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11 <date>August 2005</date>
12 <productname>udev</productname>
16 <refentrytitle>udev</refentrytitle>
17 <manvolnum>7</manvolnum>
18 <refmiscinfo class="version"></refmiscinfo>
22 <refname>udev</refname>
23 <refpurpose>dynamic device management</refpurpose>
26 <refsect1><title>DESCRIPTION</title>
27 <para>udev provides a dynamic device directory containing only the files for
28 actually present devices. It creates or removes device node files in the
29 <filename>/dev</filename> directory, or it renames network interfaces.</para>
31 <para>Usually udev runs as <citerefentry><refentrytitle>udevd</refentrytitle>
32 <manvolnum>8</manvolnum></citerefentry> and receives uevents directly from the
33 kernel if a device is added or removed from the system.</para>
35 <para>If udev receives a device event, it matches its configured rules
36 against the available device attributes provided in sysfs to identify the device.
37 Rules that match may provide additional device information or specify a device
38 node name and multiple symlink names and instruct udev to run additional programs
39 as part of the device event handling.</para>
42 <refsect1><title>CONFIGURATION</title>
43 <para>All udev configuration files are placed in <filename>/etc/udev/*</filename>.
44 Every file consists of a set of lines of text. All empty lines or lines beginning
45 with '#' will be ignored.</para>
47 <refsect2><title>Configuration file</title>
48 <para>udev expects its main configuration file at <filename>/etc/udev/udev.conf</filename>.
49 It consists of a set of variables allowing the user to override default udev values.
50 The following variables can be set:</para>
53 <term><option>udev_root</option></term>
55 <para>Specifies where to place the device nodes in the filesystem.
56 The default value is <filename>/dev</filename>.</para>
61 <term><option>udev_rules</option></term>
63 <para>The name of the udev rules file or directory to look for files
64 with the suffix <filename>.rules</filename>. Multiple rule files are
65 read in lexical order. The default value is
66 <filename>/etc/udev/rules.d</filename>.</para>
71 <term><option>udev_log</option></term>
73 <para>The logging priority. Valid values are the numerical syslog priorities
74 or their textual representations: <option>err</option>, <option>info</option>
75 and <option>debug</option>.</para>
81 <refsect2><title>Rules files</title>
82 <para>The udev rules are read from the files located in the
83 <filename>/etc/udev/rules.d</filename> directory or at the location specified
84 value in the configuration file. Every line in the rules file contains at least
85 one key value pair. There are two kind of keys, match and assignment keys.
86 If all match keys are matching against its value, the rule gets applied and the
87 assign keys get the specified value assigned.</para>
89 <para>A matching rule may specify the name of the device node, add a symlink
90 pointing to the node, or run a specified program as part of the event handling.
91 If no matching rule is found, the default device node name is used.</para>
93 <para>A rule may consist of a list of one or more key value pairs separated by
94 a comma. Each key has a distinct operation, depending on the used operator. Valid
98 <term><option>==</option></term>
100 <para>Compare for equality.</para>
105 <term><option>!=</option></term>
107 <para>Compare for non-equality.</para>
112 <term><option>=</option></term>
114 <para>Assign a value to a key. Keys that represent a list, are reset
115 and only this single value is assigned.</para>
120 <term><option>+=</option></term>
122 <para>Add the value to a key that holds a list of entries.</para>
127 <term><option>:=</option></term>
129 <para>Assign a value to a key finally; disallow any later changes,
130 which may be used to prevent changes by any later rules.</para>
135 <para>The following key names can be used to match against device properties.
136 Some of the keys also match against properties of the parent devices in sysfs,
137 not only the device that has generated the event. If multiple keys that match
138 a parent device are specified in a single rule, all these keys must match at
139 one and the same parent device.</para>
142 <term><option>ACTION</option></term>
144 <para>Match the name of the event action.</para>
149 <term><option>DEVPATH</option></term>
151 <para>Match the devpath of the event device.</para>
156 <term><option>KERNEL</option></term>
158 <para>Match the name of the event device.</para>
163 <term><option>NAME</option></term>
165 <para>Match the name of the node or network interface. It can
166 be used once the NAME key has been set in one of the preceding
172 <term><option>SUBSYSTEM</option></term>
174 <para>Match the subsystem of the event device.</para>
178 <term><option>DRIVER</option></term>
180 <para>Match the driver name of the event device. Only set for devices
181 which are bound to a driver at the time the event is generated.</para>
185 <term><option>ATTR{<replaceable>filename</replaceable>}</option></term>
187 <para>Match sysfs attribute values of the event device. Up to five
188 <option>ATTR</option> keys can be specified per rule. Trailing
189 whitespace in the attribute values is ignored, if the specified match
190 value does not contain trailing whitespace itself. Depending on the type
191 of operator, this key is also used to set the value of a sysfs attribute.
