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1<?xml version='1.0' encoding="UTF-8"?> 1<?xml version='1.0' encoding="UTF-8"?>
2<!DOCTYPE guide SYSTEM "/dtd/guide.dtd"> 2<!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
3<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/udev-guide.xml,v 1.43 2007/10/18 18:31:06 nightmorph Exp $ --> 3<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/udev-guide.xml,v 1.44 2007/10/30 20:31:27 nightmorph Exp $ -->
4 4
5<guide link="/doc/en/udev-guide.xml"> 5<guide link="/doc/en/udev-guide.xml">
6<title>Gentoo udev Guide</title> 6<title>Gentoo udev Guide</title>
7 7
8<author title="Author"> 8<author title="Author">
9 <mail link="swift@gentoo.org">Sven Vermeulen</mail> 9 <mail link="swift@gentoo.org">Sven Vermeulen</mail>
10</author> 10</author>
11<author title="Contributor"> 11<author title="Contributor">
12 <mail link="greg_g@gentoo.org">Gregorio Guidi</mail> 12 <mail link="greg_g@gentoo.org">Gregorio Guidi</mail>
13</author> 13</author>
14<author title="Editor">
15 <mail link="nightmorph"/>
16</author>
14 17
15<abstract> 18<abstract>
16This document explains what udev is and how you can use udev to fit your needs. 19This document explains what udev is and how you can use udev to fit your needs.
17</abstract> 20</abstract>
18 21
19<!-- The content of this document is licensed under the CC-BY-SA license --> 22<!-- The content of this document is licensed under the CC-BY-SA license -->
20<!-- See http://creativecommons.org/licenses/by-sa/2.5 --> 23<!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
21<license/> 24<license/>
22 25
23<version>0.32</version> 26<version>0.33</version>
24<date>2007-08-02</date> 27<date>2007-10-30</date>
25 28
26<chapter> 29<chapter>
27<title>What is udev?</title> 30<title>What is udev?</title>
28<section> 31<section>
29<title>The /dev Directory</title> 32<title>The /dev Directory</title>
395</p> 398</p>
396 399
397</body> 400</body>
398</section> 401</section>
399<section> 402<section>
403<title>udev loads modules in an unpredictable order</title>
404<body>
405
406<p>
407Sometimes udev loads modules in an undesired, unpredictable, or seemingly random
408order. This is especially common for systems that have multiple devices of the
409same type, as well as multimedia devices. This can affect the assigned numbers
410of devices; for example, sound cards may sometimes swap numbers.
411</p>
412
413<p>
414There are a few solutions to fix device numbers and/or module load order.
415Ideally, you can just use module parameters to specify your desired device
416number. Some modules, such as ALSA, include the "index" parameter. Modules that
417use the index parameter can be adjusted as shown. This example is for a system
418with two sound cards. The card with an index of 0 is designated as the first
419card. Once the parameters are changed, the module config files must be updated.
420</p>
421
422<pre caption="Specifying module parameters">
423# <i>echo "option snd-ice1724 index=0" >> /etc/modules.d/alsa</i>
424# <i>echo "option snd-ymfpci index=1" >> /etc/modules.d/alsa</i>
425# <i>update-modules</i>
426</pre>
427
428<p>
429The above example is the preferred solution, but not all modules support
430parameters such as index. For these modules, you'll have to force the correct
431module load order. First, you must stop udev from autoloading the modules by
432blacklisting them. Be sure to use the exact name of the module being loaded.
433For PCI devices, you'll need to use the module names obtained from the output of
434<c>pcimodules</c>, available in the <c>pciutils</c> package. The following
435example uses DVB modules.
436</p>
437
438<pre caption="Blacklisting modules">
439# <i>echo "blacklist b2c2-flexcop-pci" >> /etc/modules.d/dvb</i>
440# <i>echo "blacklist budget" >> /etc/modules.d/dvb</i>
441# <i>update-modules</i>
442</pre>
443
444<p>
445Next, load the modules in the correct order. Add them to
446<path>/etc/modules.autoload.d/kernel-2.6</path> <e>in the exact order you want
447them loaded</e>.
448</p>
449
450<pre caption="Loading modules in the correct order">
451# <i>echo "budget" >> /etc/modules.autoload.d/kernel-2.6</i>
452# <i>echo "b2c2-flexcop-pci" >> /etc/modules.autoload.d/kernel-2.6</i>
453</pre>
454
455</body>
456</section>
457<section>
400<title>Other issues</title> 458<title>Other issues</title>
401<body> 459<body>
402 460
403<p> 461<p>
404If device nodes are not created when a module is loaded from 462If device nodes are not created when a module is loaded from

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