aboutsummaryrefslogtreecommitdiff
blob: 4a65dbebe80a81fa41dd8f939f61d4e4144eae6d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
'\" t
.\"     Title: udev
.\"    Author: Greg Kroah-Hartmann <greg@kroah.com>
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 03/08/2018
.\"    Manual: udev
.\"    Source: udev
.\"  Language: English
.\"
.TH "UDEV" "7" "" "udev" "udev"
.\" -----------------------------------------------------------------
.\" * Define some portability stuff
.\" -----------------------------------------------------------------
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.\" http://bugs.debian.org/507673
.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\" -----------------------------------------------------------------
.\" * set default formatting
.\" -----------------------------------------------------------------
.\" disable hyphenation
.nh
.\" disable justification (adjust text to left margin only)
.ad l
.\" -----------------------------------------------------------------
.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.SH "NAME"
udev \- Dynamic device management
.SH "DESCRIPTION"
.PP
udev supplies the system software with device events, manages permissions of device nodes and may create additional symlinks in the
/dev
directory, or renames network interfaces\&. The kernel usually just assigns unpredictable device names based on the order of discovery\&. Meaningful symlinks or network device names provide a way to reliably identify devices based on their properties or current configuration\&.
.PP
The udev daemon,
\fBudevd\fR(8), receives device uevents directly from the kernel whenever a device is added or removed from the system, or it changes its state\&. When udev receives a device event, it matches its configured set of rules against various device attributes to identify the device\&. Rules that match may provide additional device information to be stored in the udev database or to be used to create meaningful symlink names\&.
.PP
All device information udev processes is stored in the udev database and sent out to possible event subscribers\&. Access to all stored data and the event sources is provided by the library libudev\&.
.SH "RULES FILES"
.PP
The udev rules are read from the files located in the system rules directory
/lib/udev/rules\&.d, the volatile runtime directory
/run/udev/rules\&.d
and the local administration directory
/etc/udev/rules\&.d\&. All rules files are collectively sorted and processed in lexical order, regardless of the directories in which they live\&. However, files with identical filenames replace each other\&. Files in
/etc
have the highest priority, files in
/run
take precedence over files with the same name in
/lib\&. This can be used to override a system\-supplied rules file with a local file if needed; a symlink in
/etc
with the same name as a rules file in
/lib, pointing to
/dev/null, disables the rules file entirely\&. Rule files must have the extension
\&.rules; other extensions are ignored\&.
.PP
Every line in the rules file contains at least one key\-value pair\&. Except for empty lines or lines beginning with
#, which are ignored\&. There are two kinds of keys: match and assignment\&. If all match keys match against their values, the rule gets applied and the assignment keys get the specified values assigned\&.
.PP
A matching rule may rename a network interface, add symlinks pointing to the device node, or run a specified program as part of the event handling\&.
.PP
A rule consists of a comma\-separated list of one or more key\-value pairs\&. Each key has a distinct operation, depending on the used operator\&. Valid operators are:
.PP
==
.RS 4
Compare for equality\&.
.RE
.PP
!=
.RS 4
Compare for inequality\&.
.RE
.PP
=
.RS 4
Assign a value to a key\&. Keys that represent a list are reset and only this single value is assigned\&.
.RE
.PP
+=
.RS 4
Add the value to a key that holds a list of entries\&.
.RE
.PP
\-=
.RS 4
Remove the value from a key that holds a list of entries\&.
.RE
.PP
:=
.RS 4
Assign a value to a key finally; disallow any later changes\&.
.RE
.PP
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\&.
.PP
\fIACTION\fR
.RS 4
Match the name of the event action\&.
.RE
.PP
\fIDEVPATH\fR
.RS 4
Match the devpath of the event device\&.
.RE
.PP
\fIKERNEL\fR
.RS 4
Match the name of the event device\&.
.RE
.PP
\fINAME\fR
.RS 4
Match the name of a network interface\&. It can be used once the NAME key has been set in one of the preceding rules\&.
.RE
.PP
\fISYMLINK\fR
.RS 4
Match the name of a symlink targeting the node\&. It can be used once a SYMLINK key has been set in one of the preceding rules\&. There may be multiple symlinks; only one needs to match\&.
.RE
.PP
\fISUBSYSTEM\fR
.RS 4
Match the subsystem of the event device\&.
.RE
.PP
\fIDRIVER\fR
.RS 4
Match the driver name of the event device\&. Only set this key for devices which are bound to a driver at the time the event is generated\&.
.RE
.PP
\fIATTR{\fR\fI\fIfilename\fR\fR\fI}\fR, \fISYSCTL{\fR\fI\fIkernel parameter\fR\fR\fI}\fR
.RS 4
Match sysfs attribute values of the event device\&. Trailing whitespace in the attribute values is ignored unless the specified match value itself contains trailing whitespace\&.
