source: BOOK/bootscripts/common/usage.xml @ 6cc3c3f

clfs-3.0.0-systemdclfs-3.0.0-sysvinitsystemdsysvinit
Last change on this file since 6cc3c3f was 6cc3c3f, checked in by Joe Ciccone <jciccone@…>, 13 years ago

Add a note to the usage page to completly disregard it until
it can be re-written to show how systemd controls services.

  • Property mode set to 100644
File size: 5.6 KB
Line 
1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4  <!ENTITY % general-entities SYSTEM "../../general.ent">
5  %general-entities;
6]>
7
8<sect1 id="ch-scripts-usage">
9  <?dbhtml filename="usage.html"?>
10
11  <title>How Do These Bootscripts Work?</title>
12
13  <indexterm zone="ch-scripts-usage">
14    <primary sortas="a-Bootscripts">Bootscripts</primary>
15  <secondary>usage</secondary></indexterm>
16
17  <warning>
18    <para>Please completely disregard this page until it can be
19    rewritten.</para>
20  </warning>
21
22  <para>Linux uses a special booting facility named SysVinit that is
23  based on a concept of <emphasis>run-levels</emphasis>. It can be quite
24  different from one system to another, so it cannot be assumed that
25  because things worked in one particular Linux distribution, they should work
26  the same in CLFS too. CLFS has its own way of doing things, but it
27  respects generally accepted standards.</para>
28
29  <para>SysVinit (which will be referred to as <quote>init</quote> from
30  now on) works using a run-levels scheme. There are seven (numbered 0 to 6)
31  run-levels (actually, there are more run-levels, but they are for
32  special cases and are generally not used. See <filename>init(8)</filename>
33  for more details), and each one of those corresponds to the actions the
34  computer is supposed to perform when it starts up. The default
35  run-level is 3. Here are the descriptions of the different run-levels
36  as they are implemented:</para>
37
38<literallayout>0: halt the computer
391: single-user mode
402: multi-user mode without networking
413: multi-user mode with networking
424: reserved for customization, otherwise does the same as 3
435: same as 4, it is usually used for GUI login (like X's <command>xdm</command> or KDE's <command>kdm</command>)
446: reboot the computer</literallayout>
45
46  <para>The command used to change run-levels is <command>init
47  <replaceable>[runlevel]</replaceable></command>, where
48  <replaceable>[runlevel]</replaceable> is the target run-level. For example,
49  to reboot the computer, a user could issue the <command>init 6</command>
50  command, which is an alias for the <command>reboot</command> command.
51  Likewise, <command>init 0</command> is an alias for the
52  <command>halt</command> command.</para>
53
54  <para>There are a number of directories under <filename
55  class="directory">/etc/rc.d</filename> that look like <filename
56  class="directory">rc?.d</filename> (where ? is the number of the
57  run-level) and <filename class="directory">rcsysinit.d</filename>, all
58  containing a number of symbolic links. Some begin with a
59  <emphasis>K</emphasis>, the others begin with an
60  <emphasis>S</emphasis>, and all of them have two numbers following the
61  initial letter. The K means to stop (kill) a service and the S means
62  to start a service. The numbers determine the order in which the
63  scripts are run, from 00 to 99&mdash;the lower the number the earlier it
64  gets executed. When <command>init</command> switches to another run-level,
65  the appropriate services are either started or stopped, depending on the
66  runlevel chosen.</para>
67
68  <para>The real scripts are in <filename
69  class="directory">/etc/rc.d/init.d</filename>. They do the actual work,
70  and the symlinks all point to them. Killing links and starting links point
71  to the same script in <filename class="directory">/etc/rc.d/init.d</filename>.
72  This is because the scripts can be called with different parameters like
73  <option>start</option>, <option>stop</option>, <option>restart</option>,
74  <option>reload</option>, and <option>status</option>. When a K link is
75  encountered, the appropriate script is run with the <option>stop</option>
76  argument. When an S link is encountered, the appropriate script is run
77  with the <option>start</option> argument.</para>
78
79  <para>There is one exception to this explanation. Links that start
80  with an <emphasis>S</emphasis> in the <filename
81  class="directory">rc0.d</filename> and <filename
82  class="directory">rc6.d</filename> directories will not cause anything
83  to be started. They will be called with the parameter
84  <option>stop</option> to stop something. The logic behind this
85  is that when a user is going to reboot or halt the system, nothing
86  needs to be started. The system only needs to be stopped.</para>
87
88  <para>These are descriptions of what the arguments make the scripts
89  do:</para>
90
91  <variablelist>
92    <varlistentry>
93      <term><option>start</option></term>
94      <listitem>
95        <para>The service is started.</para>
96      </listitem>
97    </varlistentry>
98
99    <varlistentry>
100      <term><option>stop</option></term>
101      <listitem>
102        <para>The service is stopped.</para>
103      </listitem>
104    </varlistentry>
105
106    <varlistentry>
107      <term><option>restart</option></term>
108      <listitem>
109        <para>The service is stopped and then started again.</para>
110      </listitem>
111    </varlistentry>
112
113    <varlistentry>
114      <term><option>reload</option></term>
115      <listitem>
116        <para>The configuration of the service is updated. This is used
117        after the configuration file of a service was modified, when the
118        service does not need to be restarted.</para>
119      </listitem>
120    </varlistentry>
121
122    <varlistentry>
123      <term><option>status</option></term>
124      <listitem>
125        <para>Tells if the service is running and with which PIDs.</para>
126      </listitem>
127    </varlistentry>
128  </variablelist>
129
130  <para>Feel free to modify the way the boot process works (after all,
131  it is your own CLFS system). The files given here are an example of how
132  it can be done.</para>
133
134</sect1>
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