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Part of bug #337140 - Improve description of use/need/before/after (or clarify it more since it was already documented)

1 <?xml version='1.0' encoding='UTF-8'?>
2 <!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3
4 <!-- The content of this document is licensed under the CC-BY-SA license -->
5 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
6
7 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-rcscripts.xml,v 1.34 2011/08/14 16:12:13 swift Exp $ -->
8
9 <sections>
10
11 <abstract>
12 Gentoo uses a special initscript format which, amongst other features, allows
13 dependency-driven decisions and virtual initscripts. This chapter explains all
14 these aspects and explains how to deal with these scripts.
15 </abstract>
16
17 <version>4</version>
18 <date>2011-08-17</date>
19
20 <section>
21 <title>Runlevels</title>
22 <subsection>
23 <title>Booting your System</title>
24 <body>
25
26 <p>
27 When you boot your system, you will notice lots of text floating by. If you pay
28 close attention, you will notice this text is the same every time you reboot
29 your system. The sequence of all these actions is called the <e>boot
30 sequence</e> and is (more or less) statically defined.
31 </p>
32
33 <p>
34 First, your boot loader will load the kernel image you have defined in the
35 boot loader configuration into memory after which it tells the CPU to run the
36 kernel. When the kernel is loaded and run, it initializes all kernel-specific
37 structures and tasks and starts the <c>init</c> process.
38 </p>
39
40 <p>
41 This process then makes sure that all filesystems (defined in
42 <path>/etc/fstab</path>) are mounted and ready to be used. Then it executes
43 several scripts located in <path>/etc/init.d</path>, which will start the
44 services you need in order to have a successfully booted system.
45 </p>
46
47 <p>
48 Finally, when all scripts are executed, <c>init</c> activates the terminals
49 (in most cases just the virtual consoles which are hidden beneath <c>Alt-F1</c>,
50 <c>Alt-F2</c>, etc.) attaching a special process called <c>agetty</c> to it.
51 This process will then make sure you are able to log on through these terminals
52 by running <c>login</c>.
53 </p>
54
55 </body>
56 </subsection>
57 <subsection>
58 <title>Init Scripts</title>
59 <body>
60
61 <p>
62 Now <c>init</c> doesn't just execute the scripts in <path>/etc/init.d</path>
63 randomly. Even more, it doesn't run all scripts in <path>/etc/init.d</path>,
64 only the scripts it is told to execute. It decides which scripts to execute by
65 looking into <path>/etc/runlevels</path>.
66 </p>
67
68 <p>
69 First, <c>init</c> runs all scripts from <path>/etc/init.d</path> that have
70 symbolic links inside <path>/etc/runlevels/boot</path>. Usually, it will
71 start the scripts in alphabetical order, but some scripts have dependency
72 information in them, telling the system that another script must be run before
73 they can be started.
74 </p>
75
76 <p>
77 When all <path>/etc/runlevels/boot</path> referenced scripts are executed,
78 <c>init</c> continues with running the scripts that have a symbolic link to them
79 in <path>/etc/runlevels/default</path>. Again, it will use the alphabetical
80 order to decide what script to run first, unless a script has dependency
81 information in it, in which case the order is changed to provide a valid
82 start-up sequence.
83 </p>
84
85 </body>
86 </subsection>
87 <subsection>
88 <title>How Init Works</title>
89 <body>
90
91 <p>
92 Of course <c>init</c> doesn't decide all that by itself. It needs a
93 configuration file that specifies what actions need to be taken. This
94 configuration file is <path>/etc/inittab</path>.
95 </p>
96
97 <p>
98 If you remember the boot sequence we have just described, you will remember
99 that <c>init</c>'s first action is to mount all filesystems. This is defined in
100 the following line from <path>/etc/inittab</path>:
101 </p>
102
103 <pre caption="The system initialisation line in /etc/inittab">
104 si::sysinit:/sbin/rc sysinit
105 </pre>
106
107 <p>
108 This line tells <c>init</c> that it must run <c>/sbin/rc sysinit</c> to
109 initialize the system. The <path>/sbin/rc</path> script takes care of the
110 initialisation, so you might say that <c>init</c> doesn't do much -- it
111 delegates the task of initialising the system to another process.
