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UDEV(7) 			     udev			       UDEV(7)

       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
       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 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.

	   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:

	   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 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.
	   All attributes 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.

	   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 programs output printed to stdout is
	   available for 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

		   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

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

	   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 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.

       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

       $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.

       $root, %r
	   The udev_root value.

       $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), udevinfo(8), udevmonitor(8)

udev				  August 2005			       UDEV(7)

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