udev.xml

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   2 <!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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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>PROGRAM</option></term>
 229               <listitem>
 230                 <para>Execute external program. The key is true, if the program returns
 231                 with exit code zero. The whole event environment is available to the
 232                 executed program. The program's output printed to stdout, is available in
 233                 the RESULT key.</para>
 234               </listitem>
 235             </varlistentry>
 236
 237             <varlistentry>
 238               <term><option>RESULT</option></term>
 239               <listitem>
 240                 <para>Match the returned string of the last PROGRAM call. This key can
 241                 be used in the same or in any later rule after a PROGRAM call.</para>
 242               </listitem>
 243             </varlistentry>
 244           </variablelist>
 245
 246           <para>Most of the fields support a shell style pattern matching. The following
 247           pattern characters are supported:</para>
 248           <variablelist>
 249             <varlistentry>
 250               <term><option>*</option></term>
 251               <listitem>
 252                 <para>Matches zero, or any number of characters.</para>
 253               </listitem>
 254             </varlistentry>
 255             <varlistentry>
 256               <term><option>?</option></term>
 257               <listitem>
 258                 <para>Matches any single character.</para>
 259               </listitem>
 260             </varlistentry>
 261             <varlistentry>
 262               <term><option>[]</option></term>
 263               <listitem>
 264                 <para>Matches any single character specified within the brackets. For
 265                 example, the pattern string 'tty[SR]' would match either 'ttyS' or 'ttyR'.
 266                 Ranges are also supported within this match with the '-' character.
 267                 For example, to match on the range of all digits, the pattern [0-9] would
 268                 be used. If the first character following the '[' is a '!', any characters
 269                 not enclosed are matched.</para>
 270               </listitem>
 271             </varlistentry>
 272           </variablelist>
 273
 274           <para>The following keys can get values assigned:</para>
 275           <variablelist>
 276             <varlistentry>
 277               <term><option>NAME</option></term>
 278               <listitem>
 279                 <para>The name of the node to be created, or the name the network interface
 280                 should be renamed to. Only one rule can set the node name, all later rules with
 281                 a NAME key will be ignored.</para>
 282               </listitem>
 283             </varlistentry>
 284
 285             <varlistentry>
 286               <term><option>SYMLINK</option></term>
 287               <listitem>
 288                 <para>The name of a symlink targeting the node. Every matching rule can add
 289                 this value to the list of symlinks to be created along with the device  node.
 290                 Multiple symlinks may be specified by separating the names by the space
 291                 character.</para>
 292               </listitem>
 293             </varlistentry>
 294
 295             <varlistentry>
 296               <term><option>OWNER, GROUP, MODE</option></term>
 297               <listitem>
 298                 <para>The permissions for the device node. Every specified value overwrites
 299                 the compiled-in default value.</para>
 300               </listitem>
 301             </varlistentry>
 302
 303             <varlistentry>
 304               <term><option>ATTR{<replaceable>key</replaceable>}</option></term>
 305               <listitem>
 306                 <para>The value that should be written to a sysfs attribute of the
 307                 event device. Depending on the type of operator, this key is also
 308                 used to match against the value of a sysfs attribute.</para>
 309               </listitem>
 310             </varlistentry>
 311
 312             <varlistentry>
 313               <term><option>ENV{<replaceable>key</replaceable>}</option></term>
 314               <listitem>
 315                 <para>Export a variable to the environment. Depending on the type of operator,
 316                 this key is also to match against an environment variable.</para>
 317               </listitem>
 318             </varlistentry>
 319
 320             <varlistentry>
 321               <term><option>RUN</option></term>
 322               <listitem>
 323                 <para>Add a program to the list of programs to be executed for a specific
 324                 device. This can only be used for very short running tasks. Running an
 325                 event process for a long period of time may block all further events for
 326                 this or a dependent device. Long running tasks need to be immediately
 327                 detached from the event process itself.</para>
 328               </listitem>
 329             </varlistentry>
 330
 331             <varlistentry>
 332               <term><option>LABEL</option></term>
 333               <listitem>
 334                 <para>Named label where a GOTO can jump to.</para>
 335               </listitem>
