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>
|
---|
16 | </indexterm>
|
---|
17 |
|
---|
18 | <para>Linux uses a special booting facility named SysVinit that is based on a
|
---|
19 | concept of <emphasis>run-levels</emphasis>. It can be quite different from one
|
---|
20 | system to another, so it cannot be assumed that because things worked in one
|
---|
21 | particular Linux distribution, they should work the same in LFS too. LFS has its
|
---|
22 | own way of doing things, but it respects generally accepted standards.</para>
|
---|
23 |
|
---|
24 | <para>SysVinit (which will be referred to as <quote>init</quote> from now on)
|
---|
25 | works using a run-levels scheme. There are seven (numbered 0 to 6) run-levels
|
---|
26 | (actually, there are more run-levels, but they are for special cases and are
|
---|
27 | generally not used. See <filename>init(8)</filename> for more details), and
|
---|
28 | each one of those corresponds to the actions the computer is supposed to
|
---|
29 | perform when it starts up. The default run-level is 3. Here are the
|
---|
30 | descriptions of the different run-levels as they are implemented:</para>
|
---|
31 |
|
---|
32 | <literallayout>0: halt the computer
|
---|
33 | 1: single-user mode
|
---|
34 | 2: multi-user mode without networking
|
---|
35 | 3: multi-user mode with networking
|
---|
36 | 4: reserved for customization, otherwise does the same as 3
|
---|
37 | 5: same as 4, it is usually used for GUI login (like X's <command>xdm</command> or KDE's <command>kdm</command>)
|
---|
38 | 6: reboot the computer</literallayout>
|
---|
39 |
|
---|
40 | <sect2 id="conf-sysvinit" role="configuration">
|
---|
41 | <title>Configuring Sysvinit</title>
|
---|
42 |
|
---|
43 | <indexterm zone="conf-sysvinit">
|
---|
44 | <primary sortas="a-Sysvinit">Sysvinit</primary>
|
---|
45 | <secondary>configuring</secondary>
|
---|
46 | </indexterm>
|
---|
47 |
|
---|
48 | <indexterm zone="conf-sysvinit">
|
---|
49 | <primary sortas="e-/etc/inittab">/etc/inittab</primary>
|
---|
50 | </indexterm>
|
---|
51 |
|
---|
52 | <para>During the kernel initialization, the first program that is run
|
---|
53 | is either specified on the command line or, by default
|
---|
54 | <command>init</command>. This program reads the initialization file
|
---|
55 | <filename>/etc/inittab</filename>. Create this file with:</para>
|
---|
56 |
|
---|
57 | <screen><userinput>cat > /etc/inittab << "EOF"
|
---|
58 | <literal># Begin /etc/inittab
|
---|
59 |
|
---|
60 | id:3:initdefault:
|
---|
61 |
|
---|
62 | si::sysinit:/etc/rc.d/init.d/rc S
|
---|
63 |
|
---|
64 | l0:0:wait:/etc/rc.d/init.d/rc 0
|
---|
65 | l1:S1:wait:/etc/rc.d/init.d/rc 1
|
---|
66 | l2:2:wait:/etc/rc.d/init.d/rc 2
|
---|
67 | l3:3:wait:/etc/rc.d/init.d/rc 3
|
---|
68 | l4:4:wait:/etc/rc.d/init.d/rc 4
|
---|
69 | l5:5:wait:/etc/rc.d/init.d/rc 5
|
---|
70 | l6:6:wait:/etc/rc.d/init.d/rc 6
|
---|
71 |
|
---|
72 | ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now
|
---|
73 |
|
---|
74 | su:S016:once:/sbin/sulogin
|
---|
75 |
|
---|
76 | 1:2345:respawn:/sbin/agetty tty1 9600
|
---|
77 | 2:2345:respawn:/sbin/agetty tty2 9600
|
---|
78 | 3:2345:respawn:/sbin/agetty tty3 9600
|
---|
79 | 4:2345:respawn:/sbin/agetty tty4 9600
|
---|
80 | 5:2345:respawn:/sbin/agetty tty5 9600
|
---|
81 | 6:2345:respawn:/sbin/agetty tty6 9600
|
---|
82 |
|
---|
83 | # End /etc/inittab</literal>
|
---|
84 | EOF</userinput></screen>
|
---|
85 |
|
---|
86 | <para>An explanation of this initialization file is in the man page for
|
---|
87 | <emphasis>inittab</emphasis>. For LFS, the key command that is run is
|
---|
88 | <command>rc</command>. The intialization file above will instruct
|
---|
89 | <command>rc</command> to run all the scripts starting with an S in the
|
---|
90 | <filename class="directory">/etc/rc.d/rcsysinit.d</filename> directory
|
---|
91 | followed by all the scripts starting with an S in the <filename
|
---|
92 | class="directory">/etc/rc.d/rc?.d</filename> directory where the question
|
---|
93 | mark is specified by the initdefault value.</para>
|
---|
94 |
|
---|
95 | <para>As a convenience, the <command>rc</command> script reads a library of
|
---|
96 | functions in <filename class="directory">/lib/lsb/init-functions</filename>.
