[0ad6d9a] | 1 | <sect1 id="ch07-usage">
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| 2 | <title>How does the booting process with these scripts work?</title>
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| 3 |
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| 4 | <para>
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| 5 | Linux uses a special booting facility named SysVinit. It's based on a
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| 6 | concept of <emphasis>runlevels</emphasis>. It can be widely different
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| 7 | from one system to another, so don't assume that because things
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| 8 | worked in <insert distro name> they should work like that in LFS
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| 9 | too. LFS has it's own way of doing things, but it respects generally
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| 10 | accepted standards.
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| 11 | </para>
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| 12 |
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| 13 | <para>
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| 14 | SysVinit (which we'll call <emphasis>init</emphasis> from now on) works
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| 15 | using a runlevels scheme. There are 7 (from 0 to 6) runlevels (actually
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| 16 | there are runlevels but they are for special cases and generally not used.
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| 17 | Read the init man page for those details), and each one of those
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| 18 | corresponds to the things you want your computer to do when it starts
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| 19 | up. The default runlevel is 3. Here are the descriptions of the different
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| 20 | runlevels as they are often implemented:
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| 21 | </para>
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| 22 |
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| 23 | <literallayout>
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| 24 | 0: halt the computer
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| 25 | 1: single-user mode
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| 26 | 2: multi-user mode without networking
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| 27 | 3: multi-user mode with networking
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| 28 | 4: reserved for customization, otherwise does the same as 3
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[3ccc1df] | 29 | 5: same as 4, it is usually used for GUI login (like X's xdm or KDE's kdm)
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[0ad6d9a] | 30 | 6: reboot the computer
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| 31 | </literallayout>
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| 32 |
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| 33 | <para>
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| 34 | The command used to change runlevels is <userinput>init
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[443aab7] | 35 | <runlevel></userinput> where <runlevel> is
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[0ad6d9a] | 36 | the target runlevel. For example, to reboot the computer, you'd issue
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| 37 | the init 6 command. The reboot command is just an alias, as is the halt
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| 38 | command an alias to init 0.
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| 39 | </para>
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| 40 |
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| 41 | <para>
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| 42 | The /etc/init.d/rcS script is run at every startup of the computer,
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| 43 | before any runlevel is executed and runs the scripts listed in
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| 44 | /etc/rcS.d
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| 45 | </para>
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| 46 |
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| 47 | <para>
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| 48 | There are a number of directories under /etc that look like like rc?.d
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| 49 | where ? is the number of the runlevel and rcS.d. Take a look at one of
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| 50 | them (after you finish this chapter that is, right now there's nothing
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| 51 | there yet). There are a number of symbolic links. Some begin with an K,
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| 52 | the others begin with an S, and all of them have three numbers following
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| 53 | the initial letter. The K means to stop (kill) a service, and the S means
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| 54 | to start a service. The numbers determine the order in which the scripts
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| 55 | are run, from 000 to 999; the lower the number the sooner it gets
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| 56 | executed. When init switches to another runlevel, the appropriate
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| 57 | services get killed and others get started.
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| 58 | </para>
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| 59 |
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| 60 | <para>
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| 61 | The real scripts are in /etc/init.d. They do all the work, and the
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| 62 | symlinks all point to them. You'll note that killing links and starting
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| 63 | links point to the same script in /etc/init.d. That's because the scripts
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| 64 | can be called with different parameters like start, stop, restart, reload,
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| 65 | status. When a K link is encountered, the appropriate script is run with
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| 66 | the stop argument. When a S link is encountered, the appropriate script
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| 67 | is run with the start argument.
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| 68 | </para>
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| 69 |
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[b2c0c79] | 70 | <para>
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[0ad6d9a] | 71 | These are descriptions of what the arguments make the scripts do:
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[b2c0c79] | 72 | </para>
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| 73 |
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| 74 | <itemizedlist>
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| 75 |
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| 76 | <listitem><para>
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[0ad6d9a] | 77 | <emphasis>start</emphasis>: The service is started.
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[b2c0c79] | 78 | </para></listitem>
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| 79 |
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| 80 | <listitem><para>
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[0ad6d9a] | 81 | <emphasis>stop</emphasis>: The service is stopped.
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[b2c0c79] | 82 | </para></listitem>
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| 83 |
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| 84 | <listitem><para>
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[0ad6d9a] | 85 | <emphasis>restart</emphasis>: The service is stopped and then started again.
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[b2c0c79] | 86 | </para></listitem>
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| 87 |
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| 88 | <listitem><para>
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[0ad6d9a] | 89 | <emphasis>reload</emphasis>: The configuration of the service is updated.
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| 90 | Use this after you have modified the configuration file of a service, when
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| 91 | you don't need/want to restart the service.
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[b2c0c79] | 92 | </para></listitem>
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| 93 |
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| 94 | <listitem><para>
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[0ad6d9a] | 95 | <emphasis>status</emphasis>: Tells you if the service is running and with
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[b2c0c79] | 96 | which PID's.
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| 97 | </para></listitem>
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| 98 |
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| 99 | </itemizedlist>
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[0ad6d9a] | 100 |
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| 101 | <para>
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| 102 | Feel free to modify the way the boot process works (after all it's your
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| 103 | LFS system, not ours). The files here are just an example of how you
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| 104 | can do it in a nice way (well what we consider nice anyway. You may
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| 105 | hate it).
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| 106 | </para>
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| 107 |
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| 108 | </sect1>
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| 109 |
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