source: BOOK/bootscripts/common/usage.xml@ 124fbb6d

clfs-3.0.0-systemd clfs-3.0.0-sysvinit systemd sysvinit
Last change on this file since 124fbb6d was 957d7a0, checked in by Joe Ciccone <jciccone@…>, 14 years ago

Empty the usage page in the bootscripts section until it can be rewritten.

  • Property mode set to 100644
File size: 5.6 KB
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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 does systemd work?</title>
12
13 <indexterm zone="ch-scripts-usage">
14 <primary sortas="a-systemd-usage">systemd usage</primary>
15 <secondary>usage</secondary></indexterm>
16
17 <warning>
18 <para>Please disregard this page until it can be written.</para>
19 </warning>
20<!--
21 <para>Linux uses a special booting facility named SysVinit that is
22 based on a concept of <emphasis>run-levels</emphasis>. It can be quite
23 different from one system to another, so it cannot be assumed that
24 because things worked in one particular Linux distribution, they should work
25 the same in CLFS too. CLFS has its own way of doing things, but it
26 respects generally accepted standards.</para>
27
28 <para>SysVinit (which will be referred to as <quote>init</quote> from
29 now on) works using a run-levels scheme. There are seven (numbered 0 to 6)
30 run-levels (actually, there are more run-levels, but they are for
31 special cases and are generally not used. See <filename>init(8)</filename>
32 for more details), and each one of those corresponds to the actions the
33 computer is supposed to perform when it starts up. The default
34 run-level is 3. Here are the descriptions of the different run-levels
35 as they are implemented:</para>
36
37<literallayout>0: halt the computer
381: single-user mode
392: multi-user mode without networking
403: multi-user mode with networking
414: reserved for customization, otherwise does the same as 3
425: same as 4, it is usually used for GUI login (like X's <command>xdm</command> or KDE's <command>kdm</command>)
436: reboot the computer</literallayout>
44
45 <para>The command used to change run-levels is <command>init
46 <replaceable>[runlevel]</replaceable></command>, where
47 <replaceable>[runlevel]</replaceable> is the target run-level. For example,
48 to reboot the computer, a user could issue the <command>init 6</command>
49 command, which is an alias for the <command>reboot</command> command.
50 Likewise, <command>init 0</command> is an alias for the
51 <command>halt</command> command.</para>
52
53 <para>There are a number of directories under <filename
54 class="directory">/etc/rc.d</filename> that look like <filename
55 class="directory">rc?.d</filename> (where ? is the number of the
56 run-level) and <filename class="directory">rcsysinit.d</filename>, all
57 containing a number of symbolic links. Some begin with a
58 <emphasis>K</emphasis>, the others begin with an
59 <emphasis>S</emphasis>, and all of them have two numbers following the
60 initial letter. The K means to stop (kill) a service and the S means
61 to start a service. The numbers determine the order in which the
62 scripts are run, from 00 to 99&mdash;the lower the number the earlier it
63 gets executed. When <command>init</command> switches to another run-level,
64 the appropriate services are either started or stopped, depending on the
65 runlevel chosen.</para>
66
67 <para>The real scripts are in <filename
68 class="directory">/etc/rc.d/init.d</filename>. They do the actual work,
69 and the symlinks all point to them. Killing links and starting links point
70 to the same script in <filename class="directory">/etc/rc.d/init.d</filename>.
71 This is because the scripts can be called with different parameters like
72 <option>start</option>, <option>stop</option>, <option>restart</option>,
73 <option>reload</option>, and <option>status</option>. When a K link is
74 encountered, the appropriate script is run with the <option>stop</option>
75 argument. When an S link is encountered, the appropriate script is run
76 with the <option>start</option> argument.</para>
77
78 <para>There is one exception to this explanation. Links that start
79 with an <emphasis>S</emphasis> in the <filename
80 class="directory">rc0.d</filename> and <filename
81 class="directory">rc6.d</filename> directories will not cause anything
82 to be started. They will be called with the parameter
83 <option>stop</option> to stop something. The logic behind this
84 is that when a user is going to reboot or halt the system, nothing
85 needs to be started. The system only needs to be stopped.</para>
86
87 <para>These are descriptions of what the arguments make the scripts
88 do:</para>
89
90 <variablelist>
91 <varlistentry>
92 <term><option>start</option></term>
93 <listitem>
94 <para>The service is started.</para>
95 </listitem>
96 </varlistentry>
97
98 <varlistentry>
99 <term><option>stop</option></term>
100 <listitem>
101 <para>The service is stopped.</para>
102 </listitem>
103 </varlistentry>
104
105 <varlistentry>
106 <term><option>restart</option></term>
107 <listitem>
108 <para>The service is stopped and then started again.</para>
109 </listitem>
110 </varlistentry>
111
112 <varlistentry>
113 <term><option>reload</option></term>
114 <listitem>
115 <para>The configuration of the service is updated. This is used
116 after the configuration file of a service was modified, when the
117 service does not need to be restarted.</para>
118 </listitem>
119 </varlistentry>
120
121 <varlistentry>
122 <term><option>status</option></term>
123 <listitem>
124 <para>Tells if the service is running and with which PIDs.</para>
125 </listitem>
126 </varlistentry>
127 </variablelist>
128
129 <para>Feel free to modify the way the boot process works (after all,
130 it is your own CLFS system). The files given here are an example of how
131 it can be done.</para>
132-->
133
134</sect1>
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