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776f1dc3a4
Remove doc/ files when stripping in Chapter 5. Add --noclear to agetty for tty1 in inittab. git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@9636 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689
205 lines
8.2 KiB
XML
205 lines
8.2 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/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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<?dbhtml filename="usage.html"?>
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<title>How Do These Bootscripts Work?</title>
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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>
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</indexterm>
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<para>Linux uses a special booting facility named SysVinit that is based on a
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concept of <emphasis>run-levels</emphasis>. It can be quite different from one
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system to another, so it cannot be assumed that because things worked in one
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particular Linux distribution, they should work the same in LFS too. LFS has its
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own way of doing things, but it respects generally accepted standards.</para>
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<para>SysVinit (which will be referred to as <quote>init</quote> from now on)
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works using a run-levels scheme. There are seven (numbered 0 to 6) run-levels
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(actually, there are more run-levels, but they are for special cases and are
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generally not used. See <filename>init(8)</filename> for more details), and
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each one of those corresponds to the actions the computer is supposed to
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perform when it starts up. The default run-level is 3. Here are the
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descriptions of the different run-levels as they are 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 <command>xdm</command> or KDE's <command>kdm</command>)
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6: reboot the computer</literallayout>
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<sect2 id="conf-sysvinit" role="configuration">
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<title>Configuring Sysvinit</title>
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<indexterm zone="conf-sysvinit">
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<primary sortas="a-Sysvinit">Sysvinit</primary>
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<secondary>configuring</secondary>
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</indexterm>
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<indexterm zone="conf-sysvinit">
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<primary sortas="e-/etc/inittab">/etc/inittab</primary>
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</indexterm>
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<para>During the kernel initialization, the first program that is run
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is either specified on the command line or, by default
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<command>init</command>. This program reads the initialization file
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<filename>/etc/inittab</filename>. Create this file with:</para>
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<screen><userinput>cat > /etc/inittab << "EOF"
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<literal># Begin /etc/inittab
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id:3:initdefault:
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si::sysinit:/etc/rc.d/init.d/rc S
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l0:0:wait:/etc/rc.d/init.d/rc 0
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l1:S1:wait:/etc/rc.d/init.d/rc 1
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l2:2:wait:/etc/rc.d/init.d/rc 2
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l3:3:wait:/etc/rc.d/init.d/rc 3
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l4:4:wait:/etc/rc.d/init.d/rc 4
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l5:5:wait:/etc/rc.d/init.d/rc 5
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l6:6:wait:/etc/rc.d/init.d/rc 6
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ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now
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su:S016:once:/sbin/sulogin
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1:2345:respawn:/sbin/agetty --noclear tty1 9600
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2:2345:respawn:/sbin/agetty tty2 9600
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3:2345:respawn:/sbin/agetty tty3 9600
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4:2345:respawn:/sbin/agetty tty4 9600
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5:2345:respawn:/sbin/agetty tty5 9600
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6:2345:respawn:/sbin/agetty tty6 9600
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# End /etc/inittab</literal>
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EOF</userinput></screen>
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<para>An explanation of this initialization file is in the man page for
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<emphasis>inittab</emphasis>. For LFS, the key command that is run is
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<command>rc</command>. The intialization file above will instruct
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<command>rc</command> to run all the scripts starting with an S in the
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<filename class="directory">/etc/rc.d/rcsysinit.d</filename> directory
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followed by all the scripts starting with an S in the <filename
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class="directory">/etc/rc.d/rc?.d</filename> directory where the question
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mark is specified by the initdefault value.</para>
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<para>As a convenience, the <command>rc</command> script reads a library of
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functions in <filename class="directory">/lib/lsb/init-functions</filename>.
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This library also reads an optional configuration file,
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<filename>/etc/sysconfig/init_params</filename>. Any of the system
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configuration file parameters described in subsequent sections can be
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alternatively placed in this file allowing consolidation of all system
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parameters in this one file.</para>
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<para>As a debugging convenience, the functions script also logs all output
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to <filename>/run/var/bootlog</filename>. Since the <filename
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class="directory">/run</filename> directory is a tmpfs, this file is not
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persistent across boots.</para>
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</sect2>
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<sect2 id="init-levels" >
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<title>Changing Run Levels</title>
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<para>Changing run-levels is done with <command>init
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<replaceable><runlevel></replaceable></command>, where
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<replaceable><runlevel></replaceable> is the target run-level. For example, to
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reboot the computer, a user could issue the <command>init 6</command> command,
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which is an alias for the <command>reboot</command> command. Likewise,
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<command>init 0</command> is an alias for the <command>halt</command>
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command.</para>
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<para>There are a number of directories under <filename
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class="directory">/etc/rc.d</filename> that look like <filename
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class="directory">rc?.d</filename> (where ? is the number of the run-level) and
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<filename class="directory">rcsysinit.d</filename>, all containing a number of
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symbolic links. Some begin with a <emphasis>K</emphasis>, the others begin with
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an <emphasis>S</emphasis>, and all of them have two numbers following the
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initial letter. The K means to stop (kill) a service and the S means to start a
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service. The numbers determine the order in which the scripts are run, from 00
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to 99—the lower the number the earlier it gets executed. When
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<command>init</command> switches to another run-level, the appropriate services
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are either started or stopped, depending on the runlevel chosen.</para>
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<para>The real scripts are in <filename
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class="directory">/etc/rc.d/init.d</filename>. They do the actual work, and
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the symlinks all point to them. K links and S links point to
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the same script in <filename class="directory">/etc/rc.d/init.d</filename>.
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This is 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>, and
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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
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is encountered, the appropriate script is run with the
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<parameter>start</parameter> argument.</para>
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<para>There is one exception to this explanation. Links that start
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with an <emphasis>S</emphasis> in the <filename
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class="directory">rc0.d</filename> and <filename
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class="directory">rc6.d</filename> directories will not cause anything
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to be started. They will be called with the parameter
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<parameter>stop</parameter> to stop something. The logic behind this
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is that when a user is going to reboot or halt the system, nothing
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needs to be started. The system only needs to be stopped.</para>
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<para>These are descriptions of what the arguments make the scripts
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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>
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<para>The service is started.</para>
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</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>
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<para>The service is stopped.</para>
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</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>
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<para>The service is stopped and then started again.</para>
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</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>
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<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 does not need to be restarted.</para>
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</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>
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<para>Tells if the service is running and with which PIDs.</para>
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</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,
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it is your own LFS system). The files given here are an example of how
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it can be done.</para>
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</sect2>
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</sect1>
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