1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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2 | <!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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3 | <!ENTITY % general-entities SYSTEM "../general.ent">
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4 | %general-entities;
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5 | ]>
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6 | <sect1 id="ch-scripts-usage">
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7 | <title>How does the booting process with these scripts work?</title>
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8 | <?dbhtml filename="usage.html"?>
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9 |
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10 | <indexterm zone="ch-scripts-usage">
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11 | <primary sortas="a-Bootscripts">Bootscripts</primary>
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12 | <secondary>usage</secondary></indexterm>
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13 |
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14 | <para>Linux uses a special booting facility named SysVinit. It's based on a
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15 | concept of <emphasis>run-levels</emphasis>. It can be widely different
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16 | from one system to another, so it can't be assumed that because things
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17 | worked in <insert distro name> they should work like that in LFS
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18 | too. LFS has its own way of doing things, but it respects generally
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19 | accepted standards.</para>
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20 |
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21 | <para>SysVinit (which we'll call <emphasis>init</emphasis> from now on) works
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22 | using a run-levels scheme. There are 7 (from 0 to 6) run-levels
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23 | (actually, there are more run-levels but they are for special cases and
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24 | generally not used. The <command>init</command> man page describes those details), and each
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25 | one of those corresponds to the things the computer is supposed to do when
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26 | it starts up. The default run-level is 3. Here are the descriptions of the
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27 | different run-levels as they are often implemented:</para>
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28 |
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29 | <literallayout>0: halt the computer
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30 | 1: single-user mode
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31 | 2: multi-user mode without networking
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32 | 3: multi-user mode with networking
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33 | 4: reserved for customization, otherwise does the same as 3
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34 | 5: same as 4, it is usually used for GUI login (like X's xdm or KDE's kdm)
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35 | 6: reboot the computer</literallayout>
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36 |
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37 | <para>The command used to change run-levels is <command>init
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38 | <runlevel></command> where <runlevel> is the target run-level. For
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39 | example, to reboot the computer, a user would issue the <userinput>init
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40 | 6</userinput> command. The <command>reboot</command> command is just an alias for
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41 | it, as is the <command>halt</command> command an alias for <command>init
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42 | 0</command>.</para>
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43 |
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44 | <para>There are a number of directories under <filename class="directory">/etc/rc.d</filename>
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45 | that look like like <filename class="directory">rc?.d</filename> (where ? is the
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46 | number of the run-level) and <filename class="directory">rcsysinit.d</filename>
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47 | all containing a number of symbolic links. Some begin with a K, the others begin
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48 | with an S, and all of them have two numbers following the initial letter. The K
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49 | means to stop (kill) a service, and the S means to start a service. The numbers
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50 | determine the order in which the scripts are run, from 00 to 99; the lower the
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51 | number the sooner it gets executed. When init switches to another run-level, the
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52 | appropriate services get killed and others get started.</para>
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53 |
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54 | <para>The real scripts are in <filename class="directory">/etc/rc.d/init.d</filename>.
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55 | They do all the work, and the symlinks all point to them. Killing links and starting links
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56 | point to the same script in <filename class="directory">/etc/rc.d/init.d</filename>.
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57 | That's because the scripts can be called with different parameters like
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58 | <parameter>start</parameter>, <parameter>stop</parameter>,
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59 | <parameter>restart</parameter>, <parameter>reload</parameter>,
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60 | <parameter>status</parameter>. When a K link is encountered, the appropriate
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61 | script is run with the <parameter>stop</parameter> argument. When an S link is
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62 | encountered, the appropriate script is run with the <parameter>start</parameter>
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63 | argument.</para>
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64 |
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65 | <para>There is one exception. Links that start with an S in the
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66 | rc0.d and rc6.d directories will not cause anything to be started. They
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67 | will be called with the parameter <parameter>stop</parameter> to stop
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68 | something. The logic behind it is that when you are going to reboot or
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69 | halt the system, you don't want to start anything, only stop the
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70 | system.</para>
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71 |
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72 | <para>These are descriptions of what the arguments make the
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73 | scripts do:</para>
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74 |
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75 | <variablelist>
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76 | <varlistentry>
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77 | <term><parameter>start</parameter></term>
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78 | <listitem><para>The service is started.</para></listitem>
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79 | </varlistentry>
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80 |
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81 | <varlistentry>
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82 | <term><parameter>stop</parameter></term>
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83 | <listitem><para>The service is stopped.</para></listitem>
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84 | </varlistentry>
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85 |
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86 | <varlistentry>
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87 | <term><parameter>restart</parameter></term>
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88 | <listitem><para>The service is stopped and then started again.</para></listitem>
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89 | </varlistentry>
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90 |
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91 | <varlistentry>
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92 | <term><parameter>reload</parameter></term>
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93 | <listitem><para>The configuration of the service is updated.
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94 | This is used after the configuration file of a service was modified, when
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95 | the service doesn't need to be restarted.</para></listitem>
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96 | </varlistentry>
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97 |
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98 | <varlistentry>
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99 | <term><parameter>status</parameter></term>
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100 | <listitem><para>Tells if the service is running and with which PIDs.</para></listitem>
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101 | </varlistentry>
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102 | </variablelist>
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103 |
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104 | <para>Feel free to modify the way the boot process works (after all, it's your
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105 | own LFS system). The files given here are just an example of how it can be
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106 | done in a nice way (well, what we consider nice -- you may hate it).</para>
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107 |
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108 | </sect1>
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