option></term>
              <listitem>
                <para>Match the kernel driver name.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>ID</option></term>
              <listitem>
                <para>Match the device number on the bus.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>ENV{<replaceable>key</replaceable>}</option></term>
              <listitem>
                <para>Match against the value of an environment key. Depending on
                the specified operation, this key is also used as a assignment.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>SYSFS{<replaceable>filename</replaceable>}</option></term>
              <listitem>
                <para>Match the sysfs attribute value. Up to five values can be specified.
                Trailing whitespace is ignored, if the specified match value does not contain
                trailing whitespace itself.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>PROGRAM</option></term>
              <listitem>
                <para>Execute external program. The key is true, if the program returns
                without exit code zero. The whole event environment is available to the
                executed program. The program's output printed to stdout is available for
                the RESULT key.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>RESULT</option></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>
              </listitem>
            </varlistentry>
          </variablelist>

          <para>Most of the fields support a shell style pattern matching. The following
          pattern characters are supported:</para>
          <variablelist>
            <varlistentry>
              <term><option>*</option></term>
              <listitem>
                <para>Matches zero, or any number of characters.</para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><option>?</option></term>
              <listitem>
                <para>Matches any single character.</para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><option>[]</option></term>
              <listitem>
                <para>Matches any single character specified within the brackets.
                example, the pattern string 'tty[SR]' would match either 'ttyS' or 'ttyR'.
                Ranges are also supported within this match with the '-' character.
                For example, to match on the range of all digits, the pattern [0-9] would
                be used. If the first character following the '[' is a '!', any characters
                not enclosed are matched.</para>
              </listitem>
            </varlistentry>
          </variablelist>

          <para>The following keys can get values assigned:</para>
          <variablelist>
            <varlistentry>
              <term><option>NAME</option></term>
              <listitem>
                <para>The name of the node to be created, or the name, the network interface
                should be renamed to. Only one rule can set the a name, all later rules with
                a NAME key will be ignored.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>SYMLINK</option></term>
              <listitem>
                <para>The name of a symlink targeting the node. Every matching rule can add
                this value to the list of symlinks to be created along with the device  node.
                Multiple symlinks may be specified by separating the names by the space
                character.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>OWNER, GROUP, MODE</option></term>
              <listitem>
                <para>The permissions for the device node. Every specified value over writes
                the compiled-in default value.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>ENV{<replaceable>key</replaceable>}</option></term>
              <listitem>
                <para>Export the key to the environment. Depending on the specified
                operation, this key is also used as a match.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>RUN</option></term>
              <listitem>
                <para>Add a program to the list of programs to be executed for a specific
                device.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>LABEL</option></term>
              <listitem>
                <para>Named label where a GOTO can jump to.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>GOTO</option></term>
              <listitem>
                <para>Jumps to the next LABEL with a matching gname</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>IMPORT{<replaceable>type</replaceable>}</option></term>
              <listitem>
                <para>Import the printed result or the content of a file in environment key
                format into the event environment. <option>program</option> will execute an
                external program and read its output. <option>file</option> will inport a
                text file. If no option is given, udev will determine it from the  executable
                bit of of the file permissions.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>WAIT_FOR_SYSFS</option></term>
              <listitem>
                <para>Wait for the specified sysfs file of the device to be created. May be used
                to fight agains timing issues wth the kernel.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>OPTIONS</option></term>
              <listitem>
                <para><option>last_rule</option> stops further rules application. No later rules
                will have any effect.
                <option>ignore_device</option> will ignore this event completely.
                <option>ignore_remove</option> will ignore  any  later  remove  event  for  this
                device. This may be useful as a workaround for broken device drivers.
                <option>all_partitions</option> will create device nodes for all available partitions of
                a block device. This may be useful for removable media.</para>
              </listitem>
            </varlistentry>
          </variablelist>

