1<?xml version='1.0'?> 2<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" 3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> 4 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