source: BOOK/bootscripts/common/usage.xml@ 13e20ae

clfs-1.2 clfs-2.1 clfs-3.0.0-systemd clfs-3.0.0-sysvinit systemd sysvinit
Last change on this file since 13e20ae was aa18ac0, checked in by Manuel Canales Esparcia <manuel@…>, 18 years ago

Updated trunk book sources to use DocBook-XML DTD 4.5.

  • Property mode set to 100644
File size: 5.5 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 <para>Linux uses a special booting facility named SysVinit that is
18 based on a concept of <emphasis>run-levels</emphasis>. It can be quite
19 different from one system to another, so it cannot be assumed that
20 because things worked in one particular Linux distribution, they should work
21 the same in CLFS too. CLFS has its own way of doing things, but it
22 respects generally accepted standards.</para>
23
24 <para>SysVinit (which will be referred to as <quote>init</quote> from
25 now on) works using a run-levels scheme. There are seven (numbered 0 to 6)
26 run-levels (actually, there are more run-levels, but they are for
27 special cases and are generally not used. See <filename>init(8)</filename>
28 for more details), and each one of those corresponds to the actions the
29 computer is supposed to perform when it starts up. The default
30 run-level is 3. Here are the descriptions of the different run-levels
31 as they are implemented:</para>
32
33<literallayout>0: halt the computer
341: single-user mode
352: multi-user mode without networking
363: multi-user mode with networking
374: reserved for customization, otherwise does the same as 3
385: same as 4, it is usually used for GUI login (like X's <command>xdm</command> or KDE's <command>kdm</command>)
396: reboot the computer</literallayout>
40
41 <para>The command used to change run-levels is <command>init
42 <replaceable>[runlevel]</replaceable></command>, where
43 <replaceable>[runlevel]</replaceable> is the target run-level. For example,
44 to reboot the computer, a user could issue the <command>init 6</command>
45 command, which is an alias for the <command>reboot</command> command.
46 Likewise, <command>init 0</command> is an alias for the
47 <command>halt</command> command.</para>
48
49 <para>There are a number of directories under <filename
50 class="directory">/etc/rc.d</filename> that look like <filename
51 class="directory">rc?.d</filename> (where ? is the number of the
52 run-level) and <filename class="directory">rcsysinit.d</filename>, all
53 containing a number of symbolic links. Some begin with a
54 <emphasis>K</emphasis>, the others begin with an
55 <emphasis>S</emphasis>, and all of them have two numbers following the
56 initial letter. The K means to stop (kill) a service and the S means
57 to start a service. The numbers determine the order in which the
58 scripts are run, from 00 to 99&mdash;the lower the number the earlier it
59 gets executed. When <command>init</command> switches to another run-level,
60 the appropriate services are either started or stopped, depending on the
61 runlevel chosen.</para>
62
63 <para>The real scripts are in <filename
64 class="directory">/etc/rc.d/init.d</filename>. They do the actual work,
65 and the symlinks all point to them. Killing links and starting links point
66 to the same script in <filename class="directory">/etc/rc.d/init.d</filename>.
67 This is because the scripts can be called with different parameters like
68 <option>start</option>, <option>stop</option>, <option>restart</option>,
69 <option>reload</option>, and <option>status</option>. When a K link is
70 encountered, the appropriate script is run with the <option>stop</option>
71 argument. When an S link is encountered, the appropriate script is run
72 with the <option>start</option> argument.</para>
73
74 <para>There is one exception to this explanation. Links that start
75 with an <emphasis>S</emphasis> in the <filename
76 class="directory">rc0.d</filename> and <filename
77 class="directory">rc6.d</filename> directories will not cause anything
78 to be started. They will be called with the parameter
79 <option>stop</option> to stop something. The logic behind this
80 is that when a user is going to reboot or halt the system, nothing
81 needs to be started. The system only needs to be stopped.</para>
82
83 <para>These are descriptions of what the arguments make the scripts
84 do:</para>
85
86 <variablelist>
87 <varlistentry>
88 <term><option>start</option></term>
89 <listitem>
90 <para>The service is started.</para>
91 </listitem>
92 </varlistentry>
93
94 <varlistentry>
95 <term><option>stop</option></term>
96 <listitem>
97 <para>The service is stopped.</para>
98 </listitem>
99 </varlistentry>
100
101 <varlistentry>
102 <term><option>restart</option></term>
103 <listitem>
104 <para>The service is stopped and then started again.</para>
105 </listitem>
106 </varlistentry>
107
108 <varlistentry>
109 <term><option>reload</option></term>
110 <listitem>
111 <para>The configuration of the service is updated. This is used
112 after the configuration file of a service was modified, when the
113 service does not need to be restarted.</para>
114 </listitem>
115 </varlistentry>
116
117 <varlistentry>
118 <term><option>status</option></term>
119 <listitem>
120 <para>Tells if the service is running and with which PIDs.</para>
121 </listitem>
122 </varlistentry>
123 </variablelist>
124
125 <para>Feel free to modify the way the boot process works (after all,
126 it is your own CLFS system). The files given here are an example of how
127 it can be done.</para>
128
129</sect1>
Note: See TracBrowser for help on using the repository browser.