112 </p>
113
114 <p>
115 Second, <c>init</c> executed all scripts that had symbolic links in
116 <path>/etc/runlevels/boot</path>. This is defined in the following line:
117 </p>
118
119 <pre caption="The system initialisation, continued">
120 rc::bootwait:/sbin/rc boot
121 </pre>
122
123 <p>
124 Again the <c>rc</c> script performs the necessary tasks. Note that the option
125 given to <c>rc</c> (<e>boot</e>) is the same as the subdirectory of
126 <path>/etc/runlevels</path> that is used.
127 </p>
128
129 <p>
130 Now <c>init</c> checks its configuration file to see what <e>runlevel</e> it
131 should run. To decide this, it reads the following line from
132 <path>/etc/inittab</path>:
133 </p>
134
135 <pre caption="The initdefault line">
136 id:3:initdefault:
137 </pre>
138
139 <p>
140 In this case (which the majority of Gentoo users will use), the <e>runlevel</e>
141 id is 3. Using this information, <c>init</c> checks what it must run to start
142 <e>runlevel 3</e>:
143 </p>
144
145 <pre caption="The runlevel definitions">
146 l0:0:wait:/sbin/rc shutdown
147 l1:S1:wait:/sbin/rc single
148 l2:2:wait:/sbin/rc nonetwork
149 l3:3:wait:/sbin/rc default
150 l4:4:wait:/sbin/rc default
151 l5:5:wait:/sbin/rc default
152 l6:6:wait:/sbin/rc reboot
153 </pre>
154
155 <p>
156 The line that defines level 3, again, uses the <c>rc</c> script to start the
157 services (now with argument <e>default</e>). Again note that the argument of
158 <c>rc</c> is the same as the subdirectory from <path>/etc/runlevels</path>.
159 </p>
160
161 <p>
162 When <c>rc</c> has finished, <c>init</c> decides what virtual consoles it should
163 activate and what commands need to be run at each console:
164 </p>
165
166 <pre caption="The virtual consoles definition">
167 c1:12345:respawn:/sbin/agetty 38400 tty1 linux
168 c2:12345:respawn:/sbin/agetty 38400 tty2 linux
169 c3:12345:respawn:/sbin/agetty 38400 tty3 linux
170 c4:12345:respawn:/sbin/agetty 38400 tty4 linux
171 c5:12345:respawn:/sbin/agetty 38400 tty5 linux
172 c6:12345:respawn:/sbin/agetty 38400 tty6 linux
173 </pre>
174
175
176 </body>
177 </subsection>
178 <subsection>
179 <title>What is a runlevel?</title>
180 <body>
181
182 <p>
183 You have seen that <c>init</c> uses a numbering scheme to decide what
184 <e>runlevel</e> it should activate. A <e>runlevel</e> is a state in which
185 your system is running and contains a collection of scripts (runlevel scripts or
186 <e>initscripts</e>) that must be executed when you enter or leave a runlevel.
187 </p>
188
189 <p>
190 In Gentoo, there are seven runlevels defined: three internal runlevels, and four
191 user-defined runlevels. The internal runlevels are called <e>sysinit</e>,
192 <e>shutdown</e> and <e>reboot</e> and do exactly what their names imply:
193 initialize the system, powering off the system and rebooting the system.
194 </p>
195
196 <p>
197 The user-defined runlevels are those with an accompanying
198 <path>/etc/runlevels</path> subdirectory: <path>boot</path>,
199 <path>default</path>, <path>nonetwork</path> and <path>single</path>. The
200 <path>boot</path> runlevel starts all system-necessary services which all other
201 runlevels use. The remaining three runlevels differ in what services they start:
202 <path>default</path> is used for day-to-day operations, <path>nonetwork</path>
203 is used in case no network connectivity is required, and <path>single</path> is
204 used when you need to fix the system.
205 </p>
206
207 </body>
208 </subsection>
209 <subsection>
210 <title>Working with the Init Scripts</title>
211 <body>
212
213 <p>
214 The scripts that the <c>rc</c> process starts are called <e>init scripts</e>.
215 Each script in <path>/etc/init.d</path> can be executed with the arguments
216 <e>start</e>, <e>stop</e>, <e>restart</e>, <e>pause</e>, <e>zap</e>,
217 <e>status</e>, <e>ineed</e>, <e>iuse</e>, <e>needsme</e>, <e>usesme</e> or
218 <e>broken</e>.
