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Remove all references to coldplug, bug 170679. All hail the udev-only era, for as long as it lasts. Don't like udev? Complain to greg_kh! udev is now The Gentoo Way(tm)

1 swift 1.1 <?xml version='1.0' encoding="UTF-8"?>
2     <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
3 neysx 1.4
4 nightmorph 1.38 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/udev-guide.xml,v 1.37 2007/02/26 08:58:04 nightmorph Exp $ -->
5 neysx 1.4
6 swift 1.1 <guide link="/doc/en/udev-guide.xml">
7     <title>Gentoo udev Guide</title>
8    
9     <author title="Author">
10 nightmorph 1.34 <mail link="swift@gentoo.org">Sven Vermeulen</mail>
11 swift 1.8 </author>
12     <author title="Contributor">
13 neysx 1.24 <mail link="greg_g@gentoo.org">Gregorio Guidi</mail>
14 swift 1.1 </author>
15    
16     <abstract>
17     This document explains what udev is and how you can use udev to fit your needs.
18     </abstract>
19    
20     <license/>
21    
22 nightmorph 1.38 <version>0.28</version>
23     <date>2007-03-12</date>
24 swift 1.1
25     <chapter>
26     <title>What is udev?</title>
27     <section>
28     <title>The /dev Directory</title>
29     <body>
30    
31     <p>
32     When Linux-users talk about the hardware on their system in the vicinity of
33 swift 1.3 people who believe Linux is some sort of virus or brand of coffee, the use of
34 swift 1.1 "slash dev slash foo" will return a strange look for sure. But for the fortunate
35     user (and that includes you) using <path>/dev/hda1</path> is just a fast way of
36     explaining that we are talking about the primary master IDE, first partition. Or
37     aren't we?
38     </p>
39    
40     <p>
41     We all know what a device file is. Some even know why device files have special
42     numbers when we take a closer look at them when we issue <c>ls -l</c> in
43     <path>/dev</path>. But what we always take for granted is that the primary
44     master IDE disk is referred to as <path>/dev/hda</path>. You might not see it
45     this way, but this is a flaw by design.
46     </p>
47    
48     <p>
49 swift 1.3 Think about hotpluggable devices like USB, IEEE1394, hot-swappable PCI, ... What
50     is the first device? And for how long? What will the other devices be named when
51 swift 1.1 the first one disappears? How will that affect ongoing transactions? Wouldn't it
52 swift 1.3 be fun that a printing job is suddenly moved from your supernew laserprinter to
53 swift 1.1 your almost-dead matrix printer because your mom decided to pull the plug of the
54 swift 1.20 laserprinter which happened to be the first printer?
55 swift 1.1 </p>
56    
57     <p>
58     Enter <e>udev</e>. The goals of the udev project are both interesting and
59     needed:
60     </p>
61    
62     <ul>
63 swift 1.3 <li>Runs in userspace</li>
64     <li>Dynamically creates/removes device files</li>
65     <li>Provides consistent naming</li>
66     <li>Provides a user-space API</li>
67 swift 1.1 </ul>
68    
69     <p>
70     To provide these features, udev is developed in three separate projects:
71     <e>namedev</e>, <e>libsysfs</e> and, of course, <e>udev</e>.
72     </p>
73    
74     </body>
75     </section>
76     <section>
77     <title>namedev</title>
78     <body>
79    
80     <p>
81     Namedev allows you to define the device naming separately from the udev program.
82     This allows for flexible naming policies and naming schemes developed by
83     separate entities. This device naming subsystem provides a standard interface
84     that udev can use.
85     </p>
86    
87     <p>
88     Currently only a single naming scheme is provided by namedev; the one provided
89 swift 1.3 by LANANA, used by the majority of Linux systems currently and therefore very
90 swift 1.1 suitable for the majority of Linux users.
91     </p>
92    
93     <p>
94     Namedev uses a 5-step procedure to find out the name of a given device. If the
95     device name is found in one of the given steps, that name is used. The steps
96     are:
97     </p>
98    
99     <ul>
100     <li>label or serial number</li>
101     <li>bus device number</li>
102     <li>bus topology</li>
103     <li>statically given name</li>
104     <li>kernel provided name</li>
105     </ul>
106    
107     <p>
108     The <e>label or serial number</e> step checks if the device has a unique
109     identifier. For instance USB devices have a unique USB serial number; SCSI
110     devices have a unique UUID. If namedev finds a match between this unique number
111     and a given configuration file, the name provided in the configuration file is
112     used.
113     </p>
114    
115     <p>
116     The <e>bus device number</e> step checks the device bus number. For
117     non-hot-swappable environments this procedure is sufficient to
118     identify a hardware device. For instance PCI bus numbers rarely change in the
119     lifetime of a system. Again, if namedev finds a match between this position and
120     a given configuration file, the name provided in that configuration file is
121     used.
