[02095ae] | 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></indexterm> |
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| 16 | |
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| 17 | <para>Linux uses a special booting facility named SysVinit that is |
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| 18 | based on a concept of <emphasis>run-levels</emphasis>. It can be quite |
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| 19 | different from one system to another, so it cannot be assumed that |
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| 20 | because things worked in one particular Linux distribution, they should work |
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[755f44a] | 21 | the same in CLFS too. CLFS has its own way of doing things, but it |
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[02095ae] | 22 | 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 |
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| 25 | now on) works using a run-levels scheme. There are seven (numbered 0 to 6) |
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| 26 | run-levels (actually, there are more run-levels, but they are for |
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| 27 | special cases and are generally not used. See <filename>init(8)</filename> |
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| 28 | for more details), and each one of those corresponds to the actions the |
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| 29 | computer is supposed to perform when it starts up. The default |
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| 30 | run-level is 3. Here are the descriptions of the different run-levels |
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| 31 | as they are implemented:</para> |
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| 32 | |
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| 33 | <literallayout>0: halt the computer |
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| 34 | 1: single-user mode |
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| 35 | 2: multi-user mode without networking |
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| 36 | 3: multi-user mode with networking |
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| 37 | 4: reserved for customization, otherwise does the same as 3 |
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| 38 | 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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| 39 | 6: reboot the computer</literallayout> |
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| 40 | |
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| 41 | <para>The command used to change run-levels is <command>init |
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| 42 | <replaceable>[runlevel]</replaceable></command>, where |
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| 43 | <replaceable>[runlevel]</replaceable> is the target run-level. For example, |
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| 44 | to reboot the computer, a user could issue the <command>init 6</command> |
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| 45 | command, which is an alias for the <command>reboot</command> command. |
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| 46 | Likewise, <command>init 0</command> is an alias for the |
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| 47 | <command>halt</command> command.</para> |
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| 48 | |
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| 49 | <para>There are a number of directories under <filename |
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| 50 | class="directory">/etc/rc.d</filename> that look like <filename |
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| 51 | class="directory">rc?.d</filename> (where ? is the number of the |
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| 52 | run-level) and <filename class="directory">rcsysinit.d</filename>, all |
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| 53 | containing a number of symbolic links. Some begin with a |
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| 54 | <emphasis>K</emphasis>, the others begin with an |
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| 55 | <emphasis>S</emphasis>, and all of them have two numbers following the |
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| 56 | initial letter. The K means to stop (kill) a service and the S means |
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| 57 | to start a service. The numbers determine the order in which the |
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| 58 | scripts are run, from 00 to 99—the lower the number the earlier it |
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| 59 | gets executed. When <command>init</command> switches to another run-level, |
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| 60 | the appropriate services are either started or stopped, depending on the |
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| 61 | runlevel chosen.</para> |
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| 62 | |
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| 63 | <para>The real scripts are in <filename |
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| 64 | class="directory">/etc/rc.d/init.d</filename>. They do the actual work, |
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| 65 | and the symlinks all point to them. Killing links and starting links point |
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| 66 | to the same script in <filename class="directory">/etc/rc.d/init.d</filename>. |
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| 67 | This is because the scripts can be called with different parameters like |
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| 68 | <option>start</option>, <option>stop</option>, <option>restart</option>, |
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| 69 | <option>reload</option>, and <option>status</option>. When a K link is |
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| 70 | encountered, the appropriate script is run with the <option>stop</option> |
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| 71 | argument. When an S link is encountered, the appropriate script is run |
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| 72 | with the <option>start</option> argument.</para> |
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| 73 | |
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| 74 | <para>There is one exception to this explanation. Links that start |
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| 75 | with an <emphasis>S</emphasis> in the <filename |
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| 76 | class="directory">rc0.d</filename> and <filename |
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| 77 | class="directory">rc6.d</filename> directories will not cause anything |
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| 78 | to be started. They will be called with the parameter |
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| 79 | <option>stop</option> to stop something. The logic behind this |
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| 80 | is that when a user is going to reboot or halt the system, nothing |
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| 81 | needs to be started. The system only needs to be stopped.</para> |
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| 82 | |
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| 83 | <para>These are descriptions of what the arguments make the scripts |
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| 84 | do:</para> |
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| 85 | |
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| 86 | <variablelist> |
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| 87 | <varlistentry> |
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| 88 | <term><option>start</option></term> |
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| 89 | <listitem> |
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| 90 | <para>The service is started.</para> |
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| 91 | </listitem> |
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| 92 | </varlistentry> |
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| 93 | |
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| 94 | <varlistentry> |
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| 95 | <term><option>stop</option></term> |
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| 96 | <listitem> |
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| 97 | <para>The service is stopped.</para> |
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| 98 | </listitem> |
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| 99 | </varlistentry> |
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| 100 | |
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| 101 | <varlistentry> |
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| 102 | <term><option>restart</option></term> |
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| 103 | <listitem> |
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| 104 | <para>The service is stopped and then started again.</para> |
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| 105 | </listitem> |
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| 106 | </varlistentry> |
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| 107 | |
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| 108 | <varlistentry> |
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| 109 | <term><option>reload</option></term> |
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| 110 | <listitem> |
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| 111 | <para>The configuration of the service is updated. This is used |
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| 112 | after the configuration file of a service was modified, when the |
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| 113 | service does not need to be restarted.</para> |
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| 114 | </listitem> |
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| 115 | </varlistentry> |
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| 116 | |
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| 117 | <varlistentry> |
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| 118 | <term><option>status</option></term> |
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| 119 | <listitem> |
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| 120 | <para>Tells if the service is running and with which PIDs.</para> |
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| 121 | </listitem> |
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| 122 | </varlistentry> |
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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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[755f44a] | 126 | it is your own CLFS system). The files given here are an example of how |
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[02095ae] | 127 | it can be done.</para> |
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| 128 | |
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| 129 | </sect1> |
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