197 <term><option>KERNELS</option></term>
199 <para>Search the devpath upwards for a matching device name.</para>
204 <term><option>SUBSYSTEMS</option></term>
206 <para>Search the devpath upwards for a matching device subsystem name.</para>
211 <term><option>DRIVERS</option></term>
213 <para>Search the devpath upwards for a matching device driver name.</para>
218 <term><option>ATTRS{<replaceable>filename</replaceable>}</option></term>
220 <para>Search the devpath upwards for a device with matching sysfs attribute values.
221 Up to five <option>ATTRS</option> keys can be specified per rule, but all of them
222 must match on the same device. Trailing whitespace in the attribute values is ignored,
223 if the specified match value does not contain trailing whitespace itself.</para>
228 <term><option>ENV{<replaceable>key</replaceable>}</option></term>
230 <para>Match against the value of an environment variable. Up to five <option>ENV</option>
231 keys can be specified per rule. Depending on the type of operator, this key is also used
232 to export a variable to the environment.</para>
237 <term><option>TEST{<replaceable>octal mode mask</replaceable>}</option></term>
239 <para>Test the existence of a file. An octal mode mask can be specified
245 <term><option>PROGRAM</option></term>
247 <para>Execute external program. The key is true, if the program returns
248 with exit code zero. The whole event environment is available to the
249 executed program. The program's output printed to stdout, is available in
250 the RESULT key.</para>
255 <term><option>RESULT</option></term>
257 <para>Match the returned string of the last PROGRAM call. This key can
258 be used in the same or in any later rule after a PROGRAM call.</para>
263 <para>Most of the fields support a shell style pattern matching. The following
264 pattern characters are supported:</para>
267 <term><option>*</option></term>
269 <para>Matches zero, or any number of characters.</para>
273 <term><option>?</option></term>
275 <para>Matches any single character.</para>
279 <term><option>[]</option></term>
281 <para>Matches any single character specified within the brackets. For
282 example, the pattern string 'tty[SR]' would match either 'ttyS' or 'ttyR'.
283 Ranges are also supported within this match with the '-' character.
284 For example, to match on the range of all digits, the pattern [0-9] would
285 be used. If the first character following the '[' is a '!', any characters
286 not enclosed are matched.</para>
291 <para>The following keys can get values assigned:</para>
294 <term><option>NAME</option></term>
296 <para>The name of the node to be created, or the name the network interface
297 should be renamed to. Only one rule can set the node name, all later rules with
298 a NAME key will be ignored.</para>
303 <term><option>SYMLINK</option></term>
305 <para>The name of a symlink targeting the node. Every matching rule can add
306 this value to the list of symlinks to be created along with the device node.
307 Multiple symlinks may be specified by separating the names by the space
313 <term><option>OWNER, GROUP, MODE</option></term>
315 <para>The permissions for the device node. Every specified value overwrites
316 the compiled-in default value.</para>
321 <term><option>ATTR{<replaceable>key</replaceable>}</option></term>
323 <para>The value that should be written to a sysfs attribute of the
324 event device. Depending on the type of operator, this key is also
325 used to match against the value of a sysfs attribute.</para>
330 <term><option>ENV{<replaceable>key</replaceable>}</option></term>
332 <para>Export a variable to the environment. Depending on the type of operator,
333 this key is also to match against an environment variable.</para>
338 <term><option>RUN</option></term>
340 <para>Add a program to the list of programs to be executed for a specific
341 device. This can only be used for very short running tasks. Running an
342 event process for a long period of time may block all further events for
343 this or a dependent device. Long running tasks need to be immediately
344 detached from the event process itself.</para>
345 <para>If the specifiefd string starts with
346 <option>socket:<replaceable>path</replaceable></option>, all current event
347 values will be passed to the specified socket, as a message in the same
348 format the kernel sends an uevent. If the first character of the specified path
349 is an @ character, an abstract namespace socket is used, instead of an existing
355 <term><option>LABEL</option></term>
357 <para>Named label where a GOTO can jump to.</para>
362 <term><option>GOTO</option></term>
364 <para>Jumps to the next LABEL with a matching name</para>
369 <term><option>IMPORT{<replaceable>type</replaceable>}</option></term>
371 <para>Import a set of variables into the event environment,
372 depending on <replaceable>type</replaceable>:</para>
375 <term><option>program</option></term>
377 <para>Execute an external program specified as the assigned value and
378 import its output, which must be in environment key format.</para>
382 <term><option>file</option></term>
384 <para>Import a text file specified as the assigned value, which must be in
385 environment key format.</para>
389 <term><option>parent</option></term>
391 <para>Import the stored keys from the parent device by reading
392 the database entry of the parent device. The value assigned to
393 <option>IMPORT{parent}</option> is used as a filter of key names
394 to import (with the same shell-style pattern matching used for
399 <para>If no option is given, udev will choose between <option>program</option>
400 and <option>file</option> based on the executable bit of the file
406 <term><option>WAIT_FOR</option></term>
408 <para>Wait for a file to become available.</para>
413 <term><option>OPTIONS</option></term>
415 <para>Rule and device options:</para>
418 <term><option>last_rule</option></term>
420 <para>Stops further rules application. No later rules will have
425 <term><option>ignore_device</option></term>
427 <para>Ignore this event completely.</para>
431 <term><option>ignore_remove</option></term>
433 <para>Do not remove the device node when the device goes away. This may be
434 useful as a workaround for broken device drivers.</para>
438 <term><option>link_priority=<replaceable>value</replaceable></option></term>
440 <para>Specify the priority of the created symlinks. Devices with higher
441 priorities overwrite existing symlinks of other devices.</para>
445 <term><option>all_partitions</option></term>
447 <para>Create the device nodes for all available partitions of a block device.