          <para>The <option>NAME</option>, <option>SYMLINK</option>, <option>PROGRAM</option>,
          <option>OWNER</option>  and  <option>GROUP</option>  fields  support  simple
          printf-like string substitutions:</para>
          <variablelist>
            <varlistentry>
              <term><option>%k</option>, <option>$kernel</option></term>
              <listitem>
                <para>The kernel name for this device.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%b</option>, <option>$id</option></term>
              <listitem>
                <para>The kernel bus id for this device.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%n</option>, <option>$number</option></term>
              <listitem>
                <para>The kernel number for this device. For example, 'sda3' has
                kernel number of '3'</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%p</option>, <option>$devpath</option></term>
              <listitem>
                <para>The devpath of the device.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%s{<replaceable>file</replaceable>}</option>, <option>$sysfs{<replaceable>file</replaceable>}</option></term>
              <listitem>
                <para>The content of a sysfs attribute.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%e{<replaceable>key</replaceable>}</option>, <option>$env{<replaceable>key</replaceable>}</option></term>
              <listitem>
                <para>The value of an environment variable.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%m</option>, <option>$major</option></term>
              <listitem>
                <para>The kernel major number for the device.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%M</option> <option>$minor</option></term>
              <listitem>
                <para>The kernel minor number for the device.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%c</option>, <option>$result</option></term>
              <listitem>
                <para>The string returned by the external program requested with PROGRAM.
                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 '+' char this part plus all remaining parts
                of the result string are substituted: <option>%c{N+}</option></para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%e</option>, <option>$enum</option></term>
              <listitem>
                <para>If a device node already exists with the name, the smallest next free
                number is used. This  can be used to create compatibility symlinks and enumerate
                devices of the same type originating from different kernel subsystems.</para>
                <para>Note: The use of the enumeration facility is unreliable for events that
                request a number at the same time. The  use  of enumerations in todays setups
                where devices can come and go at any time is not recommended.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%P</option>, <option>$parent</option></term>
              <listitem>
                <para>The node name of the parent device.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%r</option>, <option>$root</option></term>
              <listitem>
                <para>The udev_root value.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%N</option>, <option>$tempnode</option></term>
              <listitem>
                <para>The name of a created temporary device node to provide access to
                the device from a external program before the real node is created.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>%%</option></term>
              <listitem>
              <para>The '%' character itself.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>$$</option></term>
              <listitem>
              <para>The '$' character itself.</para>
              </listitem>
            </varlistentry>
          </variablelist>
          <para>The count of characters to be substituted may be limited by specifying
          the format length value. For example, '%3s{file}' will only
          insert the first three characters of the sysfs attribute</para>
        </refsect2>
      </refsect1>

      <refsect1><title>ENVIRONMENT</title>
        <variablelist>
          <varlistentry>
            <term><option>ACTION</option></term>
            <listitem>
              <para><replaceable>add</replaceable> or <replaceable>remove</replaceable> signifies
              the addition or the removal of a device.</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term><option>DEVPATH</option></term>
            <listitem>
              <para>The sysfs devpath without the mountpoint but a leading slash.</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term><option>SUBSYSTEM</option></term>
            <listitem>
              <para>The kernel subsystem the device belongs to.</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term><option>UDEV_LOG</option></term>
            <listitem>
              <para>Overrides the syslog priority specified in the config file.</para>
            </listitem>
          </varlistentry>
        </variablelist>
     </refsect1>

      <refsect1><title>AUTHOR</title>
        <para>Written by Greg Kroah-Hartman <email>greg@kroah.com</email> and
        Kay Sievers <email>kay.sievers@vrfy.org</email>. With much help from
        Dan  Stekloff <email>dsteklof@us.ibm.com</email> and many others.</para>
      </refsect1>

      <refsect1>
        <title>SEE ALSO</title>
        <para><citerefentry>
            <refentrytitle>udev</refentrytitle><manvolnum>8</manvolnum>
          </citerefentry>, 
          <citerefentry>
            <refentrytitle>udevinfo</refentrytitle><manvolnum>8</manvolnum>
          </citerefentry>, 
          <citerefentry>
            <refentrytitle>udevd</refentrytitle><manvolnum>8</manvolnum>
          </citerefentry>, 
          <citerefentry>
            <refentrytitle>udevmonitor</refentrytitle><manvolnum>8</manvolnum>
        </citerefentry></para>
      </refsect1>
    </refentry>
  </section>
</article>