[673b0d8] | 1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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[b06ca36] | 2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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| 3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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[673b0d8] | 4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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| 5 | %general-entities;
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| 6 | ]>
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[d781ffb] | 7 |
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[35a5259] | 8 | <sect1 id="ch-scripts-introduction" revision="sysv">
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[d781ffb] | 9 | <?dbhtml filename="introduction.html"?>
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[673b0d8] | 10 |
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[d781ffb] | 11 | <title>Introduction</title>
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[81fd230] | 12 |
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[cba2d4e] | 13 | <para>Booting a Linux system involves several tasks. The process must
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| 14 | mount both virtual and real file systems, initialize devices, activate swap,
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| 15 | check file systems for integrity, mount any swap partitions or files, set
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| 16 | the system clock, bring up networking, start any daemons required by the
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| 17 | system, and accomplish any other custom tasks needed by the user. This
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| 18 | process must be organized to ensure the tasks are performed in the correct
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| 19 | order but, at the same time, be executed as fast as possible.</para>
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| 20 |
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[25332b5] | 21 | <!-- <para>In the packages that were installed in Chapter 6, there were two
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[cba2d4e] | 22 | different boot systems installed. LFS provides the ability to easily
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| 23 | select which system the user wants to use and to compare and contrast the
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| 24 | two systems by actually running each system on the local computer. The
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[b3eb525] | 25 | advantages and disadvantages of these systems is presented below.</para>-->
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[cba2d4e] | 26 |
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| 27 | <sect2 id='sysv-desc'>
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| 28 | <title>System V</title>
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| 29 |
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| 30 | <para>System V is the classic boot process that has been used in Unix and
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| 31 | Unix-like systems such as Linux since about 1983. It consists of a small
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| 32 | program, <command>init</command>, that sets up basic programs such as
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| 33 | <command>login</command> (via getty) and runs a script. This script,
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| 34 | usually named <command>rc</command>, controls the execution of a set of
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| 35 | additional scripts that perform the tasks required to initialize the
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| 36 | system.</para>
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| 37 |
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| 38 | <para>The <command>init</command> program is controlled by the
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| 39 | <filename>/etc/inittab</filename> file and is organized into run levels that
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| 40 | can be run by the user:</para>
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| 41 |
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[bf58c1e] | 42 | <literallayout>
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| 43 | 0 — halt
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| 44 | 1 — Single user mode
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| 45 | 2 — Multiuser, without networking
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| 46 | 3 — Full multiuser mode
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| 47 | 4 — User definable
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| 48 | 5 — Full multiuser mode with display manager
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| 49 | 6 — reboot
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| 50 | </literallayout>
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[cba2d4e] | 51 |
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| 52 | <para>The usual default run level is 3 or 5.</para>
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| 53 |
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| 54 | <bridgehead renderas="sect3">Advantages</bridgehead>
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| 55 |
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| 56 | <itemizedlist>
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| 57 | <listitem>
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| 58 | <para>Established, well understood system.</para>
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| 59 | </listitem>
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| 60 |
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| 61 | <listitem>
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| 62 | <para>Easy to customize.</para>
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| 63 | </listitem>
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| 64 |
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| 65 | </itemizedlist>
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| 66 |
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| 67 |
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| 68 | <bridgehead renderas="sect3">Disadvantages</bridgehead>
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| 69 |
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| 70 | <itemizedlist>
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| 71 | <listitem>
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| 72 | <para>Slower to boot. A medium speed base LFS system
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| 73 | takes 8-12 seconds where the boot time is measured from the
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| 74 | first kernel message to the login prompt. Network
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| 75 | connectivity is typically established about 2 seconds
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| 76 | after the login prompt.</para>
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| 77 | </listitem>
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| 78 |
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| 79 | <listitem>
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| 80 | <para>Serial processing of boot tasks. This is related to the previous
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| 81 | point. A delay in any process such as a file system check, will
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| 82 | delay the entire boot process.</para>
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| 83 | </listitem>
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| 84 |
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| 85 | <listitem>
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| 86 | <para>Does not directly support advanced features like
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| 87 | control groups (cgroups), and per-user fair share scheduling.</para>
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| 88 | </listitem>
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| 89 |
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| 90 | <listitem>
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| 91 | <para>Adding scripts requires manual, static sequencing decisions.</para>
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| 92 | </listitem>
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| 93 |
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| 94 | </itemizedlist>
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| 95 |
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| 96 | </sect2>
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[b3eb525] | 97 | <!--
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[cba2d4e] | 98 | <sect2 id='sysd-desc'>
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| 99 | <title>Systemd</title>
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| 100 |
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| 101 | <para>Systemd is a group of interconnected programs that handles system and
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| 102 | individual process requests. It provides a dependency system between
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| 103 | various entities called "units". It automatically addresses dependencies
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| 104 | between units and can execute several startup tasks in parallel. It
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| 105 | provides login, inetd, logging, time, and networking services. </para>
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| 106 |
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| 107 | <bridgehead renderas="sect3">Advantages</bridgehead>
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| 108 |
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| 109 | <itemizedlist>
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| 110 | <listitem>
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| 111 | <para>Used on many established distributions by default.</para>
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| 112 | </listitem>
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| 113 |
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| 114 | <listitem>
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| 115 | <para>There is extensive documentation.
