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5<article>
6  <section>
7    <title>udev</title>
8    <refentry>
9      <refentryinfo>
10        <title>udev</title>
11        <date>August 2005</date>
12        <productname>udev</productname>
13      </refentryinfo>
14
15      <refmeta>
16        <refentrytitle>udev</refentrytitle>
17        <manvolnum>7</manvolnum>
18        <refmiscinfo class="version"></refmiscinfo>
19      </refmeta>
20
21      <refnamediv>
22        <refname>udev</refname>
23        <refpurpose>dynamic device management</refpurpose>
24      </refnamediv>
25
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>
30
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>
34
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>
40      </refsect1>
41
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>
46
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>
51          <variablelist>
52            <varlistentry>
53              <term><option>udev_root</option></term>
54              <listitem>
55                <para>Specifies where to place the device nodes in the filesystem.
56                The default value is <filename>/dev</filename>.</para>
57              </listitem>
58            </varlistentry>
59
60            <varlistentry>
61              <term><option>udev_rules</option></term>
62              <listitem>
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>
67              </listitem>
68            </varlistentry>
69
70            <varlistentry>
71              <term><option>udev_log</option></term>
72              <listitem>
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>
76              </listitem>
77            </varlistentry>
78          </variablelist>
79        </refsect2>
80
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>
88
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>
92
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
95          operators are:</para>
96          <variablelist>
97            <varlistentry>
98              <term><option>==</option></term>
99              <listitem>
100                <para>Compare for equality.</para>
101              </listitem>
102            </varlistentry>
103
104            <varlistentry>
105              <term><option>!=</option></term>
106              <listitem>
107                <para>Compare for non-equality.</para>
108              </listitem>
109            </varlistentry>
110
111            <varlistentry>
112              <term><option>=</option></term>
113              <listitem>
114                <para>Assign a value to a key. Keys that represent a list, are reset
115                and only this single value is assigned.</para>
116              </listitem>
117            </varlistentry>
118
119            <varlistentry>
120              <term><option>+=</option></term>
121              <listitem>
122                <para>Add the value to a key that holds a list of entries.</para>
123              </listitem>
124            </varlistentry>
125
126            <varlistentry>
127              <term><option>:=</option></term>
128              <listitem>
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>
131              </listitem>
132            </varlistentry>
133          </variablelist>
134
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>
140          <variablelist>
141            <varlistentry>
142              <term><option>ACTION</option></term>
143              <listitem>
144                <para>Match the name of the event action.</para>
145              </listitem>
146            </varlistentry>
147
148            <varlistentry>
149              <term><option>DEVPATH</option></term>
150              <listitem>
151                <para>Match the devpath of the event device.</para>
152              </listitem>
153            </varlistentry>
154
155            <varlistentry>
156              <term><option>KERNEL</option></term>
157              <listitem>
158                <para>Match the name of the event device.</para>
159              </listitem>
160            </varlistentry>
161
162            <varlistentry>
163              <term><option>SUBSYSTEM</option></term>
164              <listitem>
165                <para>Match the subsystem of the event device.</para>
166              </listitem>
167            </varlistentry>
168            <varlistentry>
169              <term><option>DRIVER</option></term>
170              <listitem>
171                <para>Match the driver name of the event device. Only set for devices
172                which are bound to a driver at the time the event is generated.</para>
173              </listitem>
174            </varlistentry>
175            <varlistentry>
176              <term><option>ATTR{<replaceable>filename</replaceable>}</option></term>
177              <listitem>
178                <para>Match sysfs attribute values of the event device. Up to five
179                <option>ATTR</option> keys can be specified per rule. Trailing
180                whitespace in the attribute values is ignored, if the specified match
181                value does not contain trailing whitespace itself. Depending on the type
182                of operator, this key is also used to set the value of a sysfs attribute.
183                </para>
184              </listitem>
185            </varlistentry>
186
187            <varlistentry>
188              <term><option>KERNELS</option></term>
189              <listitem>
190                <para>Search the devpath upwards for a matching device name.</para>
191              </listitem>
192            </varlistentry>
193
194            <varlistentry>
195              <term><option>SUBSYSTEMS</option></term>
196              <listitem>
197                <para>Search the devpath upwards for a matching device subsystem name.</para>
198              </listitem>
199            </varlistentry>
200
201            <varlistentry>
202              <term><option>DRIVERS</option></term>
203              <listitem>
204                <para>Search the devpath upwards for a matching device driver name.</para>
205              </listitem>
206            </varlistentry>
207
208            <varlistentry>
209              <term><option>ATTRS{<replaceable>filename</replaceable>}</option></term>
210              <listitem>
211                <para>Search the devpath upwards for a device with matching sysfs attribute values.
