[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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[e12115e] | 3 | <?dbhtml filename="usage.html" dir="chapter07"?>
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[0ad6d9a] | 4 |
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[b822811] | 5 | <para>Linux uses a special booting facility named SysVinit. It's based on a
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[0ad6d9a] | 6 | concept of <emphasis>runlevels</emphasis>. It can be widely different
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[51c0c603] | 7 | from one system to another, so it can't 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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[51c0c603] | 9 | too. LFS has its own way of doing things, but it respects generally
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[b822811] | 10 | accepted standards.</para>
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[0ad6d9a] | 11 |
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[b822811] | 12 | <para>SysVinit (which we'll call <emphasis>init</emphasis> from now on) works
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[a4d9786b] | 13 | using a runlevels scheme. There are 7 (from 0 to 6) runlevels
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| 14 | (actually, there are more runlevels but they are for special cases and
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[53b5ccf] | 15 | generally not used. The init man page describes those details), and each
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| 16 | one of those corresponds to the things the computer is supposed to do when
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[a4d9786b] | 17 | it starts up. The default runlevel is 3. Here are the descriptions of the
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[b822811] | 18 | different runlevels as they are often implemented:</para>
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[0ad6d9a] | 19 |
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[b822811] | 20 | <literallayout>0: halt the computer
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[0ad6d9a] | 21 | 1: single-user mode
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| 22 | 2: multi-user mode without networking
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| 23 | 3: multi-user mode with networking
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| 24 | 4: reserved for customization, otherwise does the same as 3
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[3ccc1df] | 25 | 5: same as 4, it is usually used for GUI login (like X's xdm or KDE's kdm)
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[b822811] | 26 | 6: reboot the computer</literallayout>
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[0ad6d9a] | 27 |
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[b822811] | 28 | <para>The command used to change runlevels is <userinput>init
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[443aab7] | 29 | <runlevel></userinput> where <runlevel> is
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[53b5ccf] | 30 | the target runlevel. For example, to reboot the computer, a user would issue
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[0ad6d9a] | 31 | the init 6 command. The reboot command is just an alias, as is the halt
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[b822811] | 32 | command an alias to init 0.</para>
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[0ad6d9a] | 33 |
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[d535079] | 34 | <para>There are a number of directories under /etc/rc.d that look like
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| 35 | like rc?.d where ? is the number of the runlevel and rcsysinit.d which
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[e4ec472] | 36 | contain a number of symbolic links. Some begin with a K, the others
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[9e18782] | 37 | begin with an S, and all of them have two numbers following the initial
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[d535079] | 38 | letter. The K means to stop (kill) a service, and the S means to start a
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| 39 | service. The numbers determine the order in which the scripts are run,
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| 40 | from 00 to 99; the lower the number the sooner it gets executed. When init
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| 41 | switches to another runlevel, the appropriate services get killed and
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| 42 | others get started.</para>
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| 43 |
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| 44 | <para>The real scripts are in /etc/rc.d/init.d. They do all the work, and the
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[fa914e5] | 45 | symlinks all point to them. Killing links and starting links point to
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[d535079] | 46 | the same script in /etc/rc.d/init.d. That's because the scripts can be
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[fa914e5] | 47 | called with different parameters like start, stop, restart, reload,
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[0ad6d9a] | 48 | status. When a K link is encountered, the appropriate script is run with
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| 49 | the stop argument. When a S link is encountered, the appropriate script
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[b822811] | 50 | is run with the start argument.</para>
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[0ad6d9a] | 51 |
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[fa914e5] | 52 | <para>There is one exception. Links that start with an S in the
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| 53 | rc0.d and rc6.d directories will not cause anything to be started. They
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[090a0cc] | 54 | will be called with the parameter <emphasis>stop</emphasis> to stop
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[fa914e5] | 55 | something. The logic behind it is that when you are going to reboot or
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| 56 | halt the system, you don't want to start anything, only stop the
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| 57 | system.</para>
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| 58 |
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[b822811] | 59 | <para>These are descriptions of what the arguments make the
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| 60 | scripts do:</para>
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[b2c0c79] | 61 |
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| 62 | <itemizedlist>
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| 63 |
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[b822811] | 64 | <listitem><para><emphasis>start</emphasis>: The service is
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| 65 | started.</para></listitem>
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[b2c0c79] | 66 |
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[b822811] | 67 | <listitem><para><emphasis>stop</emphasis>: The service is
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| 68 | stopped.</para></listitem>
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[b2c0c79] | 69 |
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[b822811] | 70 | <listitem><para><emphasis>restart</emphasis>: The service is
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| 71 | stopped and then started again.</para></listitem>
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[b2c0c79] | 72 |
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[b822811] | 73 | <listitem><para><emphasis>reload</emphasis>: The configuration
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| 74 | of the service is updated.
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[53b5ccf] | 75 | This is used after the configuration file of a service was modified, when
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[b822811] | 76 | the service doesn't need to be restarted.</para></listitem>
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[b2c0c79] | 77 |
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[b822811] | 78 | <listitem><para><emphasis>status</emphasis>: Tells if the service
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[159c2d2] | 79 | is running and with which PIDs.</para></listitem>
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[b2c0c79] | 80 |
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| 81 | </itemizedlist>
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[0ad6d9a] | 82 |
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[a2cd10f] | 83 | <para>Feel free to modify the way the boot process works (after all, it's your
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| 84 | own LFS system). The files given here are just an example of how it can be
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| 85 | done in a nice way (well, what we consider nice -- you may hate it).</para>
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[0ad6d9a] | 86 |
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| 87 | </sect1>
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| 88 |
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