122     </p>
123    
124     <p>
125     Likewise the <e>bus topology</e> is a rather static way of defining devices as
126     long as the user doesn't switch devices. When the position of the device matches
127 swift 1.3 a given setting provided by the user, the accompanying name is used.
128 swift 1.1 </p>
129    
130     <p>
131     The fourth step, <e>statically given name</e>, is a simple string replacement.
132     When the kernel name (the default name) matches a given replacement string, the
133     substitute name will be used.
134     </p>
135    
136     <p>
137     The final step (<e>kernel provided name</e>) is a catch-all: this one takes
138     the default name provided by the kernel. In the majority of cases this is
139     sufficient as it matches the device naming used on current Linux systems.
140     </p>
141    
142     </body>
143     </section>
144     <section>
145     <title>libsysfs</title>
146     <body>
147    
148     <p>
149     udev interacts with the kernel through the sysfs pseudo filesystem. The libsysfs
150     project provides a common API to access the information given by the sysfs
151     filesystem in a generic way. This allows for querying all kinds of hardware
152     without having to make assumptions on the kind of hardware.
153     </p>
154    
155     </body>
156     </section>
157     <section>
158     <title>udev</title>
159     <body>
160    
161     <p>
162     Every time the kernel notices an update in the device structure, it calls the
163     <path>/sbin/hotplug</path> program. Hotplug runs the applications linked in the
164     <path>/etc/hotplug.d/default</path> directory where you will also find a symlink
165     to the udev application. Hotplug directs the information given by the kernel to
166     the udev application which performs the necessary actions on the
167     <path>/dev</path> structure (creating or deleting device files).
168     </p>
169    
170     </body>
171     </section>
172     </chapter>
173    
174     <chapter>
175     <title>Using udev on Gentoo</title>
176     <section>
177     <title>Requirements</title>
178     <body>
179    
180     <p>
181 swift 1.8 udev is meant to be used in combination with a 2.6 kernel (like
182 nightmorph 1.37 <c>gentoo-sources</c> with the default 2005.0 profile). If you're using such a
183     kernel then you just have to make sure that you have a recent
184     <c>sys-apps/baselayout</c> version. That's all you need.
185 swift 1.1 </p>
186    
187 swift 1.8 <pre caption="Installing udev">
188     # <i>emerge udev</i>
189 swift 1.1 </pre>
190    
191     <p>
192 nightmorph 1.30 udev will install <c>hotplug-base</c> as one of its dependencies. You do not
193     need to install <c>hotplug</c> unless you want your modules automatically
194     loaded when you plug devices in. <c>hotplug</c> also handles the automated
195     bringup of network devices and firmware downloading.
196 swift 1.1 </p>
197    
198 swift 1.8 <pre caption="Installing optional hotplug scripts">
199     # <i>emerge hotplug</i>
200 swift 1.1 </pre>
201    
202     <p>
203 swift 1.21 Kernelwise, be sure to activate the following options:
204 swift 1.1 </p>
205    
206     <pre caption="Required kernel options">
207 swift 1.6 General setup ---&gt;
208 swift 1.1 [*] Support for hot-pluggable devices
209    
210     File systems ---&gt;
211     Pseudo filesystems ---&gt;
212     [*] /proc file system support
213     [*] Virtual memory file system support (former shm fs)
214     </pre>
215    
216     <p>
217     You can leave the <c>/dev file system support (OBSOLETE)</c> active if you
218 swift 1.16 wish but you have to make sure that "Automatically mount at boot" is disabled:
219 swift 1.1 </p>
220    
221 swift 1.16 <pre caption="Don't automatically mount devfsd">
222     File systems ---&gt;
223     Pseudo Filesystems ---&gt;
224     [*] /dev file system support (OBSOLETE)
225     [ ] Automatically mount at boot
226     </pre>
227    
228 swift 1.21 <p>
229     If you use <c>genkernel</c>, don't forget to run it with the <c>--udev</c>
230     option to enable all the required kernel configuration directives. The default
231     configuration given by this <c>genkernel</c> invocation is sufficient.
232     </p>
233    
234 swift 1.1 </body>
235     </section>
236     <section>
237     <title>Configuration</title>
238     <body>
239    
240     <p>
241 neysx 1.5 If you want to use the udev-tweaks Gentoo added to make your life
242 swift 1.15 comfortable, then read no more. Gentoo will use udev but keep a static
243     <path>/dev</path> so that you will never have any missing device nodes.
244     The Gentoo init scripts won't run the devfsd daemon and will deactivate devfs
245     when you boot up.
