Provided by: udev_117-8_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 from 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
       consists 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 debug.

   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 configuration file.
       Every line in the rules file contains at least one key value pair.
       There are two kind of keys, match and assignment 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

       A rule may consist 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.

           Assign 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.
       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.

           Match the name of the event action.

           Match the devpath of the event device.

           Match the name of the event device.

           Match the subsystem of the event device.

           Match the driver name of the event device. Only set for devices
           which are bound to a driver at the time the event is generated.

           Match sysfs attribute values of the event device. Up to five ATTR
           keys can be specified per rule. Trailing whitespace in the
           attribute values is ignored, if the specified match value does not
           contain trailing whitespace itself. Depending on the type of
           operator, this key is also used to set the value of a sysfs

           Search the devpath upwards for a matching device name.

           Search the devpath upwards for a matching device subsystem name.

           Search the devpath upwards for a matching device driver name.

           Search the devpath upwards for a device with matching sysfs
           attribute values. Up to five ATTRS keys can be specified per rule,
           but all of them must match on the same device. Trailing whitespace
           in the attribute values is ignored, if the specified match value
           does not contain trailing whitespace itself.

           Match against the value of an environment variable. Up to five ENV
           keys can be specified per rule. Depending on the type of operator,
           this key is also used to export a variable to the environment.

       TEST{octal mode mask}
           Test the existence of a file. An octal mode mask can be specified
           if needed.

           Execute external program. The key is true, if the program returns
           with exit code zero. The whole event environment is available to
           the executed program. The program´s output printed to stdout, is
           available in the RESULT key.

           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. For
           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.

       The following keys can get values assigned:

           The name of the node to be created, or the name the network
           interface should be renamed to. Only one rule can set the node
           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
           overwrites the compiled-in default value.

           The value that should be written to a sysfs attribute of the event
           device. Depending on the type of operator, this key is also used to
           match against the value of a sysfs attribute.

           Export a variable to the environment. Depending on the type of
           operator, this key is also to match against an environment

           Add a program to the list of programs to be executed for a specific
           device. This can only be used for very short running tasks. Running
           an event process for a long period of time may block all further
           events for this or a dependent device. Long running tasks need to
           be immediately detached from the event process itself.

           Named label where a GOTO can jump to.

           Jumps to the next LABEL with a matching name

           Import a set of variables into the event environment, depending on

               Execute an external program specified as the assigned value and
               import its output, which must be in environment key format.

               Import a text file specified as the assigned value, which must
               be in environment key format.

               Import the stored keys from the parent device by reading the
               database entry of the parent device. The value assigned to
               IMPORT{parent} is used as a filter of key names to import (with
               the same shell-style pattern matching used for comparisons).

           If no option is given, udev will choose between program and file
           based on the executable bit of the file permissions.

           Wait for the specified sysfs file of the device to be created. Can
           be used to fight against kernel sysfs timing issues.

           Rule and device options:

               Stops further rules application. No later rules will have any

               Ignore this event completely.

               Do not remove the device node when the device goes away. This
               may be useful as a workaround for broken device drivers.

               Specify the priority of the created symlinks. Devices with
               higher priorities overwrite existing symlinks of other devices.

               Create the device nodes for all available partitions of a block
               device. This may be useful for removable media devices where
               media changes are not detected.

               Usually control and other possibly unsafe characters are
               replaced in strings used for device naming. The mode of
               replacement can be specified with this option.

       The NAME, SYMLINK, PROGRAM, OWNER, GROUP and RUN fields support simple
       printf-like string substitutions. The RUN format chars gets applied
       after all rules have been processed, right before the program is
       executed. It allows the use of the complete environment set by earlier
       matching rules. For all other fields, substitutions are applied while
       the individual rule is being processed. The available substitutions

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

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

       $devpath, %p
           The devpath of the device.

       $id, %b
           The name of the device matched while searching the devpath upwards

           The driver name of the device matched while searching the devpath
           upwards for SUBSYSTEMS, KERNELS, DRIVERS and ATTRS.

       $attr{file}, %s{file}
           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, all devices along the chain of parents are searched
           for a matching attribute. If the attribute is a symlink, the last
           element of the symlink target is returned as the value.

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

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

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

       $result, %c
           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+}

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

           The name of the device node. The value is only set if an earlier
           rule assigned a value, or during a remove events.

       $root, %r
           The udev_root value.

       $sys, %S
           The sysfs mount point.

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

           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


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


       udevd(8), udevadm(8)