219 </p>
220
221 <p>
222 To start, stop or restart a service (and all depending services), <c>start</c>,
223 <c>stop</c> and <c>restart</c> should be used:
224 </p>
225
226 <pre caption="Starting Postfix">
227 # <i>/etc/init.d/postfix start</i>
228 </pre>
229
230 <note>
231 Only the services that <e>need</e> the given service are stopped or restarted.
232 The other depending services (those that <e>use</e> the service but don't need
233 it) are left untouched.
234 </note>
235
236 <p>
237 If you want to stop a service, but not the services that depend on it, you can
238 use the <c>pause</c> argument:
239 </p>
240
241 <pre caption="Stopping Postfix but keep the depending services running">
242 # <i>/etc/init.d/postfix pause</i>
243 </pre>
244
245 <p>
246 If you want to see what status a service has (started, stopped, paused, ...) you
247 can use the <c>status</c> argument:
248 </p>
249
250 <pre caption="Status information for postfix">
251 # <i>/etc/init.d/postfix status</i>
252 </pre>
253
254 <p>
255 If the status information tells you that the service is running, but you know
256 that it is not, then you can reset the status information to "stopped" with the
257 <c>zap</c> argument:
258 </p>
259
260 <pre caption="Resetting status information for postfix">
261 # <i>/etc/init.d/postfix zap</i>
262 </pre>
263
264 <p>
265 To also ask what dependencies the service has, you can use <c>iuse</c> or
266 <c>ineed</c>. With <c>ineed</c> you can see the services that are really
267 necessary for the correct functioning of the service. <c>iuse</c> on the other
268 hand shows the services that can be used by the service, but are not necessary
269 for the correct functioning.
270 </p>
271
272 <pre caption="Requesting a list of all necessary services on which Postfix depends">
273 # <i>/etc/init.d/postfix ineed</i>
274 </pre>
275
276 <p>
277 Similarly, you can ask what services require the service (<c>needsme</c>) or can
278 use it (<c>usesme</c>):
279 </p>
280
281 <pre caption="Requesting a list of all services that require Postfix">
282 # <i>/etc/init.d/postfix needsme</i>
283 </pre>
284
285 <p>
286 Finally, you can ask what dependencies the service requires that are missing:
287 </p>
288
289 <pre caption="Requesting a list of missing dependencies for Postfix">
290 # <i>/etc/init.d/postfix broken</i>
291 </pre>
292
293 </body>
294 </subsection>
295 </section>
296 <section>
297 <title>Working with rc-update</title>
298 <subsection>
299 <title>What is rc-update?</title>
300 <body>
301
302 <p>
303 Gentoo's init system uses a dependency-tree to decide what service needs to be
304 started first. As this is a tedious task that we wouldn't want our users to
305 have to do manually, we have created tools that ease the administration of the
306 runlevels and init scripts.
307 </p>
308
309 <p>
310 With <c>rc-update</c> you can add and remove init scripts to a runlevel. The
311 <c>rc-update</c> tool will then automatically ask the <c>depscan.sh</c> script
312 to rebuild the dependency tree.
313 </p>
314
315 </body>
316 </subsection>
317 <subsection>
318 <title>Adding and Removing Services</title>
319 <body>
320
321 <p>
322 You have already added init scripts to the "default" runlevel during the
323 installation of Gentoo. At that time you might not have had a clue what the
324 "default" is for, but now you should. The <c>rc-update</c> script requires a
325 second argument that defines the action: <e>add</e>, <e>del</e> or <e>show</e>.
326 </p>
327
328 <p>
329 To add or remove an init script, just give <c>rc-update</c> the <c>add</c> or
330 <c>del</c> argument, followed by the init script and the runlevel. For instance:
331 </p>
332
333 <pre caption="Removing Postfix from the default runlevel">
334 # <i>rc-update del postfix default</i>
335 </pre>
336
337 <p>
338 The <c>rc-update -v show</c> command will show all the available init scripts and
339 list at which runlevels they will execute:
340 </p>
341
342 <pre caption="Receiving init script information">
343 # <i>rc-update -v show</i>
344 </pre>
345
346 <p>
347 You can also run <c>rc-update show</c> (without <c>-v</c>) to just view enabled
348 init scripts and their runlevels.