246 swift 1.1 </p>
247    
248     <p>
249     But if you are a die-hard and want to run a udev-only, no-tweaked system as is
250 swift 1.2 intended by the udev development (including the difficulties of missing device
251     nodes because udev doesn't support them yet), by all means, read on :)
252 swift 1.1 </p>
253    
254     <p>
255 bennyc 1.13 We'll deactivate the rules that save the device file nodes: edit the
256 swift 1.2 <c>RC_DEVICE_TARBALL</c> variable in <path>/etc/conf.d/rc</path> and set it to
257     <c>no</c>:
258     </p>
259 swift 1.1
260 swift 1.2 <pre caption="/etc/conf.d/rc">
261     RC_DEVICE_TARBALL="no"
262 swift 1.1 </pre>
263    
264     <p>
265 swift 1.8 If you have included devfs support in your kernel, you can deactivate it in
266 swift 1.14 the bootloader configuration: add <c>gentoo=nodevfs</c> as a kernel parameter.
267     If you want to use devfs and deactivate udev, add <c>gentoo=noudev</c> as kernel
268 swift 1.8 parameter.
269     </p>
270    
271     </body>
272     </section>
273     </chapter>
274    
275     <chapter>
276     <title>Known Issues</title>
277     <section>
278     <title>Missing device node files at boot</title>
279     <body>
280    
281     <p>
282 neysx 1.9 If you can't boot successfully because you get an error about
283 swift 1.8 <path>/dev/null</path> not found, or because the initial console is missing, the
284     problem is that you lack some device files that must be available <e>before</e>
285     <path>/dev</path> is mounted and handled by udev. This is common on Gentoo
286     machines installed from old media.
287     </p>
288    
289     <p>
290     If you run <c>sys-apps/baselayout-1.8.12</c> or later, this problem is
291     alleviated since the boot process should still manage to complete. However, to
292 swift 1.10 get rid of those annoying warnings, you should create the missing device nodes
293 swift 1.8 as described below.
294     </p>
295    
296     <p>
297     To see which devices nodes are present before the <path>/dev</path> filesystem
298     is mounted, run the following commands:
299     </p>
300    
301     <pre caption="Listing device nodes available at boot">
302     # <i>mkdir test</i>
303     # <i>mount --bind / test</i>
304     # <i>cd test/dev</i>
305     # <i>ls</i>
306     </pre>
307    
308     <p>
309 neysx 1.9 The devices needed for a successful boot are <path>/dev/null</path> and
310 swift 1.8 <path>/dev/console</path>. If they didn't show up in the previous test, you have
311 cam 1.12 to create them manually. Issue the following commands in the
312     <path>test/dev/</path> directory:
313 swift 1.1 </p>
314    
315     <pre caption="Creating necessary device node files">
316 cam 1.11 # <i>mknod -m 660 console c 5 1</i>
317     # <i>mknod -m 660 null c 1 3</i>
318 swift 1.1 </pre>
319    
320     <p>
321 swift 1.8 When you're finished, don't forget to unmount the <path>test/</path> directory:
322 swift 1.1 </p>
323    
324 swift 1.8 <pre caption="Unmounting the test/ directory">
325 cam 1.11 # <i>cd ../..</i>
326 swift 1.8 # <i>umount test</i>
327 cam 1.11 # <i>rmdir test</i>
328 swift 1.8 </pre>
329    
330     </body>
331     </section>
332     <section>
333     <title>udev and nvidia</title>
334     <body>
335    
336 swift 1.1 <p>
337 swift 1.8 If you use the proprietary driver from nVidia and the X server fails to start on
338     a udev-only system, then make sure you have:
339 swift 1.1 </p>
340    
341 swift 1.8 <ul>
342     <li>
343     the <c>nvidia</c> module listed in
344     <path>/etc/modules.autoload.d/kernel-2.6</path>
345     </li>
346     <li>
347 swift 1.10 a version of <c>nvidia-kernel</c> equal to or greater than
348 swift 1.8 <c>media-video/nvidia-kernel-1.0.5336-r2</c>
349     </li>
350     <li>
351     a version of baselayout equal to or greater than
352     <c>sys-apps/baselayout-1.8.12</c>
353     </li>
354     </ul>
355    
356 swift 1.28 <p>
357     If <c>xorg-x11</c> refuses to start, it might be because the
358     <path>/dev/nvidia</path> device file is missing. If that is the case, run
359     <path>/sbin/NVmakedevices.sh</path> to (re)create it.
360     </p>
361    
362 swift 1.1 </body>
363     </section>
364     <section>
365 swift 1.17 <title>LVM2 Names Disappear</title>
366     <body>
367    
368     <p>
369     When you use <c>udev</c> and LVM2 together, you might notice that your created
370     volume groups and logical volumes have disappeared. Well, they haven't, but they
371     are unfortunately named <path>/dev/dm-#</path> with # being 0, 1, ...