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| 116 | See <ulink url="http://www.freedesktop.org/wiki/Software/systemd/"/>.</para>
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| 117 | </listitem>
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[673b0d8] | 118 |
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[cba2d4e] | 119 | <listitem>
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| 120 | <para>Parallel execution of boot processes. A medium speed
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| 121 | base LFS system takes 6-10 seconds from kernel start to a
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| 122 | login prompt. Network connectivity is typically established
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| 123 | about 2 seconds after the login prompt. More complex startup
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| 124 | procedures may show a greater speedup when compared to System V.</para>
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| 125 | </listitem>
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| 126 |
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| 127 | <listitem>
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| 128 | <para>Implements advanced features such as control groups to
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| 129 | manage related processes.</para>
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| 130 | </listitem>
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| 131 |
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| 132 | <listitem>
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| 133 | <para>Maintains backward compatibility with System V programs
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| 134 | and scripts.</para>
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| 135 | </listitem>
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| 136 | </itemizedlist>
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| 137 |
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| 138 | <bridgehead renderas="sect3">Disadvantages</bridgehead>
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| 139 |
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| 140 | <itemizedlist>
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| 141 | <listitem>
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| 142 | <para>There is a substantial learning curve.</para>
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| 143 | </listitem>
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| 144 |
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| 145 | <listitem>
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| 146 | <para>Some advanced features such as dbus or cgroups cannot be
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| 147 | disabled if they are not otherwise needed.</para>
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| 148 | </listitem>
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| 149 |
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| 150 | <listitem>
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| 151 | <para>Although implemented as several executable programs
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| 152 | the user cannot choose to implement only the portions desired.</para>
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| 153 | </listitem>
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| 154 |
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| 155 | <listitem>
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| 156 | <para>Due to the nature of using compiled programs, systemd is
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| 157 | more difficult to debug.</para>
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| 158 | </listitem>
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| 159 |
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| 160 | <listitem>
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| 161 | <para>Logging is done in a binary format. Extra tools must
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| 162 | be used to process logs or additional processes must be implemented
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| 163 | to duplicate traditional logging programs.</para>
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| 164 | </listitem>
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| 165 |
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| 166 | </itemizedlist>
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| 167 |
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| 168 | </sect2>
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[b3eb525] | 169 | -->
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| 170 | <!--
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[cba2d4e] | 171 | <sect2 id='sysv'>
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| 172 | <title>Selecting a Boot Method</title>
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| 173 |
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| 174 | <para>Selecting a boot method in LFS is relatively easy.
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| 175 | Both systems are installed side-by-side. The only task needed is to
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| 176 | ensure the files that are needed by the system have the correct names.
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| 177 | The following scripts do that.</para>
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| 178 |
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[9ab3742] | 179 | <screen><userinput remap="install">cat > /usr/sbin/set-systemd << "EOF"
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[cba2d4e] | 180 | #! /bin/bash
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| 181 |
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| 182 | ln -svfn init-systemd /sbin/init
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| 183 | ln -svfn init.d-systemd /etc/init.d
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| 184 |
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| 185 | for tool in halt poweroff reboot runlevel shutdown telinit; do
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[9839808] | 186 | ln -sfvn ${tool}-systemd /sbin/${tool}
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[cba2d4e] | 187 | ln -svfn ${tool}-systemd.8 /usr/share/man/man8/${tool}.8
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| 188 | done
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| 189 |
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| 190 | echo "Now reboot with /sbin/reboot-sysv"
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| 191 | EOF
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| 192 |
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[9ab3742] | 193 | chmod 0744 /usr/sbin/set-systemd
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| 194 |
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| 195 | cat > /usr/sbin/set-sysv << "EOF"
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| 196 | #! /bin/bash
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[cba2d4e] | 197 |
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| 198 | ln -sfvn init-sysv /sbin/init
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| 199 | ln -svfn init.d-sysv /etc/init.d
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| 200 |
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| 201 | for tool in halt poweroff reboot runlevel shutdown telinit; do
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| 202 | ln -sfvn ${tool}-sysv /sbin/${tool}
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| 203 | ln -svfn ${tool}-sysv.8 /usr/share/man/man8/${tool}.8
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| 204 | done
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| 205 |
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| 206 | echo "Now reboot with /sbin/reboot-systemd"
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| 207 | EOF
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| 208 |
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[9ab3742] | 209 | chmod 0744 /usr/sbin/set-sysv</userinput></screen>
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[cba2d4e] | 210 |
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[bf58c1e] | 211 | <note><para>The comment about the correct command to reboot in the
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| 212 | above scripts is correct. The reboot command for the current boot
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| 213 | system must be used after the script changes the default reboot command.
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| 214 | </para></note>
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| 215 |
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[cba2d4e] | 216 | <para>Now set the desired boot system. The default is System V:</para>
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| 217 |
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[9ab3742] | 218 | <screen><userinput remap="install">/usr/sbin/set-sysv</userinput></screen>
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[cba2d4e] | 219 |
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| 220 | <para>Changing the boot system can be done at any time by running the
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| 221 | appropriate script above and rebooting.</para>
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| 222 |
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| 223 | </sect2>
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[b3eb525] | 224 | -->
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[d781ffb] | 225 | </sect1>
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