Ignore:
Timestamp:
03/31/2021 10:41:39 AM (3 years ago)
Author:
Xℹ Ruoyao <xry111@…>
Branches:
ml-11.0, multilib
Children:
7610848
Parents:
811b5a39
git-author:
Thomas Trepl <thomas@…> (06/29/2020 07:55:01 AM)
git-committer:
Xℹ Ruoyao <xry111@…> (03/31/2021 10:41:39 AM)
Message:

Update to new lfs structure

git-svn-id: ​http://svn.linuxfromscratch.org/LFS/branches/multilib@11986 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

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1 edited

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  • chapter07/introduction.xml

    r811b5a39 r6dfcfecc  
    66]>
    77
    8 <sect1 id="ch-config-introduction" revision="sysv">
     8<sect1 id="ch-tools-introduction-chroot">
    99  <?dbhtml filename="introduction.html"?>
    1010
    1111  <title>Introduction</title>
    1212
    13     <para>Booting a Linux system involves several tasks.  The process must
    14     mount both virtual and real file systems, initialize devices, activate swap,
    15     check file systems for integrity, mount any swap partitions or files, set
    16     the system clock, bring up networking, start any daemons required by the
    17     system, and accomplish any other custom tasks needed by the user.  This
    18     process must be organized to ensure the tasks are performed in the correct
    19     order but, at the same time, be executed as fast as possible.</para>
     13  <para>This chapter shows how to build the last missing bits of the temporary
     14  system: first, the tools needed by the build machinery of various packages,
     15  then three packages needed to run tests.  Now that all circular dependencies
     16  have been resolved, we can use a <quote>chroot</quote> environment,
     17  completely isolated the host operating system used for the build, except
     18  for the running kernel.</para>
    2019
    21 <!--    <para>In the packages that were installed in Chapter&nbsp;6, there were two
    22     different boot systems installed.  LFS provides the ability to easily
    23     select which system the user wants to use and to compare and contrast the
    24     two systems by actually running each system on the local computer.  The
    25     advantages and disadvantages of these systems is presented below.</para>-->
     20  <para>For proper operation of the isolated environment, some communication
     21  with the running kernel must be established. This is done through the
     22  so-called <emphasis>Virtual Kernel File Systems</emphasis>, which must be
     23  mounted when entering the chroot environment. You may want to check
     24  that they are mounted by issuing <command>findmnt</command>.</para>
    2625
    27   <sect2 id='sysv-desc'>
    28     <title>System V</title>
     26  <para>Until <xref linkend="ch-tools-chroot"/>, the commands must be
     27  run as <systemitem class="username">root</systemitem>, with the
     28  <envar>LFS</envar> variable set. After entering chroot, all commands
     29  are run as root, fortunately without access to the OS of the computer
     30  you built LFS on. Be careful anyway, as it is easy to destroy the whole
     31  LFS system with badly formed commands.</para>
    2932
    30     <para>System V is the classic boot process that has been used in Unix and
    31     Unix-like systems such as Linux since about 1983.  It consists of a small
    32     program, <command>init</command>, that sets up basic programs such as
    33     <command>login</command> (via getty) and runs a script.  This script,
    34     usually named <command>rc</command>,  controls the execution of a set of
    35     additional scripts that perform the tasks required to initialize the
    36     system.</para>
    37 
    38     <para>The <command>init</command> program is controlled by the
    39     <filename>/etc/inittab</filename> file and is organized into run levels that
    40     can be run by the user:</para>
    41 
    42 <literallayout>
    43 0 &mdash; halt
    44 1 &mdash; Single user mode
    45 2 &mdash; Multiuser, without networking
    46 3 &mdash; Full multiuser mode
    47 4 &mdash; User definable
    48 5 &mdash; Full multiuser mode with display manager
    49 6 &mdash; reboot
    50 </literallayout>
    51 
    52     <para>The usual default run level is 3 or 5.</para>
    53 
    54     <bridgehead renderas="sect3">Advantages</bridgehead>
    55 
    56     <itemizedlist>
    57       <listitem>
    58           <para>Established, well understood system.</para>
    59       </listitem>
    60 
    61       <listitem>
    62           <para>Easy to customize.</para>
    63       </listitem>
    64 
    65     </itemizedlist>
    66 
    67 
    68     <bridgehead renderas="sect3">Disadvantages</bridgehead>
    69 
    70     <itemizedlist>
    71       <listitem>
    72           <para>Slower to boot.  A medium speed base LFS system
    73           takes 8-12 seconds where the boot time is measured from the
    74           first kernel message to the login prompt.  Network
    75           connectivity is typically established about 2 seconds
    76           after the login prompt.</para>
    77       </listitem>
    78 
    79       <listitem>
    80           <para>Serial processing of boot tasks. This is related to the previous
    81           point.  A delay in any process such as a file system check, will
    82           delay the entire boot process.</para>
    83       </listitem>
    84 
    85       <listitem>