349 </p>
350
351 </body>
352 </subsection>
353 </section>
354 <section>
355 <title>Configuring Services</title>
356 <subsection>
357 <title>Why the Need for Extra Configuration?</title>
358 <body>
359
360 <p>
361 Init scripts can be quite complex. It is therefore not really desirable to
362 have the users edit the init script directly, as it would make it more
363 error-prone. It is however important to be able to configure such a service. For
364 instance, you might want to give more options to the service itself.
365 </p>
366
367 <p>
368 A second reason to have this configuration outside the init script is to be
369 able to update the init scripts without the fear that your configuration
370 changes will be undone.
371 </p>
372
373 </body>
374 </subsection>
375 <subsection>
376 <title>The /etc/conf.d Directory</title>
377 <body>
378
379 <p>
380 Gentoo provides an easy way to configure such a service: every init script that
381 can be configured has a file in <path>/etc/conf.d</path>. For instance, the
382 apache2 initscript (called <path>/etc/init.d/apache2</path>) has a
383 configuration file called <path>/etc/conf.d/apache2</path>, which can contain
384 the options you want to give to the Apache 2 server when it is started:
385 </p>
386
387 <pre caption="Variable defined in /etc/conf.d/apache2">
388 APACHE2_OPTS="-D PHP5"
389 </pre>
390
391 <p>
392 Such a configuration file contains variables and variables alone (just like
393 <path>/etc/make.conf</path>), making it very easy to configure services. It also
394 allows us to provide more information about the variables (as comments).
395 </p>
396
397 </body>
398 </subsection>
399 </section>
400 <section>
401 <title>Writing Init Scripts</title>
402 <subsection>
403 <title>Do I Have To?</title>
404 <body>
405
406 <p>
407 No, writing an init script is usually not necessary as Gentoo provides
408 ready-to-use init scripts for all provided services. However, you might have
409 installed a service without using Portage, in which case you will most likely
410 have to create an init script.
411 </p>
412
413 <p>
414 Do not use the init script provided by the service if it isn't explicitly
415 written for Gentoo: Gentoo's init scripts are not compatible with the init
416 scripts used by other distributions!
417 </p>
418
419 </body>
420 </subsection>
421 <subsection>
422 <title>Layout</title>
423 <body>
424
425 <p>
426 The basic layout of an init script is shown below.
427 </p>
428
429 <pre caption="Basic layout of an init script">
430 #!/sbin/runscript
431
432 depend() {
433 <comment>(Dependency information)</comment>
434 }
435
436 start() {
437 <comment>(Commands necessary to start the service)</comment>
438 }
439
440 stop() {
441 <comment>(Commands necessary to stop the service)</comment>
442 }
443 </pre>
444
445 <p>
446 Any init script <e>requires</e> the <c>start()</c> function to be defined. All
447 other sections are optional.
448 </p>
449
450 </body>
451 </subsection>
452 <subsection>
453 <title>Dependencies</title>
454 <body>
455
456 <p>
457 There are two dependency-alike settings you can define that influence the
458 start-up or sequencing of init scripts: <c>use</c> and <c>need</c>. Next to
459 these two, there are also two order-influencing methods called <c>before</c> and
460 <c>after</c>. These last two are no dependencies per se - they do not make the
461 original init script fail if the selected one isn't scheduled to start (or fails
462 to start).
463 </p>
464
465 <ul>
466 <li>
467 The <c>use</c> settings informs the init system that this script <e>uses</e>
468 functionality offered by the selected script, but does not directly depend
469 on it. A good example would be <c>use logger</c> or <c>use dns</c>. If those
470 services are available, they will be put in good use, but if you do not have
471 a logger or DNS server the services will still work. If the services exist,
472 then they are started before the script that <c>use</c>'s them.
473 </li>
474 <li>
475 The <c>need</c> setting is a hard dependency. It means that the script that
476 is <c>need</c>'ing another script will not start before the other script is
477 launched successfully. Also, if that other script is restarted, then this
478 one will be restarted as well.
479 </li>
480 <li>
481 When using <c>before</c>, then the given script is launched before the
482 selected one <e>if</e> the selected one is part of the init level. So an
483 init script <path>xdm</path> that defines <c>before alsasound</c> will start
484 before the <path>alsasound</path> script, but only if <path>alsasound</path>
485 is scheduled to start as well in the same init level. If
486 <path>alsasound</path> is not scheduled to start too, then this particular
487 setting has no effect and <path>xdm</path> will be started when the init
488 system deems it most appropriate.
