[519ee45] | 1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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| 2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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| 3 | "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [
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| 4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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| 5 | %general-entities;
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| 6 | ]>
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| 7 |
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| 8 | <sect1 id="ch-scripts-usage">
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| 9 | <?dbhtml filename="usage.html"?>
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| 10 |
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| 11 | <title>How Do These Bootscripts Work?</title>
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| 12 |
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| 13 | <indexterm zone="ch-scripts-usage">
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| 14 | <primary sortas="a-Bootscripts">Bootscripts</primary>
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| 15 | <secondary>usage</secondary>
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| 16 | </indexterm>
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| 17 |
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| 18 | <para>Linux uses a special booting facility named SysVinit that is based on a
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| 19 | concept of <emphasis>run-levels</emphasis>. It can be quite different from one
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| 20 | system to another, so it cannot be assumed that because things worked in one
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| 21 | particular Linux distribution, they should work the same in LFS too. LFS has its
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| 22 | own way of doing things, but it respects generally accepted standards.</para>
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| 23 |
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| 24 | <para>SysVinit (which will be referred to as <quote>init</quote> from now on)
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| 25 | works using a run-levels scheme. There are seven (numbered 0 to 6) run-levels
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| 26 | (actually, there are more run-levels, but they are for special cases and are
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| 27 | generally not used. See <filename>init(8)</filename> for more details), and
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| 28 | each one of those corresponds to the actions the computer is supposed to
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| 29 | perform when it starts up. The default run-level is 3. Here are the
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| 30 | descriptions of the different run-levels as they are implemented:</para>
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| 31 |
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| 32 | <literallayout>0: halt the computer
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| 33 | 1: single-user mode
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| 34 | 2: multi-user mode without networking
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| 35 | 3: multi-user mode with networking
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| 36 | 4: reserved for customization, otherwise does the same as 3
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| 37 | 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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| 38 | 6: reboot the computer</literallayout>
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| 39 |
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| 40 | <para>The command used to change run-levels is <command>init
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| 41 | <replaceable><runlevel></replaceable></command>, where
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| 42 | <replaceable><runlevel></replaceable> is the target run-level. For example, to
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| 43 | reboot the computer, a user could issue the <command>init 6</command> command,
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| 44 | which is an alias for the <command>reboot</command> command. Likewise,
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| 45 | <command>init 0</command> is an alias for the <command>halt</command>
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| 46 | command.</para>
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| 47 |
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| 48 | <para>There are a number of directories under <filename
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| 49 | class="directory">/etc/rc.d</filename> that look like <filename
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| 50 | class="directory">rc?.d</filename> (where ? is the number of the run-level) and
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| 51 | <filename class="directory">rcsysinit.d</filename>, all containing a number of
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| 52 | symbolic links. Some begin with a <emphasis>K</emphasis>, the others begin with
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| 53 | an <emphasis>S</emphasis>, and all of them have two numbers following the
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| 54 | initial letter. The K means to stop (kill) a service and the S means to start a
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| 55 | service. The numbers determine the order in which the scripts are run, from 00
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| 56 | to 99—the lower the number the earlier it gets executed. When
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| 57 | <command>init</command> switches to another run-level, the appropriate services
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| 58 | are either started or stopped, depending on the runlevel chosen.</para>
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| 59 |
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| 60 | <para>The real scripts are in <filename
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| 61 | class="directory">/etc/rc.d/init.d</filename>. They do the actual work, and
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| 62 | the symlinks all point to them. Killing links and starting links point to
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| 63 | the same script in <filename class="directory">/etc/rc.d/init.d</filename>.
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| 64 | This is because the scripts can be called with different parameters like
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| 65 | <parameter>start</parameter>, <parameter>stop</parameter>,
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| 66 | <parameter>restart</parameter>, <parameter>reload</parameter>, and
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| 67 | <parameter>status</parameter>. When a K link is encountered, the appropriate
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| 68 | script is run with the <parameter>stop</parameter> argument. When an S link
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| 69 | is encountered, the appropriate script is run with the
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| 70 | <parameter>start</parameter> argument.</para>
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| 71 |
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| 72 | <para>There is one exception to this explanation. Links that start
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| 73 | with an <emphasis>S</emphasis> in the <filename
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| 74 | class="directory">rc0.d</filename> and <filename
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| 75 | class="directory">rc6.d</filename> directories will not cause anything
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| 76 | to be started. They will be called with the parameter
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| 77 | <parameter>stop</parameter> to stop something. The logic behind this
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| 78 | is that when a user is going to reboot or halt the system, nothing
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| 79 | needs to be started. The system only needs to be stopped.</para>
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| 80 |
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| 81 | <para>These are descriptions of what the arguments make the scripts
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| 82 | do:</para>
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| 83 |
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| 84 | <variablelist>
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| 85 |
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| 86 | <varlistentry>
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| 87 | <term><parameter>start</parameter></term>
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| 88 | <listitem>
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| 89 | <para>The service is started.</para>
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| 90 | </listitem>
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| 91 | </varlistentry>
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| 92 |
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| 93 | <varlistentry>
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| 94 | <term><parameter>stop</parameter></term>
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| 95 | <listitem>
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| 96 | <para>The service is stopped.</para>
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| 97 | </listitem>
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| 98 | </varlistentry>
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| 99 |
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| 100 | <varlistentry>
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| 101 | <term><parameter>restart</parameter></term>
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| 102 | <listitem>
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| 103 | <para>The service is stopped and then started again.</para>
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| 104 | </listitem>
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| 105 | </varlistentry>
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| 106 |
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| 107 | <varlistentry>
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| 108 | <term><parameter>reload</parameter></term>
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| 109 | <listitem>
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| 110 | <para>The configuration of the service is updated.
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| 111 | This is used after the configuration file of a service was modified, when
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| 112 | the service does not need to be restarted.</para>
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| 113 | </listitem>
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| 114 | </varlistentry>
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| 115 |
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| 116 | <varlistentry>
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| 117 | <term><parameter>status</parameter></term>
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| 118 | <listitem>
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| 119 | <para>Tells if the service is running and with which PIDs.</para>
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| 120 | </listitem>
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| 121 | </varlistentry>
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| 122 |
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| 123 | </variablelist>
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| 124 |
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| 125 | <para>Feel free to modify the way the boot process works (after all,
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| 126 | it is your own LFS system). The files given here are an example of how
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| 127 | it can be done.</para>
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| 128 |
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| 129 | </sect1>
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