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https://git.linuxfromscratch.org/lfs.git
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f874424cab
Move network services to /lib/services. Move init-functions to /lib/lsb. Make /lib/lsb a symlink to /lib/services. Create convenience symlink /etc/init.d->/etc/rc.d/init.d Add help and man pages to ifup/ifdown. Append /run/var/bootlog to /var/log/boot.log at the end of the boot sequence. Add capability to step through the boot scripts at boot time. Optionally allow environment variables in sysconfig directory's console, network, and clock files to be placed in rc.site. Add an optional FASTBOOT parameter to set /fastboot when rebooting. Remove a minor warning message from udev that is triggered by the udev_retry boot script. Add SKIPTMPCLEAN as an optional parameter to skip cleaning /tmp at boot time. Add a page to Chapter 7 documenting rc.site. git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@9597 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 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 thsi 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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