 336             </varlistentry>
 337
 338             <varlistentry>
 339               <term><option>GOTO</option></term>
 340               <listitem>
 341                 <para>Jumps to the next LABEL with a matching name</para>
 342               </listitem>
 343             </varlistentry>
 344
 345             <varlistentry>
 346               <term><option>IMPORT{<replaceable>type</replaceable>}</option></term>
 347               <listitem>
 348                 <para>Import a set of variables into the event environment,
 349                 depending on <replaceable>type</replaceable>:</para>
 350                 <variablelist>
 351                   <varlistentry>
 352                     <term><option>program</option></term>
 353                     <listitem>
 354                       <para>Execute an external program specified as the assigned value and
 355                       import its output, which must be in environment key format.</para>
 356                     </listitem>
 357                   </varlistentry>
 358                   <varlistentry>
 359                     <term><option>file</option></term>
 360                     <listitem>
 361                       <para>Import a text file specified as the assigned value, which must be in
 362                       environment key format.</para>
 363                     </listitem>
 364                   </varlistentry>
 365                   <varlistentry>
 366                     <term><option>parent</option></term>
 367                     <listitem>
 368                       <para>Import the stored keys from the parent device by reading
 369                       the database entry of the parent device. The value assigned to
 370                       <option>IMPORT{parent}</option> is used as a filter of key names
 371                       to import (with the same shell-style pattern matching used for
 372                       comparisons).</para>
 373                     </listitem>
 374                   </varlistentry>
 375                 </variablelist>
 376                 <para>If no option is given, udev will choose between <option>program</option>
 377                 and <option>file</option> based on the executable bit of the file
 378                 permissions.</para>
 379               </listitem>
 380             </varlistentry>
 381
 382             <varlistentry>
 383               <term><option>WAIT_FOR_SYSFS</option></term>
 384               <listitem>
 385                 <para>Wait for the specified sysfs file of the device to be created. Can be used
 386                 to fight against kernel sysfs timing issues.</para>
 387               </listitem>
 388             </varlistentry>
 389
 390             <varlistentry>
 391               <term><option>OPTIONS</option></term>
 392               <listitem>
 393                 <para><option>last_rule</option> stops further rules application. No later rules
 394                 will have any effect.
 395                 <option>ignore_device</option> will ignore this event completely.
 396                 <option>ignore_remove</option> will ignore  any  later  remove  event  for  this
 397                 device. This may be useful as a workaround for broken device drivers.
 398                 <option>all_partitions</option> will create the device nodes for all available
 399                 partitions of a block device. This may be useful for removable media devices where
 400                 media changes are not detected.</para>
 401               </listitem>
 402             </varlistentry>
 403           </variablelist>
 404
 405           <para>The <option>NAME</option>, <option>SYMLINK</option>, <option>PROGRAM</option>,
 406           <option>OWNER</option>, <option>GROUP</option>  and  <option>RUN</option>
 407           fields support simple printf-like string substitutions. The <option>RUN</option>
 408           format chars gets applied after all rules have been processed, right before the program
 409           is executed. It allows the use of the complete environment set by earlier matching
 410           rules. For all other fields, substitutions are applied while the individual rule is
 411           being processed. The available substitutions are:</para>
 412           <variablelist>
 413             <varlistentry>
 414               <term><option>$kernel</option>, <option>%k</option></term>
 415               <listitem>
 416                 <para>The kernel name for this device.</para>
 417               </listitem>
 418             </varlistentry>
 419
 420             <varlistentry>
 421               <term><option>$number</option>, <option>%n</option></term>
 422               <listitem>
 423                 <para>The kernel number for this device. For example, 'sda3' has
 424                 kernel number of '3'</para>
 425               </listitem>
 426             </varlistentry>
 427
 428             <varlistentry>
 429               <term><option>$devpath</option>, <option>%p</option></term>
 430               <listitem>
 431                 <para>The devpath of the device.</para>
 432               </listitem>
 433             </varlistentry>
 434
 435             <varlistentry>
 436               <term><option>$id</option>, <option>%b</option></term>
 437               <listitem>
 438                 <para>The name of the device matched while searching the devpath upwards for
 439                   <option>SUBSYSTEMS</option>, <option>KERNELS</option>, <option>DRIVERS</option> and <option>ATTRS</option>.