448 This may be useful for removable media devices where media changes are not
453 <term><option>event_timeout=</option></term>
455 <para>Number of seconds an event will wait for operations to finish, before it
456 will terminate itself.</para>
460 <term><option>string_escape=<replaceable>none|replace</replaceable></option></term>
462 <para>Usually control and other possibly unsafe characters are replaced
463 in strings used for device naming. The mode of replacement can be specified
464 with this option.</para>
472 <para>The <option>NAME</option>, <option>SYMLINK</option>, <option>PROGRAM</option>,
473 <option>OWNER</option>, <option>GROUP</option>, <option>MODE</option> and <option>RUN</option>
474 fields support simple printf-like string substitutions. The <option>RUN</option>
475 format chars gets applied after all rules have been processed, right before the program
476 is executed. It allows the use of the complete environment set by earlier matching
477 rules. For all other fields, substitutions are applied while the individual rule is
478 being processed. The available substitutions are:</para>
481 <term><option>$kernel</option>, <option>%k</option></term>
483 <para>The kernel name for this device.</para>
488 <term><option>$number</option>, <option>%n</option></term>
490 <para>The kernel number for this device. For example, 'sda3' has
491 kernel number of '3'</para>
496 <term><option>$devpath</option>, <option>%p</option></term>
498 <para>The devpath of the device.</para>
503 <term><option>$id</option>, <option>%b</option></term>
505 <para>The name of the device matched while searching the devpath upwards for
506 <option>SUBSYSTEMS</option>, <option>KERNELS</option>, <option>DRIVERS</option> and <option>ATTRS</option>.
512 <term><option>$driver</option></term>
514 <para>The driver name of the device matched while searching the devpath upwards for
515 <option>SUBSYSTEMS</option>, <option>KERNELS</option>, <option>DRIVERS</option> and <option>ATTRS</option>.
521 <term><option>$attr{<replaceable>file</replaceable>}</option>, <option>%s{<replaceable>file</replaceable>}</option></term>
523 <para>The value of a sysfs attribute found at the device, where
524 all keys of the rule have matched. If the matching device does not have
525 such an attribute, follow the chain of parent devices and use the value
526 of the first attribute that matches.
527 If the attribute is a symlink, the last element of the symlink target is
528 returned as the value.</para>
533 <term><option>$env{<replaceable>key</replaceable>}</option>, <option>%E{<replaceable>key</replaceable>}</option></term>
535 <para>The value of an environment variable.</para>
540 <term><option>$major</option>, <option>%M</option></term>
542 <para>The kernel major number for the device.</para>
547 <term><option>$minor</option>, <option>%m</option></term>
549 <para>The kernel minor number for the device.</para>
554 <term><option>$result</option>, <option>%c</option></term>
556 <para>The string returned by the external program requested with PROGRAM.
557 A single part of the string, separated by a space character may be selected
558 by specifying the part number as an attribute: <option>%c{N}</option>.
559 If the number is followed by the '+' char this part plus all remaining parts
560 of the result string are substituted: <option>%c{N+}</option></para>
565 <term><option>$parent</option>, <option>%P</option></term>
567 <para>The node name of the parent device.</para>
572 <term><option>$name</option></term>
574 <para>The current name of the device node. If not changed by a rule, it is the
575 name of the kernel device.</para>
580 <term><option>$links</option></term>
582 <para>The current list of symlinks, separated by a space character. The value is
583 only set if an earlier rule assigned a value, or during a remove events.</para>
588 <term><option>$root</option>, <option>%r</option></term>
590 <para>The udev_root value.</para>
595 <term><option>$sys</option>, <option>%S</option></term>
597 <para>The sysfs mount point.</para>
602 <term><option>$tempnode</option>, <option>%N</option></term>
604 <para>The name of a created temporary device node to provide access to
605 the device from a external program before the real node is created.</para>
610 <term><option>%%</option></term>
612 <para>The '%' character itself.</para>
617 <term><option>$$</option></term>
619 <para>The '$' character itself.</para>
623 <para>The count of characters to be substituted may be limited by specifying
624 the format length value. For example, '%3s{file}' will only
625 insert the first three characters of the sysfs attribute</para>
629 <refsect1><title>AUTHOR</title>
630 <para>Written by Greg Kroah-Hartman <email>greg@kroah.com</email> and
631 Kay Sievers <email>kay.sievers@vrfy.org</email>. With much help from
632 Dan Stekloff and many others.</para>
636 <title>SEE ALSO</title>
638 <refentrytitle>udevd</refentrytitle><manvolnum>8</manvolnum>
641 <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
642 </citerefentry></para>