212                Up to five <option>ATTRS</option> keys can be specified per rule, but all of them
213                must match on the same device. Trailing whitespace in the attribute values is ignored,
214                if the specified match value does not contain trailing whitespace itself.</para>
215              </listitem>
216            </varlistentry>
217
218            <varlistentry>
219              <term><option>ENV{<replaceable>key</replaceable>}</option></term>
220              <listitem>
221                <para>Match against the value of an environment variable. Up to five <option>ENV</option>
222                keys can be specified per rule. Depending on the type of operator, this key is also used
223                to export a variable to the environment.</para>
224              </listitem>
225            </varlistentry>
226
227            <varlistentry>
228              <term><option>TEST{<replaceable>octal mode mask</replaceable>}</option></term>
229              <listitem>
230                <para>Test the existence of a file. An octal mode mask can be specified
231                if needed.</para>
232              </listitem>
233            </varlistentry>
234
235            <varlistentry>
236              <term><option>PROGRAM</option></term>
237              <listitem>
238                <para>Execute external program. The key is true, if the program returns
239                with exit code zero. The whole event environment is available to the
240                executed program. The program's output printed to stdout, is available in
241                the RESULT key.</para>
242              </listitem>
243            </varlistentry>
244
245            <varlistentry>
246              <term><option>RESULT</option></term>
247              <listitem>
248                <para>Match the returned string of the last PROGRAM call. This key can
249                be used in the same or in any later rule after a PROGRAM call.</para>
250              </listitem>
251            </varlistentry>
252          </variablelist>
253
254          <para>Most of the fields support a shell style pattern matching. The following
255          pattern characters are supported:</para>
256          <variablelist>
257            <varlistentry>
258              <term><option>*</option></term>
259              <listitem>
260                <para>Matches zero, or any number of characters.</para>
261              </listitem>
262            </varlistentry>
263            <varlistentry>
264              <term><option>?</option></term>
265              <listitem>
266                <para>Matches any single character.</para>
267              </listitem>
268            </varlistentry>
269            <varlistentry>
270              <term><option>[]</option></term>
271              <listitem>
272                <para>Matches any single character specified within the brackets. For
273                example, the pattern string 'tty[SR]' would match either 'ttyS' or 'ttyR'.
274                Ranges are also supported within this match with the '-' character.
275                For example, to match on the range of all digits, the pattern [0-9] would
276                be used. If the first character following the '[' is a '!', any characters
277                not enclosed are matched.</para>
278              </listitem>
279            </varlistentry>
280          </variablelist>
281
282          <para>The following keys can get values assigned:</para>
283          <variablelist>
284            <varlistentry>
285              <term><option>NAME</option></term>
286              <listitem>
287                <para>The name of the node to be created, or the name the network interface
288                should be renamed to. Only one rule can set the node name, all later rules with
289                a NAME key will be ignored.</para>
290              </listitem>
291            </varlistentry>
292
293            <varlistentry>
294              <term><option>SYMLINK</option></term>
295              <listitem>
296                <para>The name of a symlink targeting the node. Every matching rule can add
297                this value to the list of symlinks to be created along with the device  node.
298                Multiple symlinks may be specified by separating the names by the space
299                character.</para>
300              </listitem>
301            </varlistentry>
302
303            <varlistentry>
304              <term><option>OWNER, GROUP, MODE</option></term>
305              <listitem>
306                <para>The permissions for the device node. Every specified value overwrites
307                the compiled-in default value.</para>
308              </listitem>
309            </varlistentry>
310
311            <varlistentry>
312              <term><option>ATTR{<replaceable>key</replaceable>}</option></term>
313              <listitem>
314                <para>The value that should be written to a sysfs attribute of the
315                event device. Depending on the type of operator, this key is also
316                used to match against the value of a sysfs attribute.</para>
317              </listitem>
318            </varlistentry>
319
320            <varlistentry>
321              <term><option>ENV{<replaceable>key</replaceable>}</option></term>
322              <listitem>
323                <para>Export a variable to the environment. Depending on the type of operator,
324                this key is also to match against an environment variable.</para>
325              </listitem>
326            </varlistentry>
327
328            <varlistentry>
329              <term><option>RUN</option></term>
330              <listitem>
331                <para>Add a program to the list of programs to be executed for a specific
332                device. This can only be used for very short running tasks. Running an
333                event process for a long period of time may block all further events for
334                this or a dependent device. Long running tasks need to be immediately
335                detached from the event process itself.</para>
336              </listitem>
337            </varlistentry>
338
339            <varlistentry>
340              <term><option>LABEL</option></term>
341              <listitem>
342                <para>Named label where a GOTO can jump to.</para>
343              </listitem>
344            </varlistentry>
345
346            <varlistentry>
347              <term><option>GOTO</option></term>
348              <listitem>
349                <para>Jumps to the next LABEL with a matching name</para>
350              </listitem>
351            </varlistentry>
352
353            <varlistentry>
354              <term><option>IMPORT{<replaceable>type</replaceable>}</option></term>
