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| 2 | <!DOCTYPE sections SYSTEM "/dtd/book.dtd"> |
2 | <!DOCTYPE sections SYSTEM "/dtd/book.dtd"> |
| 3 | |
3 | |
| 4 | <!-- The content of this document is licensed under the CC-BY-SA license --> |
4 | <!-- The content of this document is licensed under the CC-BY-SA license --> |
| 5 | <!-- See http://creativecommons.org/licenses/by-sa/2.5 --> |
5 | <!-- See http://creativecommons.org/licenses/by-sa/2.5 --> |
| 6 | |
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 $ --> |
7 | <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-rcscripts.xml,v 1.35 2011/08/17 07:57:23 swift Exp $ --> |
| 8 | |
8 | |
| 9 | <sections> |
9 | <sections> |
| 10 | |
10 | |
| 11 | <abstract> |
11 | <abstract> |
| 12 | Gentoo uses a special initscript format which, amongst other features, allows |
12 | Gentoo uses a special initscript format which, amongst other features, allows |
| 13 | dependency-driven decisions and virtual initscripts. This chapter explains all |
13 | dependency-driven decisions and virtual initscripts. This chapter explains all |
| 14 | these aspects and explains how to deal with these scripts. |
14 | these aspects and explains how to deal with these scripts. |
| 15 | </abstract> |
15 | </abstract> |
| 16 | |
16 | |
| 17 | <version>3</version> |
17 | <version>4</version> |
| 18 | <date>2011-08-12</date> |
18 | <date>2011-08-17</date> |
| 19 | |
19 | |
| 20 | <section> |
20 | <section> |
| 21 | <title>Runlevels</title> |
21 | <title>Runlevels</title> |
| 22 | <subsection> |
22 | <subsection> |
| 23 | <title>Booting your System</title> |
23 | <title>Booting your System</title> |
| … | |
… | |
| 452 | <subsection> |
452 | <subsection> |
| 453 | <title>Dependencies</title> |
453 | <title>Dependencies</title> |
| 454 | <body> |
454 | <body> |
| 455 | |
455 | |
| 456 | <p> |
456 | <p> |
| 457 | There are two dependencies you can define: <c>use</c> and <c>need</c>. As we |
457 | There are two dependency-alike settings you can define that influence the |
| 458 | have mentioned before, the <c>need</c> dependency is more strict than the |
458 | start-up or sequencing of init scripts: <c>use</c> and <c>need</c>. Next to |
| 459 | <c>use</c> dependency. Following this dependency type you enter the service |
459 | these two, there are also two order-influencing methods called <c>before</c> and |
| 460 | you depend on, or the <e>virtual</e> dependency. |
460 | <c>after</c>. These last two are no dependencies per se - they do not make the |
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461 | original init script fail if the selected one isn't scheduled to start (or fails |
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462 | to start). |
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463 | </p> |
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464 | |
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465 | <ul> |
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466 | <li> |
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467 | The <c>use</c> settings informs the init system that this script <e>uses</e> |
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468 | functionality offered by the selected script, but does not directly depend |
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469 | on it. A good example would be <c>use logger</c> or <c>use dns</c>. If those |
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470 | services are available, they will be put in good use, but if you do not have |
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471 | a logger or DNS server the services will still work. If the services exist, |
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472 | then they are started before the script that <c>use</c>'s them. |
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473 | </li> |
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474 | <li> |
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475 | The <c>need</c> setting is a hard dependency. It means that the script that |
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476 | is <c>need</c>'ing another script will not start before the other script is |
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477 | launched successfully. Also, if that other script is restarted, then this |
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478 | one will be restarted as well. |
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479 | </li> |
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480 | <li> |
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481 | When using <c>before</c>, then the given script is launched before the |
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482 | selected one <e>if</e> the selected one is part of the init level. So an |
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483 | init script <path>xdm</path> that defines <c>before alsasound</c> will start |
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484 | before the <path>alsasound</path> script, but only if <path>alsasound</path> |
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485 | is scheduled to start as well in the same init level. If |
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486 | <path>alsasound</path> is not scheduled to start too, then this particular |
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487 | setting has no effect and <path>xdm</path> will be started when the init |
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488 | system deems it most appropriate. |
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489 | </li> |
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490 | <li> |
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491 | Similarly, <c>after</c> informs the init system that the given script should |
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492 | be launched after the selected one <e>if</e> the selected one is part of the |
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493 | init level. If not, then the setting has no effect and the script will be |
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494 | launched by the init system when it deems it most appropriate. |
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495 | </li> |
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496 | </ul> |
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497 | |
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498 | <p> |
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499 | It should be clear from the above that <c>need</c> is the only "true" dependency |
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500 | setting as it affects if the script will be started or not. All the others are |
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501 | merely pointers towards the init system to clarify in which order scripts can be |
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502 | (or should be) launched. |
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503 | </p> |
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504 | |
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505 | <p> |
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506 | Now, if you look at many of Gentoo's available init scripts, you will notice |
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507 | that some have dependencies on things that are no init scripts. These "things" |
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508 | we call <e>virtuals</e>. |
| 461 | </p> |
509 | </p> |
| 462 | |
510 | |
| 463 | <p> |
511 | <p> |
| 464 | A <e>virtual</e> dependency is a dependency that a service provides, but that is |
512 | A <e>virtual</e> dependency is a dependency that a service provides, but that is |
| 465 | not provided solely by that service. Your init script can depend on a system |
513 | not provided solely by that service. Your init script can depend on a system |
| … | |
… | |
| 509 | <subsection> |
557 | <subsection> |
| 510 | <title>Controlling the Order</title> |
558 | <title>Controlling the Order</title> |
| 511 | <body> |
559 | <body> |
| 512 | |
560 | |
| 513 | <p> |
561 | <p> |
| 514 | In some cases you might not require a service, but want your service to be |
562 | As we described in the previous section, you can tell the init system what order |
| 515 | started <c>before</c> (or <c>after</c>) another service <e>if</e> it is |
563 | it should use for starting (or stopping) scripts. This ordering is handled both |
| 516 | available on the system (note the conditional - this is no dependency anymore) |
564 | through the dependency settings <c>use</c> and <c>need</c>, but also through the |
| 517 | <e>and</e> run in the same runlevel (note the conditional - only services in the |
565 | order settings <c>before</c> and <c>after</c>. As we have described these |
| 518 | same runlevel are involved). You can provide this information using the |
566 | earlier already, let's take a look at the Portmap service as an example of such |
| 519 | <c>before</c> or <c>after</c> settings. |
567 | init script. |
| 520 | </p> |
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| 521 | |
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| 522 | <p> |
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| 523 | As an example we view the settings of the Portmap service: |
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| 524 | </p> |
568 | </p> |
| 525 | |
569 | |
| 526 | <pre caption="The depend() function in the Portmap service"> |
570 | <pre caption="The depend() function in the Portmap service"> |
| 527 | depend() { |
571 | depend() { |
| 528 | need net |
572 | need net |
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