Match a kernel parameter value\&.
.RE
.PP
\fIKERNELS\fR
.RS 4
Search the devpath upwards for a matching device name\&.
.RE
.PP
\fISUBSYSTEMS\fR
.RS 4
Search the devpath upwards for a matching device subsystem name\&.
.RE
.PP
\fIDRIVERS\fR
.RS 4
Search the devpath upwards for a matching device driver name\&.
.RE
.PP
\fIATTRS{\fR\fI\fIfilename\fR\fR\fI}\fR
.RS 4
Search the devpath upwards for a device with matching sysfs attribute values\&. If multiple
\fIATTRS\fR
matches are specified, all of them must match on the same device\&. Trailing whitespace in the attribute values is ignored unless the specified match value itself contains trailing whitespace\&.
.RE
.PP
\fITAGS\fR
.RS 4
Search the devpath upwards for a device with matching tag\&.
.RE
.PP
\fIENV{\fR\fI\fIkey\fR\fR\fI}\fR
.RS 4
Match against a device property value\&.
.RE
.PP
\fITAG\fR
.RS 4
Match against a device tag\&.
.RE
.PP
\fITEST{\fR\fI\fIoctal mode mask\fR\fR\fI}\fR
.RS 4
Test the existence of a file\&. An octal mode mask can be specified if needed\&.
.RE
.PP
\fIPROGRAM\fR
.RS 4
Execute a program to determine whether there is a match; the key is true if the program returns successfully\&. The device properties are made available to the executed program in the environment\&. The program\*(Aqs standard output is available in the
\fIRESULT\fR
key\&.
.sp
This can only be used for very short\-running foreground tasks\&. For details, see
\fIRUN\fR\&.
.RE
.PP
\fIRESULT\fR
.RS 4
Match the returned string of the last
\fIPROGRAM\fR
call\&. This key can be used in the same or in any later rule after a
\fIPROGRAM\fR
call\&.
.RE
.PP
Most of the fields support shell glob pattern matching and alternate patterns\&. The following special characters are supported:
.PP
*
.RS 4
Matches zero or more characters\&.
.RE
.PP
?
.RS 4
Matches any single character\&.
.RE
.PP
[]
.RS 4
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 via the
\-
character\&. For example, to match on the range of all digits, the pattern
[0\-9]
could be used\&. If the first character following the
[
is a
!, any characters not enclosed are matched\&.
.RE
.PP
|
.RS 4
Separates alternative patterns\&. For example, the pattern string
abc|x*
would match either
abc
or
x*\&.
.RE
.PP
The following keys can get values assigned:
.PP
\fINAME\fR
.RS 4
The name to use for a network interface\&. The name of a device node cannot be changed by udev, only additional symlinks can be created\&.
.RE
.PP
\fISYMLINK\fR
.RS 4
The name of a symlink targeting the node\&. Every matching rule adds this value to the list of symlinks to be created\&.
.sp
The set of characters to name a symlink is limited\&. Allowed characters are
0\-9A\-Za\-z#+\-\&.:=@_/, valid UTF\-8 character sequences, and
\ex00
hex encoding\&. All other characters are replaced by a
_
character\&.
.sp
Multiple symlinks may be specified by separating the names by the space character\&. In case multiple devices claim the same name, the link always points to the device with the highest link_priority\&. If the current device goes away, the links are re\-evaluated and the device with the next highest link_priority becomes the owner of the link\&. If no link_priority is specified, the order of the devices (and which one of them owns the link) is undefined\&.
.sp
Symlink names must never conflict with the kernel\*(Aqs default device node names, as that would result in unpredictable behavior\&.
.RE
.PP
\fIOWNER\fR, \fIGROUP\fR, \fIMODE\fR
.RS 4
The permissions for the device node\&. Every specified value overrides the compiled\-in default value\&.
.RE
.PP
\fISECLABEL{\fR\fI\fImodule\fR\fR\fI}\fR
.RS 4
Applies the specified Linux Security Module label to the device node\&.
.RE
.PP
\fIATTR{\fR\fI\fIkey\fR\fR\fI}\fR
.RS 4
The value that should be written to a sysfs attribute of the event device\&.
.RE
.PP
\fISYSCTL{\fR\fI\fIkernel parameter\fR\fR\fI}\fR
.RS 4
The value that should be written to kernel parameter\&.
.RE
.PP
\fIENV{\fR\fI\fIkey\fR\fR\fI}\fR
.RS 4
Set a device property value\&. Property names with a leading
\&.
are neither stored in the database nor exported to events or external tools (run by, for example, the
\fIPROGRAM\fR
match key)\&.