 440                 </para>
 441               </listitem>
 442             </varlistentry>
 443
 444             <varlistentry>
 445               <term><option>$attr{<replaceable>file</replaceable>}</option>, <option>%s{<replaceable>file</replaceable>}</option></term>
 446               <listitem>
 447                 <para>The value of a sysfs attribute found at the device, where
 448                 all keys of the rule have matched. If the matching device does not have
 449                 such an attribute, all devices along the chain of parents are searched
 450                 for a matching attribute.
 451                 If the attribute is a symlink, the last element of the symlink target is
 452                 returned as the value.</para>
 453               </listitem>
 454             </varlistentry>
 455
 456             <varlistentry>
 457               <term><option>$env{<replaceable>key</replaceable>}</option>, <option>%E{<replaceable>key</replaceable>}</option></term>
 458               <listitem>
 459                 <para>The value of an environment variable.</para>
 460               </listitem>
 461             </varlistentry>
 462
 463             <varlistentry>
 464               <term><option>$major</option>, <option>%M</option></term>
 465               <listitem>
 466                 <para>The kernel major number for the device.</para>
 467               </listitem>
 468             </varlistentry>
 469
 470             <varlistentry>
 471               <term><option>$minor</option>, <option>%m</option></term>
 472               <listitem>
 473                 <para>The kernel minor number for the device.</para>
 474               </listitem>
 475             </varlistentry>
 476
 477             <varlistentry>
 478               <term><option>$result</option>, <option>%c</option></term>
 479               <listitem>
 480                 <para>The string returned by the external program requested with PROGRAM.
 481                 A single part of the string, separated by a space character may be selected
 482                 by specifying the part number as an attribute: <option>%c{N}</option>.
 483                 If the number is followed by the '+' char this part plus all remaining parts
 484                 of the result string are substituted: <option>%c{N+}</option></para>
 485               </listitem>
 486             </varlistentry>
 487
 488             <varlistentry>
 489               <term><option>$parent</option>, <option>%P</option></term>
 490               <listitem>
 491                 <para>The node name of the parent device.</para>
 492               </listitem>
 493             </varlistentry>
 494
 495             <varlistentry>
 496               <term><option>$root</option>, <option>%r</option></term>
 497               <listitem>
 498                 <para>The udev_root value.</para>
 499               </listitem>
 500             </varlistentry>
 501
 502             <varlistentry>
 503               <term><option>$tempnode</option>, <option>%N</option></term>
 504               <listitem>
 505                 <para>The name of a created temporary device node to provide access to
 506                 the device from a external program before the real node is created.</para>
 507               </listitem>
 508             </varlistentry>
 509
 510             <varlistentry>
 511               <term><option>%%</option></term>
 512               <listitem>
 513               <para>The '%' character itself.</para>
 514               </listitem>
 515             </varlistentry>
 516
 517             <varlistentry>
 518               <term><option>$$</option></term>
 519               <listitem>
 520               <para>The '$' character itself.</para>
 521               </listitem>
 522             </varlistentry>
 523           </variablelist>
 524           <para>The count of characters to be substituted may be limited by specifying
 525           the format length value. For example, '%3s{file}' will only
 526           insert the first three characters of the sysfs attribute</para>
 527         </refsect2>
 528       </refsect1>
 529
 530       <refsect1><title>AUTHOR</title>
 531         <para>Written by Greg Kroah-Hartman <email>greg@kroah.com</email> and
 532         Kay Sievers <email>kay.sievers@vrfy.org</email>. With much help from
 533         Dan  Stekloff <email>dsteklof@us.ibm.com</email> and many others.</para>
 534       </refsect1>
 535
 536       <refsect1>
 537         <title>SEE ALSO</title>
 538         <para><citerefentry>
 539             <refentrytitle>udevd</refentrytitle><manvolnum>8</manvolnum>
 540           </citerefentry>,
 541           <citerefentry>
 542             <refentrytitle>udevinfo</refentrytitle><manvolnum>8</manvolnum>
 543           </citerefentry>,
 544           <citerefentry>
 545             <refentrytitle>udevmonitor</refentrytitle><manvolnum>8</manvolnum>
 546         </citerefentry></para>
 547       </refsect1>
 548     </refentry>
 549   </section>
 550 </article>