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Timestamp:
04/03/2014 09:52:09 PM (10 years ago)
Author:
Bruce Dubbs <bdubbs@…>
Branches:
10.0, 10.0-rc1, 10.1, 10.1-rc1, 11.0, 11.0-rc1, 11.0-rc2, 11.0-rc3, 11.1, 11.1-rc1, 11.2, 11.2-rc1, 11.3, 11.3-rc1, 12.0, 12.0-rc1, 12.1, 12.1-rc1, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 9.0, 9.1, arm, bdubbs/gcc13, ml-11.0, multilib, renodr/libudev-from-systemd, s6-init, trunk, xry111/arm64, xry111/arm64-12.0, xry111/clfs-ng, xry111/lfs-next, xry111/loongarch, xry111/loongarch-12.0, xry111/loongarch-12.1, xry111/mips64el, xry111/pip3, xry111/rust-wip-20221008, xry111/update-glibc
Children:
9839808
Parents:
008436e
Message:

Added systemd and dbus to the book.
Set up systemd and System V side-by-side with the
ability to reboot to either system.

git-svn-id: ​http://svn.linuxfromscratch.org/LFS/trunk/BOOK@10520 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

File:
1 edited

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  • chapter07/introduction.xml

    r008436e rcba2d4e  
    1111  <title>Introduction</title>
    1212
    13   <para>This chapter discusses configuration files and boot scripts.
    14   First, the general configuration files needed to set up networking are
    15   presented.</para>
    16 
    17   <itemizedlist>
    18      <listitem>
    19        <para><xref linkend="ch-scripts-network" role="."/></para>
    20      </listitem>
    21      <listitem>
    22        <para><xref linkend="ch-scripts-hosts" role="."/></para>
    23      </listitem>
    24   </itemizedlist>
    25 
    26   <para>Second, issues that affect the proper setup of devices are
    27   discussed.</para>
    28 
    29   <itemizedlist>
    30      <listitem>
    31        <para><xref linkend="ch-scripts-udev" role="."/></para>
    32      </listitem>
    33      <listitem>
    34        <para><xref linkend="ch-scripts-symlinks" role="."/></para>
    35      </listitem>
    36   </itemizedlist>
    37 
    38   <para>The next sections detail how to install and configure the LFS system
    39   scripts needed during the boot process. Most of these scripts will work
    40   without modification, but a few require additional configuration files
    41   because they deal with hardware-dependent information.</para>
    42 
    43   <para>System-V style init scripts are employed in this book because they are
    44   widely used and relatively simple. For additional options, a hint detailing
    45   the BSD style init setup is available at <ulink
    46   url="&hints-root;bsd-init.txt"/>.  Searching the LFS mailing lists for
    47   <quote>depinit</quote>, <quote>upstart</quote>, or <quote>systemd</quote>
    48   will also offer additional information.</para>
    49 
    50   <para>If using an alternative style of init scripts, skip these sections.</para>
    51 
    52   <para>A listing of the boot scripts are found in <xref linkend="scripts"
    53   role="."/>.</para>
    54 
    55 
    56   <itemizedlist>
    57      <listitem>
    58        <para><xref linkend="ch-scripts-bootscripts" role="."/></para>
    59      </listitem>
    60      <listitem>
    61        <para><xref linkend="ch-scripts-usage" role="."/></para>
    62      </listitem>
    63      <listitem>
    64        <para><xref linkend="ch-scripts-hostname" role="."/></para>
    65      </listitem>
    66      <listitem>
    67        <para><xref linkend="ch-scripts-setclock" role="."/></para>
    68      </listitem>
    69      <listitem>
    70        <para><xref linkend="ch-scripts-console" role="."/></para>
    71      </listitem>
    72      <listitem>
    73        <para><xref linkend="ch-scripts-sysklogd" role="."/></para>
    74      </listitem>
    75   </itemizedlist>
    76 
    77 
    78   <para>Finally, there is a brief introduction to the scripts and configuration
    79   files used when the user logs into the system.</para>
    80 
    81   <itemizedlist>
    82      <listitem>
    83        <para><xref linkend="ch-scripts-profile" role="."/></para>
    84      </listitem>
    85      <listitem>
    86        <para><xref linkend="ch-scripts-inputrc" role="."/></para>
    87      </listitem>
    88   </itemizedlist>
    89 
     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>
     20
     21    <para>In the packages that were installed in Chapter 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>
     26
     27  <sect2 id='sysv-desc'>
     28    <title>System V</title>
     29
     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    <itemizedlist>
     43      <listitem><para>0 &mdash; halt</para></listitem>
     44      <listitem><para>1 &mdash; Single user mode</para></listitem>
     45      <listitem><para>2 &mdash; Multiuser, without networking</para></listitem>
     46      <listitem><para>3 &mdash; Full multiuser mode</para></listitem>
     47      <listitem><para>4 &mdash; User definable</para></listitem>
     48      <listitem><para>5 &mdash; Full multiuser mode with display manager</para></listitem>
     49      <listitem><para>6 &mdash; reboot</para></listitem>
     50    </itemizedlist>
     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  <sect2 id='sysv'>
     171    <title>Selecting a Boot Method</title>
     172
     173    <para>Selecting a boot method in LFS is relatively easy. 
     174    Both systems are installed side-by-side.  The only task needed is to
     175    ensure the files that are needed by the system have the correct names.
     176    The following scripts do that.</para>
     177
     178<screen><userinput remap="install">cat &gt; /usr/local/sbin/set-systemd &lt;&lt; "EOF"
     179#! /bin/bash
     180
     181ln -svfn init-systemd   /sbin/init
     182ln -svfn init.d-systemd /etc/init.d
     183
     184for tool in halt poweroff reboot runlevel shutdown telinit; do
     185  ln -sfvn  $(tool}-systemd   /sbin/${tool}
     186  ln -svfn  ${tool}-systemd.8 /usr/share/man/man8/${tool}.8
     187done
     188
     189echo "Now reboot with /sbin/reboot-sysv"
     190EOF
     191
     192chmod 0744 /usr/local/sbin/set-systemd
     193
     194cat &gt; /usr/local/sbin/set-sysv &lt;&lt; "EOF"
     195ln -sfvn init-sysv    /sbin/init
     196ln -svfn init.d-sysv  /etc/init.d
     197
     198for tool in halt poweroff reboot runlevel shutdown telinit; do
     199  ln -sfvn  ${tool}-sysv   /sbin/${tool}
     200  ln -svfn  ${tool}-sysv.8 /usr/share/man/man8/${tool}.8
     201done
     202
     203echo "Now reboot with /sbin/reboot-systemd"
     204EOF
     205
     206chmod 0744 /usr/local/sbin/set-sysv</userinput></screen>
     207
     208  <para>Now set the desired boot system.  The default is System V:</para>
     209
     210<screen><userinput remap="install">/usr/local/sbin/set-sysv</userinput></screen>
     211
     212  <para>Changing the boot system can be done at any time by running the
     213  appropriate script above and rebooting.</para>
     214
     215  </sect2>
    90216
    91217</sect1>
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