489 </li>
490 <li>
491 Similarly, <c>after</c> informs the init system that the given script should
492 be launched after the selected one <e>if</e> the selected one is part of the
493 init level. If not, then the setting has no effect and the script will be
494 launched by the init system when it deems it most appropriate.
495 </li>
496 </ul>
497
498 <p>
499 It should be clear from the above that <c>need</c> is the only "true" dependency
500 setting as it affects if the script will be started or not. All the others are
501 merely pointers towards the init system to clarify in which order scripts can be
502 (or should be) launched.
503 </p>
504
505 <p>
506 Now, if you look at many of Gentoo's available init scripts, you will notice
507 that some have dependencies on things that are no init scripts. These "things"
508 we call <e>virtuals</e>.
509 </p>
510
511 <p>
512 A <e>virtual</e> dependency is a dependency that a service provides, but that is
513 not provided solely by that service. Your init script can depend on a system
514 logger, but there are many system loggers available (metalogd, syslog-ng,
515 sysklogd, ...). As you cannot <c>need</c> every single one of them (no sensible
516 system has all these system loggers installed and running) we made sure that
517 all these services <c>provide</c> a virtual dependency.
518 </p>
519
520 <p>
521 Let us take a look at the dependency information for the postfix service.
522 </p>
523
524 <pre caption="Dependency information for Postfix">
525 depend() {
526 need net
527 use logger dns
528 provide mta
529 }
530 </pre>
531
532 <p>
533 As you can see, the postfix service:
534 </p>
535
536 <ul>
537 <li>
538 requires the (virtual) <c>net</c> dependency (which is provided by, for
539 instance, <path>/etc/init.d/net.eth0</path>)
540 </li>
541 <li>
542 uses the (virtual) <c>logger</c> dependency (which is provided by, for
543 instance, <path>/etc/init.d/syslog-ng</path>)
544 </li>
545 <li>
546 uses the (virtual) <c>dns</c> dependency (which is provided by, for
547 instance, <path>/etc/init.d/named</path>)
548 </li>
549 <li>
550 provides the (virtual) <c>mta</c> dependency (which is common for all mail
551 servers)
552 </li>
553 </ul>
554
555 </body>
556 </subsection>
557 <subsection>
558 <title>Controlling the Order</title>
559 <body>
560
561 <p>
562 As we described in the previous section, you can tell the init system what order
563 it should use for starting (or stopping) scripts. This ordering is handled both
564 through the dependency settings <c>use</c> and <c>need</c>, but also through the
565 order settings <c>before</c> and <c>after</c>. As we have described these
566 earlier already, let's take a look at the Portmap service as an example of such
567 init script.
568 </p>
569
570 <pre caption="The depend() function in the Portmap service">
571 depend() {
572 need net
573 before inetd
574 before xinetd
575 }
576 </pre>
577
578 <p>
579 You can also use the "*" glob to catch all services in the same runlevel,
580 although this isn't advisable.
581 </p>
582
583 <pre caption="Running an init script as first script in the runlevel">
584 depend() {
585 before *
586 }
587 </pre>
588
589 <p>
590 If your service must write to local disks, it should need <c>localmount</c>. If
591 it places anything in <path>/var/run</path> such as a pidfile, then it should
592 start after <c>bootmisc</c>:
593 </p>
594
595 <pre caption="Example depend() function">
596 depend() {
597 need localmount
598 after bootmisc
599 }
600 </pre>
601
602 </body>
603 </subsection>
604 <subsection>
605 <title>Standard Functions</title>
606 <body>
607
608 <p>
609 Next to the <c>depend()</c> functionality, you also need to define the
610 <c>start()</c> function. This one contains all the commands necessary to
611 initialize your service. It is advisable to use the <c>ebegin</c> and
612 <c>eend</c> functions to inform the user about what is happening:
613 </p>
614
615 <pre caption="Example start() function">
616 start() {
617 if [ "${RC_CMD}" = "restart" ];
618 then
619 <comment># Do something in case a restart requires more than stop, start</comment>
620 fi
621
622 ebegin "Starting my_service"
623 start-stop-daemon --start --exec /path/to/my_service \
624 --pidfile /path/to/my_pidfile
625 eend $?