372     </p>
373    
374     <p>
375     To fix this, edit <path>/etc/udev/rules.d/50-udev.rules</path> and uncomment the
376     following line:
377     </p>
378    
379     <pre caption="Uncomment this line from /etc/udev/rules.d/50-udev.rules">
380     KERNEL="dm-[0-9]*", PROGRAM="/sbin/devmap_name %M %m", NAME="%k", SYMLINK="%c"
381     </pre>
382    
383 swift 1.27 <p>
384     Next, install <c>sys-fs/multipath-tools</c> which contains the
385     <c>devmap_name</c> application.
386     </p>
387    
388     <pre caption="Installing multipath-tools">
389     <comment>(At the moment of writing, multipath-tools is only available in the testing branch:)</comment>
390     # <i>echo "=sys-fs/multipath-tools-0.4.2 ~x86" &gt;&gt; /etc/portage/package.keywords</i>
391     # <i>emerge multipath-tools</i>
392     </pre>
393    
394 swift 1.17 </body>
395     </section>
396     <section>
397 swift 1.18 <title>No Consistent Naming between DevFS and udev</title>
398     <body>
399    
400     <p>
401     Even though our intention is to have a consistent naming scheme between both
402     dynamical device management solutions, sometimes naming differences do occur.
403 swift 1.22 </p>
404    
405     <p>
406 swift 1.18 One reported clash is with a HP Smart Array 5i RAID controller (more precisely
407     the <c>cciss</c> kernel module). With udev, the devices are named
408     <path>/dev/cciss/cXdYpZ</path> with X, Y and Z regular numbers. With devfs, the
409     devices are <path>/dev/hostX/targetY/partZ</path> or symlinked from
410     <path>/dev/cciss/cXdY</path>.
411     </p>
412    
413     <p>
414     If this is the case, don't forget to update your <path>/etc/fstab</path> and
415     bootloader configuration files accordingly.
416     </p>
417    
418 swift 1.22 <p>
419     The same happens with all-round symlinks that used to exist in
420     <path>/dev</path>, such as <path>/dev/mouse</path>, which <c>udev</c> doesn't
421     create anymore. Be certain to check your X configuration file and see if the
422 swift 1.23 Device rule for your mouse points to an existing device file.
423 swift 1.22 </p>
424    
425 fox2mike 1.29 <p>
426     Another issue is the difference in naming of terminals between devfs and udev.
427 nightmorph 1.31 While devfs calls its terminals <c>tty</c>, udev calls them <c>vc</c> and
428     <c>tty</c>. This could lead to a problem in case you are restricting root
429     logins from consoles using <path>/etc/securetty</path>. You will need to make
430     sure that both <c>tty1</c> and <c>vc/1</c> are listed in
431     <path>/etc/securetty</path> to ensure that root can login using the console.
432 fox2mike 1.29 </p>
433    
434 swift 1.18 </body>
435     </section>
436     <section>
437 swift 1.8 <title>Other issues</title>
438 swift 1.1 <body>
439    
440 swift 1.8 <p>
441     If device nodes are not created when a module is loaded from
442     <path>/etc/modules.autoload.d/kernel-2.6</path> but they appear when you load
443     the module manually with modprobe then you should try upgrading to
444     <c>sys-apps/baselayout-1.8.12</c> or later.
445     </p>
446 swift 1.7
447     <p>
448 swift 1.8 Support for the framebuffer devices (<path>/dev/fb/*</path>) comes with the
449     kernel starting from version 2.6.6-rc2.
450 swift 1.7 </p>
451    
452     <p>
453 swift 1.8 For kernels older than 2.6.4 you have to explicitly include support for the
454     <path>/dev/pts</path> filesystem.
455 swift 1.1 </p>
456    
457 swift 1.8 <pre caption="Enabling the /dev/pts filesystem">
458     File systems ---&gt;
459     Pseudo filesystems ---&gt;
460     [*] /dev/pts file system for Unix98 PTYs
461     </pre>
462    
463 swift 1.1 </body>
464     </section>
465     </chapter>
466    
467     <chapter>
468     <title>Resources &amp; Acknowledgements</title>
469     <section>
470     <body>
471    
472     <p>
473     The udev talk on the Linux Symposium (Ottawa, Ontario Canada - 2003) given by
474     Greg Kroah-Hartman (IBM Corporation) provided a solid understanding on the udev
475     application.
476     </p>
477    
478     <p>
479     <uri link="http://webpages.charter.net/decibelshelp/LinuxHelp_UDEVPrimer.html">Decibel's
480     UDEV Primer</uri> is an in-depth document about udev and Gentoo.
481     </p>
482    
483 swift 1.8 <p>
484     <uri link="http://www.reactivated.net/udevrules.php">Writing udev rules</uri> by
485     fellow Gentoo developer Daniel Drake is an excellent document to learn how to
486     customize your udev installation.
487     </p>
488    
489 swift 1.1 </body>
490     </section>
491     </chapter>
492    
493     </guide>

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