    86           <para>Does not directly support advanced features like
    87           control groups (cgroups), and per-user fair share scheduling.</para>
    88       </listitem>
    89 
    90       <listitem>
    91           <para>Adding scripts requires manual, static sequencing decisions.</para>
    92       </listitem>
    93 
    94     </itemizedlist>
    95 
    96   </sect2>
    97 <!--
    98   <sect2 id='sysd-desc'>
    99     <title>Systemd</title>
    100 
    101     <para>Systemd is a group of interconnected programs that handles system and
    102     individual process requests.  It provides a dependency system between
    103     various entities called "units".  It automatically addresses dependencies
    104     between units and can execute several startup tasks in parallel.  It
    105     provides login, inetd, logging, time, and networking services. </para>
    106 
    107     <bridgehead renderas="sect3">Advantages</bridgehead>
    108 
    109     <itemizedlist>
    110       <listitem>
    111           <para>Used on many established distributions by default.</para>
    112       </listitem>
    113 
    114       <listitem>
    115           <para>There is extensive documentation.
    116           See <ulink url="http://www.freedesktop.org/wiki/Software/systemd/"/>.</para>
    117       </listitem>
    118 
    119       <listitem>
    120           <para>Parallel execution of boot processes. A medium speed
    121           base LFS system takes 6-10 seconds from kernel start to a
    122           login prompt.  Network connectivity is typically established
    123           about 2 seconds after the login prompt.  More complex startup
    124           procedures may show a greater speedup when compared to System V.</para>
    125       </listitem>
    126 
    127       <listitem>
    128           <para>Implements advanced features such as control groups to
    129           manage related processes.</para>
    130       </listitem>
    131 
    132       <listitem>
    133           <para>Maintains backward compatibility with System V programs
    134           and scripts.</para>
    135       </listitem>
    136     </itemizedlist>
    137 
    138     <bridgehead renderas="sect3">Disadvantages</bridgehead>
    139 
    140     <itemizedlist>
    141       <listitem>
    142           <para>There is a substantial learning curve.</para>
    143       </listitem>
    144 
    145       <listitem>
    146           <para>Some advanced features such as dbus or cgroups cannot be
    147           disabled if they are not otherwise needed.</para>
    148       </listitem>
    149 
    150       <listitem>
    151           <para>Although implemented as several executable programs
    152           the user cannot choose to implement only the portions desired.</para>
    153       </listitem>
    154 
    155       <listitem>
    156           <para>Due to the nature of using compiled programs, systemd is
    157           more difficult to debug.</para>
    158       </listitem>
    159 
    160       <listitem>
    161           <para>Logging is done in a binary format.  Extra tools must
    162           be used to process logs or additional processes must be implemented
    163           to duplicate traditional logging programs.</para>
    164       </listitem>
    165 
    166     </itemizedlist>
    167 
    168   </sect2>
    169 -->
    170 <!--
    171   <sect2 id='sysv'>
    172     <title>Selecting a Boot Method</title>
    173 
    174     <para>Selecting a boot method in LFS is relatively easy. 
    175     Both systems are installed side-by-side.  The only task needed is to
    176     ensure the files that are needed by the system have the correct names.
    177     The following scripts do that.</para>
    178 
    179 <screen><userinput remap="install">cat &gt; /usr/sbin/set-systemd &lt;&lt; "EOF"
    180 #! /bin/bash
    181 
    182 ln -svfn init-systemd   /sbin/init
    183 ln -svfn init.d-systemd /etc/init.d
    184 
    185 for tool in halt poweroff reboot runlevel shutdown telinit; do
    186   ln -sfvn  ${tool}-systemd   /sbin/${tool}
    187   ln -svfn  ${tool}-systemd.8 /usr/share/man/man8/${tool}.8
    188 done
    189 
    190 echo "Now reboot with /sbin/reboot-sysv"
    191 EOF
    192 
    193 chmod 0744 /usr/sbin/set-systemd
    194 
    195 cat &gt; /usr/sbin/set-sysv &lt;&lt; "EOF"
    196 #! /bin/bash
    197 
    198 ln -sfvn init-sysv    /sbin/init
    199 ln -svfn init.d-sysv  /etc/init.d
    200 
    201 for tool in halt poweroff reboot runlevel shutdown telinit; do
    202   ln -sfvn  ${tool}-sysv   /sbin/${tool}
    203   ln -svfn  ${tool}-sysv.8 /usr/share/man/man8/${tool}.8
    204 done
    205 
    206 echo "Now reboot with /sbin/reboot-systemd"
    207 EOF
    208 
    209 chmod 0744 /usr/sbin/set-sysv</userinput></screen>
    210 
    211   <note><para>The comment about the correct command to reboot in the
    212   above scripts is correct.  The reboot command for the current boot
    213   system must be used after the script changes the default reboot command.
    214   </para></note>
    215 
    216   <para>Now set the desired boot system.  The default is System V:</para>
    217 
    218 <screen><userinput remap="install">/usr/sbin/set-sysv</userinput></screen>
    219 
    220   <para>Changing the boot system can be done at any time by running the
    221   appropriate script above and rebooting.</para>
    222 
    223   </sect2>
    224 -->
    22533</sect1>
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