[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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[53b5ccf] | 7 | from one system to another, so it can not be assumed that because things
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[0ad6d9a] | 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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[a4d9786b] | 15 | using a runlevels scheme. There are 7 (from 0 to 6) runlevels
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| 16 | (actually, there are more runlevels but they are for special cases and
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[53b5ccf] | 17 | generally not used. The init man page describes those details), and each
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| 18 | one of those corresponds to the things the computer is supposed to do when
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[a4d9786b] | 19 | it starts up. The default runlevel is 3. Here are the descriptions of the
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| 20 | different runlevels as they are often implemented:
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[0ad6d9a] | 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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[53b5ccf] | 36 | the target runlevel. For example, to reboot the computer, a user would issue
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[0ad6d9a] | 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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[53b5ccf] | 49 | where ? is the number of the runlevel and rcS.d. A user might take a look
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| 50 | at one of
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| 51 | them (after this chapter is finished, right now there's nothing
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[0ad6d9a] | 52 | there yet). There are a number of symbolic links. Some begin with an K,
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| 53 | the others begin with an S, and all of them have three numbers following
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| 54 | the initial letter. The K means to stop (kill) a service, and the S means
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| 55 | to start a service. The numbers determine the order in which the scripts
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| 56 | are run, from 000 to 999; the lower the number the sooner it gets
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| 57 | executed. When init switches to another runlevel, the appropriate
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| 58 | services get killed and others get started.
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| 59 | </para>
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| 60 |
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| 61 | <para>
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| 62 | The real scripts are in /etc/init.d. They do all the work, and the
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[9aab9f5] | 63 | symlinks all point to them. Killing links and starting
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[0ad6d9a] | 64 | links point to the same script in /etc/init.d. That's because the scripts
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| 65 | can be called with different parameters like start, stop, restart, reload,
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| 66 | status. When a K link is encountered, the appropriate script is run with
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| 67 | the stop argument. When a S link is encountered, the appropriate script
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| 68 | is run with the start argument.
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| 69 | </para>
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| 70 |
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[b2c0c79] | 71 | <para>
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[0ad6d9a] | 72 | These are descriptions of what the arguments make the scripts do:
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[b2c0c79] | 73 | </para>
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| 74 |
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| 75 | <itemizedlist>
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| 76 |
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| 77 | <listitem><para>
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[0ad6d9a] | 78 | <emphasis>start</emphasis>: The service is started.
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[b2c0c79] | 79 | </para></listitem>
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| 80 |
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| 81 | <listitem><para>
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[0ad6d9a] | 82 | <emphasis>stop</emphasis>: The service is stopped.
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[b2c0c79] | 83 | </para></listitem>
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| 84 |
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| 85 | <listitem><para>
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[0ad6d9a] | 86 | <emphasis>restart</emphasis>: The service is stopped and then started again.
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[b2c0c79] | 87 | </para></listitem>
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| 88 |
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| 89 | <listitem><para>
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[0ad6d9a] | 90 | <emphasis>reload</emphasis>: The configuration of the service is updated.
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[53b5ccf] | 91 | This is used after the configuration file of a service was modified, when
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| 92 | the service doesn't need to be restarted.
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[b2c0c79] | 93 | </para></listitem>
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| 94 |
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| 95 | <listitem><para>
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[53b5ccf] | 96 | <emphasis>status</emphasis>: Tells if the service is running and with
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[b2c0c79] | 97 | which PID's.
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| 98 | </para></listitem>
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| 99 |
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| 100 | </itemizedlist>
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[0ad6d9a] | 101 |
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| 102 | <para>
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[53b5ccf] | 103 | Feel free to modify the way the boot process works (after all it's the users
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| 104 | LFS system, not ours). The files here are just an example of how it can be
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| 105 | done
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| 106 | in a nice way (well what we consider nice anyway. A user may hate it).
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[0ad6d9a] | 107 | </para>
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| 108 |
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| 109 | </sect1>
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| 110 |
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