626 }
627 </pre>
628
629 <p>
630 Both <c>--exec</c> and <c>--pidfile</c> should be used in start and stop
631 functions. If the service does not create a pidfile, then use
632 <c>--make-pidfile</c> if possible, though you should test this to be sure.
633 Otherwise, don't use pidfiles. You can also add <c>--quiet</c> to the
634 <c>start-stop-daemon</c> options, but this is not recommended unless the
635 service is extremely verbose. Using <c>--quiet</c> may hinder debugging if the
636 service fails to start.
637 </p>
638
639 <p>
640 Another notable setting used in the above example is to check the contents of
641 the <c>RC_CMD</c> variable. Unlike the previous init script system, the newer
642 <c>openrc</c> system does not support script-specific restart functionality.
643 Instead, the script needs to check the contents of the <c>RC_CMD</c> variable
644 to see if a function (be it <c>start()</c> or <c>stop()</c>) is called as part
645 of a restart or not.
646 </p>
647
648 <note>
649 Make sure that <c>--exec</c> actually calls a service and not just a shell
650 script that launches services and exits -- that's what the init script is
651 supposed to do.
652 </note>
653
654 <p>
655 If you need more examples of the <c>start()</c> function, please read the
656 source code of the available init scripts in your <path>/etc/init.d</path>
657 directory.
658 </p>
659
660 <p>
661 Another function you can define is <c>stop()</c>. You are not obliged to define
662 this function though! Our init system is intelligent enough to fill in this
663 function by itself if you use <c>start-stop-daemon</c>.
664 </p>
665
666 <p>
667 Here is an example of a <c>stop()</c> function:
668 </p>
669
670 <pre caption="Example stop() function">
671 stop() {
672 ebegin "Stopping my_service"
673 start-stop-daemon --stop --exec /path/to/my_service \
674 --pidfile /path/to/my_pidfile
675 eend $?
676 }
677 </pre>
678
679 <p>
680 If your service runs some other script (for example, bash, python, or perl),
681 and this script later changes names (for example, <c>foo.py</c> to <c>foo</c>),
682 then you will need to add <c>--name</c> to <c>start-stop-daemon</c>. You must
683 specify the name that your script will be changed to. In this example, a
684 service starts <c>foo.py</c>, which changes names to <c>foo</c>:
685 </p>
686
687 <pre caption="A service that starts the foo script">
688 start() {
689 ebegin "Starting my_script"
690 start-stop-daemon --start --exec /path/to/my_script \
691 --pidfile /path/to/my_pidfile --name foo
692 eend $?
693 }
694 </pre>
695
696 <p>
697 <c>start-stop-daemon</c> has an excellent man page available if you need more
698 information:
699 </p>
700
701 <pre caption="Getting the man page for start-stop-daemon">
702 $ <i>man start-stop-daemon</i>
703 </pre>
704
705 <p>
706 Gentoo's init script syntax is based on the Bourne Again Shell (bash) so you are
707 free to use bash-compatible constructs inside your init script. However, you may
708 want to write your init scripts to be POSIX-compliant. Future init script
709 systems may allow symlinking <path>/bin/sh</path> to other shells besides
710 bash. Init scripts that rely on bash-only features will then break these
711 configurations.
712 </p>
713
714 </body>
715 </subsection>
716 <subsection>
717 <title>Adding Custom Options</title>
718 <body>
719
720 <p>
721 If you want your init script to support more options than the ones we have
722 already encountered, you should add the option to the <c>opts</c> variable, and
723 create a function with the same name as the option. For instance, to support an
724 option called <c>restartdelay</c>:
725 </p>
726
727 <pre caption="Supporting the restartdelay option">
728 opts="${opts} restartdelay"
729
730 restartdelay() {
731 stop
732 sleep 3 <comment># Wait 3 seconds before starting again</comment>
733 start
734 }
735 </pre>
736
737 <impo>
738 The function <c>restart()</c> cannot be overridden in openrc!
739 </impo>
740
741 </body>
742 </subsection>
743 <subsection>
744 <title>Service Configuration Variables</title>
745 <body>
746
747 <p>
748 You don't have to do anything to support a configuration file in
749 <path>/etc/conf.d</path>: if your init script is executed, the following files
750 are automatically sourced (i.e. the variables are available to use):
751 </p>
752
753 <ul>
754 <li><path>/etc/conf.d/&lt;your init script&gt;</path></li>
755 <li><path>/etc/conf.d/basic</path></li>
756 <li><path>/etc/rc.conf</path></li>
757 </ul>
758
759 <p>
760 Also, if your init script provides a virtual dependency (such as <c>net</c>),
761 the file associated with that dependency (such as <path>/etc/conf.d/net</path>)
762 will be sourced too.
