Provided by: udev_079-0ubuntu34_i386 bug


       udev - dynamic device management


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

       Usually udev runs as udevd(8) and receives uevents directly from the
       kernel if a device is added or removed form the system.

       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.


       All udev configuration files are placed in /etc/udev/*. Every file
       consist of a set of lines of text. All empty lines or lines beginning
       with ’#’ will be ignored.

   Configuration file
       udev expects its main configuration file at /etc/udev/udev.conf. It
       consists of a set of variables allowing the user to override default
       udev values. The following variables can be set:

              Specifies where to place the device nodes in the filesystem. The
              default value is /dev.

              The name of the udev rules file or directory to look for files
              with the suffix .rules. Multiple rule files are read in lexical
              order. The default value is /etc/udev/rules.d.

              The logging priority. Valid values are the numerical syslog
              priorities or their textual representations: err, info and

   Rules files
       The udev rules are read from the files located in the /etc/udev/rules.d
       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.

       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:

       ==     Compare for equality.

       !=     Compare for non-equality.

       =      Asign a value to a key. Keys that represent a list, are reset
              and only this single value is assigned.

       +=     Add the value to a key that holds a list of entries.

       :=     Assign a value to a key finally; disallow any later changes,
              which may be used to prevent changes by any later rules.

       The following key names can be used to match against device properties:

       ACTION Match the kernel action name.

       KERNEL Match the kernel device name

              Match the kernel devpath.

              Match the kernel subsystem name

       BUS    Match the typ of bus the device is connected to.

       DRIVER Match the kernel driver name.

       ID     Match the device number on the bus.

              Match against the value of an environment key. Depending on the
              specified operation, this key is also used as a assignment.

              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.

              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.

       RESULT 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.

       Most of the fields support a shell style pattern matching. The
       following pattern characters are supported:

       *      Matches zero, or any number of characters.

       ?      Matches any single character.

       []     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

       The following keys can get values assigned:

       NAME   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.

              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.

              The permissions for the device node. Every specified value over
              writes the compiled-in default value.

              Export the key to the environment. Depending on the specified
              operation, this key is also used as a match.

       RUN    Add a program to the list of programs to be executed for a
              specific device.

       LABEL  Named label where a GOTO can jump to.

       GOTO   Jumps to the next LABEL with a matching gname

              Import the printed result or the content of a file in
              environment key format into the event environment.  program will
              execute an external program and read its output.  file will
              inport a text file. If no option is given, udev will determine
              it from the executable bit of of the file permissions.

              Wait for the specified sysfs file of the device to be created.
              May be used to fight agains timing issues wth the kernel.

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

       The NAME, SYMLINK, PROGRAM, OWNER and GROUP fields support simple
       printf-like string substitutions:

       %k, $kernel
              The kernel name for this device.

       %b, $id
              The kernel bus id for this device.

       %n, $number
              The kernel number for this device. For example, ’sda3’ has
              kernel number of ’3’

       %p, $devpath
              The devpath of the device.

       %s{file}, $sysfs{file}
              The content of a sysfs attribute.

       %E{key}, $env{key}
              The value of an environment variable.

       %m, $major
              The kernel major number for the device.

       %M $minor
              The kernel minor number for the device.

       %c, $result
              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: %c{N}. If the number is followed by the ’+’ char this
              part plus all remaining parts of the result string are
              substituted: %c{N+}

       %P, $parent
              The node name of the parent device.

       %r, $root
              The udev_root value.

       %N, $tempnode
              The name of a created temporary device node to provide access to
              the device from a external program before the real node is

       %%     The ’%’ character itself.

       $$     The ’$’ character itself.

       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


       ACTION add or remove signifies the addition or the removal of a device.

              The sysfs devpath without the mountpoint but a leading slash.

              The kernel subsystem the device belongs to.

              Overrides the syslog priority specified in the config file.


       Written by Greg Kroah-Hartman <> and Kay Sievers
       <>. With much help from Dan Stekloff
       <> and many others.


       udev(8), udevinfo(8), udevd(8), udevmonitor(8)