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git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@3813 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689
109 lines
5.0 KiB
XML
109 lines
5.0 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN" "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="ch-scripts-usage">
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<title>How does the booting process with these scripts work?</title>
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<?dbhtml filename="usage.html"?>
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<indexterm zone="ch-scripts-usage">
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<primary sortas="a-Bootscripts">Bootscripts</primary>
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<secondary>usage</secondary></indexterm>
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<para>Linux uses a special booting facility named SysVinit. It's based on a
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concept of <emphasis>run-levels</emphasis>. It can be widely different
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from one system to another, so it can't be assumed that because things
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worked in <insert distro name> they should work like that in LFS
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too. LFS has its own way of doing things, but it respects generally
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accepted standards.</para>
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<para>SysVinit (which we'll call <emphasis>init</emphasis> from now on) works
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using a run-levels scheme. There are 7 (from 0 to 6) run-levels
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(actually, there are more run-levels but they are for special cases and
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generally not used. The <command>init</command> man page describes those details), and each
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one of those corresponds to the things the computer is supposed to do when
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it starts up. The default run-level is 3. Here are the descriptions of the
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different run-levels as they are often implemented:</para>
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<literallayout>0: halt the computer
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1: single-user mode
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2: multi-user mode without networking
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3: multi-user mode with networking
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4: reserved for customization, otherwise does the same as 3
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5: same as 4, it is usually used for GUI login (like X's xdm or KDE's kdm)
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6: reboot the computer</literallayout>
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<para>The command used to change run-levels is <command>init
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<runlevel></command> where <runlevel> is the target run-level. For
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example, to reboot the computer, a user would issue the <userinput>init
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6</userinput> command. The <command>reboot</command> command is just an alias for
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it, as is the <command>halt</command> command an alias for <command>init
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0</command>.</para>
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<para>There are a number of directories under <filename class="directory">/etc/rc.d</filename>
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that look like like <filename class="directory">rc?.d</filename> (where ? is the
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number of the run-level) and <filename class="directory">rcsysinit.d</filename>
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all containing a number of symbolic links. Some begin with a K, the others begin
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with an S, and all of them have two numbers following the initial letter. The K
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means to stop (kill) a service, and the S means to start a service. The numbers
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determine the order in which the scripts are run, from 00 to 99; the lower the
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number the sooner it gets executed. When init switches to another run-level, the
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appropriate services get killed and others get started.</para>
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<para>The real scripts are in <filename class="directory">/etc/rc.d/init.d</filename>.
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They do all the work, and the symlinks all point to them. Killing links and starting links
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point to the same script in <filename class="directory">/etc/rc.d/init.d</filename>.
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That's because the scripts can be called with different parameters like
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<parameter>start</parameter>, <parameter>stop</parameter>,
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<parameter>restart</parameter>, <parameter>reload</parameter>,
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<parameter>status</parameter>. When a K link is encountered, the appropriate
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script is run with the <parameter>stop</parameter> argument. When an S link is
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encountered, the appropriate script is run with the <parameter>start</parameter>
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argument.</para>
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<para>There is one exception. Links that start with an S in the
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rc0.d and rc6.d directories will not cause anything to be started. They
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will be called with the parameter <parameter>stop</parameter> to stop
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something. The logic behind it is that when you are going to reboot or
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halt the system, you don't want to start anything, only stop the
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system.</para>
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<para>These are descriptions of what the arguments make the
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scripts do:</para>
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<variablelist>
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<varlistentry>
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<term><parameter>start</parameter></term>
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<listitem><para>The service is started.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>stop</parameter></term>
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<listitem><para>The service is stopped.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>restart</parameter></term>
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<listitem><para>The service is stopped and then started again.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>reload</parameter></term>
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<listitem><para>The configuration of the service is updated.
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This is used after the configuration file of a service was modified, when
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the service doesn't need to be restarted.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>status</parameter></term>
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<listitem><para>Tells if the service is running and with which PIDs.</para></listitem>
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</varlistentry>
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</variablelist>
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<para>Feel free to modify the way the boot process works (after all, it's your
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own LFS system). The files given here are just an example of how it can be
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done in a nice way (well, what we consider nice -- you may hate it).</para>
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</sect1>
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