|
---|
97 | This library also reads an optional configuration file,
|
---|
98 | <filename>/etc/sysconfig/init_params</filename>. Any of the system
|
---|
99 | configuration file parameters described in subsequent sections can be
|
---|
100 | alternatively placed in this file allowing consolidation of all system
|
---|
101 | parameters in this one file.</para>
|
---|
102 |
|
---|
103 | <para>As a debugging convenience, the functions script also logs all output
|
---|
104 | to <filename>/run/var/bootlog</filename>. Since the <filename
|
---|
105 | class="directory">/run</filename> directory is a tmpfs, this file is not
|
---|
106 | persistent across boots.</para>
|
---|
107 |
|
---|
108 | </sect2>
|
---|
109 |
|
---|
110 | <sect2 id="init-levels" >
|
---|
111 | <title>Changing Run Levels</title>
|
---|
112 |
|
---|
113 | <para>Changing run-levels is done with <command>init
|
---|
114 | <replaceable><runlevel></replaceable></command>, where
|
---|
115 | <replaceable><runlevel></replaceable> is the target run-level. For example, to
|
---|
116 | reboot the computer, a user could issue the <command>init 6</command> command,
|
---|
117 | which is an alias for the <command>reboot</command> command. Likewise,
|
---|
118 | <command>init 0</command> is an alias for the <command>halt</command>
|
---|
119 | command.</para>
|
---|
120 |
|
---|
121 | <para>There are a number of directories under <filename
|
---|
122 | class="directory">/etc/rc.d</filename> that look like <filename
|
---|
123 | class="directory">rc?.d</filename> (where ? is the number of the run-level) and
|
---|
124 | <filename class="directory">rcsysinit.d</filename>, all containing a number of
|
---|
125 | symbolic links. Some begin with a <emphasis>K</emphasis>, the others begin with
|
---|
126 | an <emphasis>S</emphasis>, and all of them have two numbers following the
|
---|
127 | initial letter. The K means to stop (kill) a service and the S means to start a
|
---|
128 | service. The numbers determine the order in which the scripts are run, from 00
|
---|
129 | to 99—the lower the number the earlier it gets executed. When
|
---|
130 | <command>init</command> switches to another run-level, the appropriate services
|
---|
131 | are either started or stopped, depending on the runlevel chosen.</para>
|
---|
132 |
|
---|
133 | <para>The real scripts are in <filename
|
---|
134 | class="directory">/etc/rc.d/init.d</filename>. They do the actual work, and
|
---|
135 | the symlinks all point to them. K links and S links point to
|
---|
136 | the same script in <filename class="directory">/etc/rc.d/init.d</filename>.
|
---|
137 | This is because the scripts can be called with different parameters like
|
---|
138 | <parameter>start</parameter>, <parameter>stop</parameter>,
|
---|
139 | <parameter>restart</parameter>, <parameter>reload</parameter>, and
|
---|
140 | <parameter>status</parameter>. When a K link is encountered, the appropriate
|
---|
141 | script is run with the <parameter>stop</parameter> argument. When an S link
|
---|
142 | is encountered, the appropriate script is run with the
|
---|
143 | <parameter>start</parameter> argument.</para>
|
---|
144 |
|
---|
145 | <para>There is one exception to this explanation. Links that start
|
---|
146 | with an <emphasis>S</emphasis> in the <filename
|
---|
147 | class="directory">rc0.d</filename> and <filename
|
---|
148 | class="directory">rc6.d</filename> directories will not cause anything
|
---|
149 | to be started. They will be called with the parameter
|
---|
150 | <parameter>stop</parameter> to stop something. The logic behind this
|
---|
151 | is that when a user is going to reboot or halt the system, nothing
|
---|
152 | needs to be started. The system only needs to be stopped.</para>
|
---|
153 |
|
---|
154 | <para>These are descriptions of what the arguments make the scripts
|
---|
155 | do:</para>
|
---|
156 |
|
---|
157 | <variablelist>
|
---|
158 |
|
---|
159 | <varlistentry>
|
---|
160 | <term><parameter>start</parameter></term>
|
---|
161 | <listitem>
|
---|
162 | <para>The service is started.</para>
|
---|
163 | </listitem>
|
---|
164 | </varlistentry>
|
---|
165 |
|
---|
166 | <varlistentry>
|
---|
167 | <term><parameter>stop</parameter></term>
|
---|
168 | <listitem>
|
---|
169 | <para>The service is stopped.</para>
|
---|
170 | </listitem>
|
---|
171 | </varlistentry>
|
---|
172 |
|
---|
173 | <varlistentry>
|
---|
174 | <term><parameter>restart</parameter></term>
|
---|
175 | <listitem>
|
---|
176 | <para>The service is stopped and then started again.</para>
|
---|
177 | </listitem>
|
---|
178 | </varlistentry>
|
---|
179 |
|
---|
180 | <varlistentry>
|
---|
181 | <term><parameter>reload</parameter></term>
|
---|
182 | <listitem>
|
---|
183 | <para>The configuration of the service is updated.
|
---|
184 | This is used after the configuration file of a service was modified, when
|
---|
185 | the service does not need to be restarted.</para>
|
---|
186 | </listitem>
|
---|
187 | </varlistentry>
|
---|
188 |
|
---|
189 | <varlistentry>
|
---|
190 | <term><parameter>status</parameter></term>
|
---|
191 | <listitem>
|
---|
192 | <para>Tells if the service is running and with which PIDs.</para>
|
---|
193 | </listitem>
|
---|
194 | </varlistentry>
|
---|
195 |
|
---|
196 | </variablelist>
|
---|
197 |
|
---|
198 | <para>Feel free to modify the way the boot process works (after all,
|
---|
199 | it is your own LFS system). The files given here are an example of how
|
---|
200 | it can be done.</para>
|
---|
201 |
|
---|
202 | </sect2>
|
---|
203 |
|
---|
204 | </sect1>
|
---|