.RE
.PP
\fITAG\fR
.RS 4
Attach a tag to a device\&. This is used to filter events for users of libudev\*(Aqs monitor functionality, or to enumerate a group of tagged devices\&. The implementation can only work efficiently if only a few tags are attached to a device\&. It is only meant to be used in contexts with specific device filter requirements, and not as a general\-purpose flag\&. Excessive use might result in inefficient event handling\&.
.RE
.PP
\fIRUN{\fR\fI\fItype\fR\fR\fI}\fR
.RS 4
Add a program to the list of programs to be executed after processing all the rules for a specific event, depending on
type:
.PP
program
.RS 4
Execute an external program specified as the assigned value\&. If no absolute path is given, the program is expected to live in
/lib/udev, otherwise, the absolute path must be specified\&.
.sp
This is the default if no
\fItype\fR
is specified\&.
.RE
.PP
builtin
.RS 4
As
\fIprogram\fR, but use one of the built\-in programs rather than an external one\&.
.RE
.sp
The program name and following arguments are separated by spaces\&. Single quotes can be used to specify arguments with spaces\&.
.sp
This can only be used for very short\-running foreground tasks\&. Running an event process for a long period of time may block all further events for this or a dependent device\&.
.sp
Starting daemons or other long\-running processes is not appropriate for udev; the forked processes, detached or not, will be unconditionally killed after the event handling has finished\&.
.RE
.PP
\fILABEL\fR
.RS 4
A named label to which a
\fIGOTO\fR
may jump\&.
.RE
.PP
\fIGOTO\fR
.RS 4
Jumps to the next
\fILABEL\fR
with a matching name\&.
.RE
.PP
\fIIMPORT{\fR\fI\fItype\fR\fR\fI}\fR
.RS 4
Import a set of variables as device properties, depending on
type:
.PP
program
.RS 4
Execute an external program specified as the assigned value and import its output, which must be in environment key format\&. Path specification, command/argument separation, and quoting work like in
\fIRUN\fR\&.
.RE
.PP
builtin
.RS 4
Similar to
program, but use one of the built\-in programs rather than an external one\&.
.RE
.PP
file
.RS 4
Import a text file specified as the assigned value, the content of which must be in environment key format\&.
.RE
.PP
db
.RS 4
Import a single property specified as the assigned value from the current device database\&. This works only if the database is already populated by an earlier event\&.
.RE
.PP
cmdline
.RS 4
Import a single property from the kernel command line\&. For simple flags the value of the property is set to
1\&.
.RE
.PP
parent
.RS 4
Import the stored keys from the parent device by reading the database entry of the parent device\&. The value assigned to
\fBIMPORT{parent}\fR
is used as a filter of key names to import (with the same shell glob pattern matching used for comparisons)\&.
.RE
.sp
This can only be used for very short\-running foreground tasks\&. For details see
\fBRUN\fR\&.
.RE
.PP
\fIWAIT_FOR\fR
.RS 4
Wait for a file to become available or until a timeout of 10 seconds expires\&. The path is relative to the sysfs device; if no path is specified, this waits for an attribute to appear\&.
.RE
.PP
\fIOPTIONS\fR
.RS 4
Rule and device options:
.PP
\fBlink_priority=\fR\fB\fIvalue\fR\fR
.RS 4
Specify the priority of the created symlinks\&. Devices with higher priorities overwrite existing symlinks of other devices\&. The default is 0\&.
.RE
.PP
\fBstring_escape=\fR\fB\fInone|replace\fR\fR
.RS 4
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\&.
.RE
.PP
\fBstatic_node=\fR
.RS 4
Apply the permissions specified in this rule to the static device node with the specified name\&. Static device node creation can be requested by kernel modules\&. These nodes might not have a corresponding kernel device at the time udevd is started; they can trigger automatic kernel module loading\&.
.RE
.PP
\fBwatch\fR
.RS 4
Watch the device node with inotify; when the node is closed after being opened for writing, a change uevent is synthesized\&.
.RE
.PP
\fBnowatch\fR
.RS 4
Disable the watching of a device node with inotify\&.
.RE
.RE
.PP
The
\fINAME\fR,
\fISYMLINK\fR,
\fIPROGRAM\fR,
\fIOWNER\fR,
\fIGROUP\fR,
\fIMODE\fR, and
\fIRUN\fR
fields support simple string substitutions\&. The
\fIRUN\fR
substitutions are performed after all rules have been processed, right before the program is executed, allowing for the use of device properties set by earlier matching rules\&. For all other fields, substitutions are performed while the individual rule is being processed\&. The available substitutions are:
.PP
\fB$kernel\fR, \fB%k\fR
.RS 4
The kernel name for this device\&.
