Changeset 46a2e9c for chapter07/usage.xml
- Timestamp:
- 01/06/2006 02:59:05 AM (19 years ago)
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- e1ca33a
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- 1714f1a
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chapter07/usage.xml (modified) (2 diffs)
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chapter07/usage.xml
r1714f1a r46a2e9c 1 1 <?xml version="1.0" encoding="ISO-8859-1"?> 2 <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [ 2 <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" 3 "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [ 3 4 <!ENTITY % general-entities SYSTEM "../general.ent"> 4 5 %general-entities; 5 6 ]> 7 6 8 <sect1 id="ch-scripts-usage"> 7 <title>How Do These Bootscripts Work?</title> 8 <?dbhtml filename="usage.html"?> 9 <?dbhtml filename="usage.html"?> 9 10 10 <indexterm zone="ch-scripts-usage"> 11 <primary sortas="a-Bootscripts">Bootscripts</primary> 12 <secondary>usage</secondary></indexterm> 11 <title>How Do These Bootscripts Work?</title> 13 12 14 <para>Linux uses a special booting facility named SysVinit that is based on a 15 concept of <emphasis>run-levels</emphasis>. It can be quite different from one 16 system to another, so it cannot be assumed that because things worked in one 17 particular Linux distribution, they should work the same in LFS too. LFS has its 18 own way of doing things, but it respects generally accepted standards.</para> 13 <indexterm zone="ch-scripts-usage"> 14 <primary sortas="a-Bootscripts">Bootscripts</primary> 15 <secondary>usage</secondary> 16 </indexterm> 19 17 20 <para>SysVinit (which will be referred to as <quote>init</quote> from now on) 21 works using a run-levels scheme. There are seven (numbered 0 to 6) run-levels 22 (actually, there are more run-levels, but they are for special cases and are 23 generally not used. See <filename>init(8)</filename> for more details), and each one 24 of those corresponds to the actions the computer is supposed to perform when it 25 starts up. The default run-level is 3. Here are the descriptions of the 26 different run-levels as they are implemented:</para> 18 <para>Linux uses a special booting facility named SysVinit that is based on a 19 concept of <emphasis>run-levels</emphasis>. It can be quite different from one 20 system to another, so it cannot be assumed that because things worked in one 21 particular Linux distribution, they should work the same in LFS too. LFS has its 22 own way of doing things, but it respects generally accepted standards.</para> 23 24 <para>SysVinit (which will be referred to as <quote>init</quote> from now on) 25 works using a run-levels scheme. There are seven (numbered 0 to 6) run-levels 26 (actually, there are more run-levels, but they are for special cases and are 27 generally not used. See <filename>init(8)</filename> for more details), and 28 each one of those corresponds to the actions the computer is supposed to 29 perform when it starts up. The default run-level is 3. Here are the 30 descriptions of the different run-levels as they are implemented:</para> 27 31 28 32 <literallayout>0: halt the computer … … 34 38 6: reboot the computer</literallayout> 35 39 36 <para>The command used to change run-levels is <command>init37 <replaceable>[runlevel]</replaceable></command>, where38 <replaceable>[runlevel]</replaceable> is the target run-level. For example, to39 reboot the computer, a user could issue the <command>init 6</command> command,40 which is an alias for the <command>reboot</command> command. Likewise,41 <command>init 0</command> is an alias for the <command>halt</command>42 command.</para>40 <para>The command used to change run-levels is <command>init 41 <replaceable>[runlevel]</replaceable></command>, where 42 <replaceable>[runlevel]</replaceable> is the target run-level. For example, to 43 reboot the computer, a user could issue the <command>init 6</command> command, 44 which is an alias for the <command>reboot</command> command. Likewise, 45 <command>init 0</command> is an alias for the <command>halt</command> 46 command.</para> 43 47 44 <para>There are a number of directories under <filename45 class="directory">/etc/rc.d</filename> that look like <filename46 class="directory">rc?.d</filename> (where ? is the number of the run-level) and47 <filename class="directory">rcsysinit.d</filename>, all containing a number of48 symbolic links. Some begin with a <emphasis>K</emphasis>, the others begin with49 an <emphasis>S</emphasis>, and all of them have two numbers following the50 initial letter. The K means to stop (kill) a service and the S means to start a51 service. The numbers determine the order in which the scripts are run, from 0052 to 99—the lower the number the earlier it gets executed. When53 <command>init</command> switches to another run-level, the appropriate services54 are either started or stopped, depending on the runlevel chosen.</para>48 <para>There are a number of directories under <filename 49 class="directory">/etc/rc.d</filename> that look like <filename 50 class="directory">rc?.d</filename> (where ? is the number of the run-level) and 51 <filename class="directory">rcsysinit.d</filename>, all containing a number of 52 symbolic links. Some begin with a <emphasis>K</emphasis>, the others begin with 53 an <emphasis>S</emphasis>, and all of them have two numbers following the 54 initial letter. The K means to stop (kill) a service and the S means to start a 55 service. The numbers determine the order in which the scripts are run, from 00 56 to 99—the lower the number the earlier it gets executed. When 57 <command>init</command> switches to another run-level, the appropriate services 58 are either started or stopped, depending on the runlevel chosen.