355              <listitem>
356                <para>Import a set of variables into the event environment,
357                depending on <replaceable>type</replaceable>:</para>
358                <variablelist>
359                  <varlistentry>
360                    <term><option>program</option></term>
361                    <listitem>
362                      <para>Execute an external program specified as the assigned value and
363                      import its output, which must be in environment key format.</para>
364                    </listitem>
365                  </varlistentry>
366                  <varlistentry>
367                    <term><option>file</option></term>
368                    <listitem>
369                      <para>Import a text file specified as the assigned value, which must be in
370                      environment key format.</para>
371                    </listitem>
372                  </varlistentry>
373                  <varlistentry>
374                    <term><option>parent</option></term>
375                    <listitem>
376                      <para>Import the stored keys from the parent device by reading
377                      the database entry of the parent device. The value assigned to
378                      <option>IMPORT{parent}</option> is used as a filter of key names
379                      to import (with the same shell-style pattern matching used for
380                      comparisons).</para>
381                    </listitem>
382                  </varlistentry>
383                </variablelist>
384                <para>If no option is given, udev will choose between <option>program</option>
385                and <option>file</option> based on the executable bit of the file
386                permissions.</para>
387              </listitem>
388            </varlistentry>
389
390            <varlistentry>
391              <term><option>WAIT_FOR_SYSFS</option></term>
392              <listitem>
393                <para>Wait for the specified sysfs file of the device to be created. Can be used
394                to fight against kernel sysfs timing issues.</para>
395              </listitem>
396            </varlistentry>
397
398            <varlistentry>
399              <term><option>OPTIONS</option></term>
400              <listitem>
401                <para>Rule and device options:</para>
402                <variablelist>
403                  <varlistentry>
404                    <term><option>last_rule</option></term>
405                    <listitem>
406                      <para>Stops further rules application. No later rules will have
407                      any effect.</para>
408                    </listitem>
409                  </varlistentry>
410                  <varlistentry>
411                    <term><option>ignore_device</option></term>
412                    <listitem>
413                      <para>Ignore this event completely.</para>
414                    </listitem>
415                  </varlistentry>
416                  <varlistentry>
417                    <term><option>ignore_remove</option></term>
418                    <listitem>
419                      <para>Ignore any later remove event for this device. This may be useful
420                      as a workaround for broken device drivers.</para>
421                    </listitem>
422                  </varlistentry>
423                  <varlistentry>
424                    <term><option>link_priority=<replaceable>value</replaceable></option></term>
425                    <listitem>
426                      <para>Specify the priority of the created symlinks. Devices with higher
427                      priorities overwrite existing symlinks of other devices.</para>
428                    </listitem>
429                  </varlistentry>
430                  <varlistentry>
431                    <term><option>all_partitions</option></term>
432                    <listitem>
433                      <para>Create the device nodes for all available partitions of a block device.
434                      This may be useful for removable media devices where media changes are not
435                      detected.</para>
436                    </listitem>
437                  </varlistentry>
438                  <varlistentry>
439                    <term><option>string_escape=<replaceable>none|replace</replaceable></option></term>
440                    <listitem>
441                      <para>Usually control and other possibly unsafe characters are replaced
442                      in strings used for device naming. The mode of replacement can be specified
443                      with this option.</para>
444                    </listitem>
445                  </varlistentry>
446                </variablelist>
447              </listitem>
448            </varlistentry>
449          </variablelist>
450
451          <para>The <option>NAME</option>, <option>SYMLINK</option>, <option>PROGRAM</option>,
452          <option>OWNER</option>, <option>GROUP</option>  and  <option>RUN</option>
453          fields support simple printf-like string substitutions. The <option>RUN</option>
454          format chars gets applied after all rules have been processed, right before the program
455          is executed. It allows the use of the complete environment set by earlier matching
456          rules. For all other fields, substitutions are applied while the individual rule is
457          being processed. The available substitutions are:</para>
458          <variablelist>
459            <varlistentry>
460              <term><option>$kernel</option>, <option>%k</option></term>
461              <listitem>
462                <para>The kernel name for this device.</para>
463              </listitem>
464            </varlistentry>
465
466            <varlistentry>
467              <term><option>$number</option>, <option>%n</option></term>
468              <listitem>
469                <para>The kernel number for this device. For example, 'sda3' has
470                kernel number of '3'</para>
471              </listitem>
472            </varlistentry>
473
474            <varlistentry>
475              <term><option>$devpath</option>, <option>%p</option></term>
476              <listitem>
477                <para>The devpath of the device.</para>
478              </listitem>
479            </varlistentry>
480
481            <varlistentry>
482              <term><option>$id</option>, <option>%b</option></term>
483              <listitem>
484                <para>The name of the device matched while searching the devpath upwards for
485                  <option>SUBSYSTEMS</option>, <option>KERNELS</option>, <option>DRIVERS</option> and <option>ATTRS</option>.