.RE
.PP
\fB$number\fR, \fB%n\fR
.RS 4
The kernel number for this device\&. For example,
sda3
has kernel number
3\&.
.RE
.PP
\fB$devpath\fR, \fB%p\fR
.RS 4
The devpath of the device\&.
.RE
.PP
\fB$id\fR, \fB%b\fR
.RS 4
The name of the device matched while searching the devpath upwards for
\fBSUBSYSTEMS\fR,
\fBKERNELS\fR,
\fBDRIVERS\fR, and
\fBATTRS\fR\&.
.RE
.PP
\fB$driver\fR
.RS 4
The driver name of the device matched while searching the devpath upwards for
\fBSUBSYSTEMS\fR,
\fBKERNELS\fR,
\fBDRIVERS\fR, and
\fBATTRS\fR\&.
.RE
.PP
\fB$attr{\fR\fB\fIfile\fR\fR\fB}\fR, \fB%s{\fR\fB\fIfile\fR\fR\fB}\fR
.RS 4
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, and a previous
\fBKERNELS\fR,
\fBSUBSYSTEMS\fR,
\fBDRIVERS\fR, or
\fBATTRS\fR
test selected a parent device, then the attribute from that parent device is used\&.
.sp
If the attribute is a symlink, the last element of the symlink target is returned as the value\&.
.RE
.PP
\fB$env{\fR\fB\fIkey\fR\fR\fB}\fR, \fB%E{\fR\fB\fIkey\fR\fR\fB}\fR
.RS 4
A device property value\&.
.RE
.PP
\fB$major\fR, \fB%M\fR
.RS 4
The kernel major number for the device\&.
.RE
.PP
\fB$minor\fR, \fB%m\fR
.RS 4
The kernel minor number for the device\&.
.RE
.PP
\fB$result\fR, \fB%c\fR
.RS 4
The string returned by the external program requested with
\fIPROGRAM\fR\&. 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
+
character, this part plus all remaining parts of the result string are substituted:
%c{N+}\&.
.RE
.PP
\fB$parent\fR, \fB%P\fR
.RS 4
The node name of the parent device\&.
.RE
.PP
\fB$name\fR
.RS 4
The current name of the device\&. If not changed by a rule, it is the name of the kernel device\&.
.RE
.PP
\fB$links\fR
.RS 4
A space\-separated list of the current symlinks\&. The value is only set during a remove event or if an earlier rule assigned a value\&.
.RE
.PP
\fB$sys\fR, \fB%S\fR
.RS 4
The sysfs mount point\&.
.RE
.PP
\fB$devnode\fR, \fB%N\fR
.RS 4
The name of the device node\&.
.RE
.PP
\fB%%\fR
.RS 4
The
%
character itself\&.
.RE
.PP
\fB$$\fR
.RS 4
The
$
character itself\&.
.RE
.SH "HARDWARE DATABASE FILES"
.PP
The hwdb files are read from the files located in the system hwdb directory
/usr/lib/udev/hwdb\&.d, the volatile runtime directory
/run/udev/hwdb\&.d
and the local administration directory
/etc/udev/hwdb\&.d\&. All hwdb files are collectively sorted and processed in lexical order, regardless of the directories in which they live\&. However, files with identical filenames replace each other\&. Files in
/etc
have the highest priority, files in
/run
take precedence over files with the same name in
/usr/lib\&. This can be used to override a system\-supplied hwdb file with a local file if needed; a symlink in
/etc
with the same name as a hwdb file in
/usr/lib, pointing to
/dev/null, disables the hwdb file entirely\&. hwdb files must have the extension
\&.hwdb; other extensions are ignored\&.
.PP
The hwdb file contains data records consisting of matches and associated key\-value pairs\&. Every record in the hwdb starts with one or more match string, specifying a shell glob to compare the database lookup string against\&. Multiple match lines are specified in additional consecutive lines\&. Every match line is compared indivdually, they are combined by OR\&. Every match line must start at the first character of the line\&.
.PP
The match lines are followed by one or more key\-value pair lines, which are recognized by a leading space character\&. The key name and value are separated by
=\&. An empty line signifies the end of a record\&. Lines beginning with
#
are ignored\&.
.PP
The content of all hwdb files is read by
\fBudevadm\fR(8)
and compiled to a binary database located at
/etc/udev/hwdb\&.bin, or alternatively
/usr/lib/udev/hwdb\&.bin
if you want ship the compiled database in an immutable image\&. During runtime only the binary database is used\&.
.SH "SEE ALSO"
.PP
\fBudevd\fR(8),
\fBudevadm\fR(8)