763 </p>
764
765 </body>
766 </subsection>
767 </section>
768 <section>
769 <title>Changing the Runlevel Behaviour</title>
770 <subsection>
771 <title>Who might benefit from this?</title>
772 <body>
773
774 <p>
775 Many laptop users know the situation: at home you need to start <c>net.eth0</c>
776 while you don't want to start <c>net.eth0</c> while you're on the road (as
777 there is no network available). With Gentoo you can alter the runlevel behaviour
778 to your own will.
779 </p>
780
781 <p>
782 For instance you can create a second "default" runlevel which you can boot that
783 has other init scripts assigned to it. You can then select at boottime what
784 default runlevel you want to use.
785 </p>
786
787 </body>
788 </subsection>
789 <subsection>
790 <title>Using softlevel</title>
791 <body>
792
793 <p>
794 First of all, create the runlevel directory for your second "default" runlevel.
795 As an example we create the <path>offline</path> runlevel:
796 </p>
797
798 <pre caption="Creating a runlevel directory">
799 # <i>mkdir /etc/runlevels/offline</i>
800 </pre>
801
802 <p>
803 Add the necessary init scripts to the newly created runlevels. For instance, if
804 you want to have an exact copy of your current <c>default</c> runlevel but
805 without <c>net.eth0</c>:
806 </p>
807
808 <pre caption="Adding the necessary init scripts">
809 <comment>(Copy all services from default runlevel to offline runlevel)</comment>
810 # <i>cd /etc/runlevels/default</i>
811 # <i>for service in *; do rc-update add $service offline; done</i>
812 <comment>(Remove unwanted service from offline runlevel)</comment>
813 # <i>rc-update del net.eth0 offline</i>
814 <comment>(Display active services for offline runlevel)</comment>
815 # <i>rc-update show offline</i>
816 <comment>(Partial sample Output)</comment>
817 acpid | offline
818 domainname | offline
819 local | offline
820 net.eth0 |
821 </pre>
822
823 <p>
824 Even though <c>net.eth0</c> has been removed from the offline runlevel,
825 <c>udev</c> might want to attempt to start any devices it detects and launch the
826 appropriate services, a functionality that is called <e>hotplugging</e>. By
827 default, Gentoo does not enable hotplugging.
828 </p>
829
830 <p>
831 If you do want to enable hotplugging, but only for a selected set of scripts,
832 use the <c>rc_hotplug</c> variable in <path>/etc/rc.conf</path>:
833 </p>
834
835 <pre caption="Disabling device initiated services in /etc/rc.conf">
836 <comment># Allow net.wlan as well as any other service, except those matching net.*
837 # to be hotplugged</comment>
838 rc_hotplug="net.wlan !net.*"
839 </pre>
840
841 <note>
842 For more information on device initiated services, please see the comments
843 inside <path>/etc/rc.conf</path>.
844 </note>
845
846 <p>
847 Now edit your bootloader configuration and add a new entry for the
848 <c>offline</c> runlevel. For instance, in <path>/boot/grub/grub.conf</path>:
849 </p>
850
851 <pre caption="Adding an entry for the offline runlevel">
852 title Gentoo Linux Offline Usage
853 root (hd0,0)
854 kernel (hd0,0)/kernel-2.4.25 root=/dev/hda3 <i>softlevel=offline</i>
855 </pre>
856
857 <p>
858 VoilĂ , you're all set now. If you boot your system and select the newly added
859 entry at boot, the <c>offline</c> runlevel will be used instead of the
860 <c>default</c> one.
861 </p>
862
863 </body>
864 </subsection>
865 <subsection>
866 <title>Using bootlevel</title>
867 <body>
868
869 <p>
870 Using <c>bootlevel</c> is completely analogous to <c>softlevel</c>. The only
871 difference here is that you define a second "boot" runlevel instead of a second
872 "default" runlevel.
873 </p>
874
875 </body>
876 </subsection>
877 </section>
878 </sections>

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