486                </para>
487              </listitem>
488            </varlistentry>
489
490            <varlistentry>
491              <term><option>$attr{<replaceable>file</replaceable>}</option>, <option>%s{<replaceable>file</replaceable>}</option></term>
492              <listitem>
493                <para>The value of a sysfs attribute found at the device, where
494                all keys of the rule have matched. If the matching device does not have
495                such an attribute, all devices along the chain of parents are searched
496                for a matching attribute.
497                If the attribute is a symlink, the last element of the symlink target is
498                returned as the value.</para>
499              </listitem>
500            </varlistentry>
501
502            <varlistentry>
503              <term><option>$env{<replaceable>key</replaceable>}</option>, <option>%E{<replaceable>key</replaceable>}</option></term>
504              <listitem>
505                <para>The value of an environment variable.</para>
506              </listitem>
507            </varlistentry>
508
509            <varlistentry>
510              <term><option>$major</option>, <option>%M</option></term>
511              <listitem>
512                <para>The kernel major number for the device.</para>
513              </listitem>
514            </varlistentry>
515
516            <varlistentry>
517              <term><option>$minor</option>, <option>%m</option></term>
518              <listitem>
519                <para>The kernel minor number for the device.</para>
520              </listitem>
521            </varlistentry>
522
523            <varlistentry>
524              <term><option>$result</option>, <option>%c</option></term>
525              <listitem>
526                <para>The string returned by the external program requested with PROGRAM.
527                A single part of the string, separated by a space character may be selected
528                by specifying the part number as an attribute: <option>%c{N}</option>.
529                If the number is followed by the '+' char this part plus all remaining parts
530                of the result string are substituted: <option>%c{N+}</option></para>
531              </listitem>
532            </varlistentry>
533
534            <varlistentry>
535              <term><option>$parent</option>, <option>%P</option></term>
536              <listitem>
537                <para>The node name of the parent device.</para>
538              </listitem>
539            </varlistentry>
540
541            <varlistentry>
542              <term><option>$root</option>, <option>%r</option></term>
543              <listitem>
544                <para>The udev_root value.</para>
545              </listitem>
546            </varlistentry>
547
548            <varlistentry>
549              <term><option>$sys</option>, <option>%S</option></term>
550              <listitem>
551                <para>The sysfs mount point.</para>
552              </listitem>
553            </varlistentry>
554
555            <varlistentry>
556              <term><option>$tempnode</option>, <option>%N</option></term>
557              <listitem>
558                <para>The name of a created temporary device node to provide access to
559                the device from a external program before the real node is created.</para>
560              </listitem>
561            </varlistentry>
562
563            <varlistentry>
564              <term><option>%%</option></term>
565              <listitem>
566              <para>The '%' character itself.</para>
567              </listitem>
568            </varlistentry>
569
570            <varlistentry>
571              <term><option>$$</option></term>
572              <listitem>
573              <para>The '$' character itself.</para>
574              </listitem>
575            </varlistentry>
576          </variablelist>
577          <para>The count of characters to be substituted may be limited by specifying
578          the format length value. For example, '%3s{file}' will only
579          insert the first three characters of the sysfs attribute</para>
580        </refsect2>
581      </refsect1>
582
583      <refsect1><title>AUTHOR</title>
584        <para>Written by Greg Kroah-Hartman <email>greg@kroah.com</email> and
585        Kay Sievers <email>kay.sievers@vrfy.org</email>. With much help from
586        Dan  Stekloff <email>dsteklof@us.ibm.com</email> and many others.</para>
587      </refsect1>
588
589      <refsect1>
590        <title>SEE ALSO</title>
591        <para><citerefentry>
592            <refentrytitle>udevd</refentrytitle><manvolnum>8</manvolnum>
593          </citerefentry>, 
594          <citerefentry>
595            <refentrytitle>udevinfo</refentrytitle><manvolnum>8</manvolnum>
596          </citerefentry>, 
597          <citerefentry>
598            <refentrytitle>udevmonitor</refentrytitle><manvolnum>8</manvolnum>
599        </citerefentry></para>
600      </refsect1>
601    </refentry>
602  </section>
603</article>
604