</para> 55 59 56 <para>The real scripts are in <filename 57 class="directory">/etc/rc.d/init.d</filename>. They do the actual 58 work, and the symlinks all point to them. Killing links and starting 59 links point to the same script in <filename 60 class="directory">/etc/rc.d/init.d</filename>. This is because the 61 scripts can be called with different parameters like 62 <parameter>start</parameter>, <parameter>stop</parameter>, 63 <parameter>restart</parameter>, <parameter>reload</parameter>, and 64 <parameter>status</parameter>. When a K link is encountered, the 65 appropriate script is run with the <parameter>stop</parameter> 66 argument. When an S link is encountered, the appropriate script is run 67 with the <parameter>start</parameter> argument.</para> 60 <para>The real scripts are in <filename 61 class="directory">/etc/rc.d/init.d</filename>. They do the actual work, and 62 the symlinks all point to them. Killing links and starting links point to 63 the same script in <filename class="directory">/etc/rc.d/init.d</filename>. 64 This is because the scripts can be called with different parameters like 65 <parameter>start</parameter>, <parameter>stop</parameter>, 66 <parameter>restart</parameter>, <parameter>reload</parameter>, and 67 <parameter>status</parameter>. When a K link is encountered, the appropriate 68 script is run with the <parameter>stop</parameter> argument. When an S link 69 is encountered, the appropriate script is run with the 70 <parameter>start</parameter> argument.</para> 68 71 69 <para>There is one exception to this explanation. Links that start70 with an <emphasis>S</emphasis> in the <filename71 class="directory">rc0.d</filename> and <filename72 class="directory">rc6.d</filename> directories will not cause anything73 to be started. They will be called with the parameter74 <parameter>stop</parameter> to stop something. The logic behind this75 is that when a user is going to reboot or halt the system, nothing76 needs to be started. The system only needs to be stopped.</para>72 <para>There is one exception to this explanation. Links that start 73 with an <emphasis>S</emphasis> in the <filename 74 class="directory">rc0.d</filename> and <filename 75 class="directory">rc6.d</filename> directories will not cause anything 76 to be started. They will be called with the parameter 77 <parameter>stop</parameter> to stop something. The logic behind this 78 is that when a user is going to reboot or halt the system, nothing 79 needs to be started. The system only needs to be stopped.</para> 77 80 78 <para>These are descriptions of what the arguments make the scripts79 do:</para>81 <para>These are descriptions of what the arguments make the scripts 82 do:</para> 80 83 81 <variablelist> 82 <varlistentry> 83 <term><parameter>start</parameter></term> 84 <listitem><para>The service is started.</para></listitem> 85 </varlistentry> 84 <variablelist> 86 85 87 <varlistentry> 88 <term><parameter>stop</parameter></term> 89 <listitem><para>The service is stopped.</para></listitem> 90 </varlistentry> 86 <varlistentry> 87 <term><parameter>start</parameter></term> 88 <listitem> 89 <para>The service is started.</para> 90 </listitem> 91 </varlistentry> 91 92 92 <varlistentry> 93 <term><parameter>restart</parameter></term> 94 <listitem><para>The service is stopped and then started again.</para></listitem> 95 </varlistentry> 93 <varlistentry> 94 <term><parameter>stop</parameter></term> 95 <listitem> 96 <para>The service is stopped.</para> 97 </listitem> 98 </varlistentry> 96 99 97 <varlistentry>98 <term><parameter>reload</parameter></term>99 <listitem><para>The configuration of the service is updated. 100 This is used after the configuration file of a service was modified, when 101 the service does not need to be restarted.</para></listitem>102 </varlistentry>100 <varlistentry> 101 <term><parameter>restart</parameter></term> 102 <listitem> 103 <para>The service is stopped and then started again.</para> 104 </listitem> 105 </varlistentry> 103 106 104 <varlistentry> 105 <term><parameter>status</parameter></term> 106 <listitem><para>Tells if the service is running and with which PIDs.</para></listitem> 107 </varlistentry> 108 </variablelist> 107 <varlistentry> 108 <term><parameter>reload</parameter></term> 109 <listitem> 110 <para>The configuration of the service is updated. 111 This is used after the configuration file of a service was modified, when 112 the service does not need to be restarted.</para> 113 </listitem> 114 </varlistentry> 109 115 110 <para>Feel free to modify the way the boot process works (after all, 111 it is your own LFS system). The files given here are an example of how 112 it can be done.</para> 116 <varlistentry> 117 <term><parameter>status</parameter></term> 118 <listitem> 119 <para>Tells if the service is running and with which PIDs.</para> 120 </listitem> 121 </varlistentry> 122 123 </variablelist> 124 125 <para>Feel free to modify the way the boot process works (after all, 126 it is your own LFS system). The files given here are an example of how 127 it can be done.</para> 113 128 114 129 </sect1> 115
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