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diff --git a/chapter07/introduction.xml b/chapter07/introduction.xml index cbc197a7b..5614270b2 100644 --- a/chapter07/introduction.xml +++ b/chapter07/introduction.xml @@ -5,221 +5,25 @@ %general-entities; ]> -<sect1 id="ch-config-introduction" revision="sysv"> +<sect1 id="ch-tools-introduction"> <?dbhtml filename="introduction.html"?> <title>Introduction</title> - <para>Booting a Linux system involves several tasks. The process must - mount both virtual and real file systems, initialize devices, activate swap, - check file systems for integrity, mount any swap partitions or files, set - the system clock, bring up networking, start any daemons required by the - system, and accomplish any other custom tasks needed by the user. This - process must be organized to ensure the tasks are performed in the correct - order but, at the same time, be executed as fast as possible.</para> + <para>This chapter shows how to build a minimal Linux system. + This system will contain just enough tools to start constructing the final + LFS system in <xref linkend="chapter-building-system"/> and allow a working + environment with more user convenience than a minimum environment would.</para> -<!-- <para>In the packages that were installed in Chapter 6, there were two - different boot systems installed. LFS provides the ability to easily - select which system the user wants to use and to compare and contrast the - two systems by actually running each system on the local computer. The - advantages and disadvantages of these systems is presented below.</para>--> - - <sect2 id='sysv-desc'> - <title>System V</title> - - <para>System V is the classic boot process that has been used in Unix and - Unix-like systems such as Linux since about 1983. It consists of a small - program, <command>init</command>, that sets up basic programs such as - <command>login</command> (via getty) and runs a script. This script, - usually named <command>rc</command>, controls the execution of a set of - additional scripts that perform the tasks required to initialize the - system.</para> - - <para>The <command>init</command> program is controlled by the - <filename>/etc/inittab</filename> file and is organized into run levels that - can be run by the user:</para> - -<literallayout> -0 — halt -1 — Single user mode -2 — Multiuser, without networking -3 — Full multiuser mode -4 — User definable -5 — Full multiuser mode with display manager -6 — reboot -</literallayout> - - <para>The usual default run level is 3 or 5.</para> - - <bridgehead renderas="sect3">Advantages</bridgehead> - - <itemizedlist> - <listitem> - <para>Established, well understood system.</para> - </listitem> - - <listitem> - <para>Easy to customize.</para> - </listitem> - - </itemizedlist> - - - <bridgehead renderas="sect3">Disadvantages</bridgehead> - - <itemizedlist> - <listitem> - <para>Slower to boot. A medium speed base LFS system - takes 8-12 seconds where the boot time is measured from the - first kernel message to the login prompt. Network - connectivity is typically established about 2 seconds - after the login prompt.</para> - </listitem> - - <listitem> - <para>Serial processing of boot tasks. This is related to the previous - point. A delay in any process such as a file system check, will - delay the entire boot process.</para> - </listitem> - - <listitem> - <para>Does not directly support advanced features like - control groups (cgroups), and per-user fair share scheduling.</para> - </listitem> - - <listitem> - <para>Adding scripts requires manual, static sequencing decisions.</para> - </listitem> - - </itemizedlist> - - </sect2> -<!-- - <sect2 id='sysd-desc'> - <title>Systemd</title> - - <para>Systemd is a group of interconnected programs that handles system and - individual process requests. It provides a dependency system between - various entities called "units". It automatically addresses dependencies - between units and can execute several startup tasks in parallel. It - provides login, inetd, logging, time, and networking services. </para> - - <bridgehead renderas="sect3">Advantages</bridgehead> - - <itemizedlist> - <listitem> - <para>Used on many established distributions by default.</para> - </listitem> - - <listitem> - <para>There is extensive documentation. - See <ulink url="http://www.freedesktop.org/wiki/Software/systemd/"/>.</para> - </listitem> - - <listitem> - <para>Parallel execution of boot processes. A medium speed - base LFS system takes 6-10 seconds from kernel start to a - login prompt. Network connectivity is typically established - about 2 seconds after the login prompt. More complex startup - procedures may show a greater speedup when compared to System V.</para> - </listitem> - - <listitem> - <para>Implements advanced features such as control groups to - manage related processes.</para> - </listitem> - - <listitem> - <para>Maintains backward compatibility with System V programs - and scripts.</para> - </listitem> - </itemizedlist> - - <bridgehead renderas="sect3">Disadvantages</bridgehead> - - <itemizedlist> - <listitem> - <para>There is a substantial learning curve.</para> - </listitem> - - <listitem> - <para>Some advanced features such as dbus or cgroups cannot be - disabled if they are not otherwise needed.</para> - </listitem> - - <listitem> - <para>Although implemented as several executable programs - the user cannot choose to implement only the portions desired.</para> - </listitem> - - <listitem> - <para>Due to the nature of using compiled programs, systemd is - more difficult to debug.</para> - </listitem> - - <listitem> - <para>Logging is done in a binary format. Extra tools must - be used to process logs or additional processes must be implemented - to duplicate traditional logging programs.</para> - </listitem> - - </itemizedlist> - - </sect2> ---> + <para>There are two steps in building this minimal system. The first step + is to build a new and host-independent toolchain (compiler, assembler, + linker, libraries, and a few useful utilities). The second step uses this + toolchain to build the other essential tools.</para> <!-- - <sect2 id='sysv'> - <title>Selecting a Boot Method</title> - - <para>Selecting a boot method in LFS is relatively easy. - Both systems are installed side-by-side. The only task needed is to - ensure the files that are needed by the system have the correct names. - The following scripts do that.</para> - -<screen><userinput remap="install">cat > /usr/sbin/set-systemd << "EOF" -#! /bin/bash - -ln -svfn init-systemd /sbin/init -ln -svfn init.d-systemd /etc/init.d - -for tool in halt poweroff reboot runlevel shutdown telinit; do - ln -sfvn ${tool}-systemd /sbin/${tool} - ln -svfn ${tool}-systemd.8 /usr/share/man/man8/${tool}.8 -done - -echo "Now reboot with /sbin/reboot-sysv" -EOF - -chmod 0744 /usr/sbin/set-systemd - -cat > /usr/sbin/set-sysv << "EOF" -#! /bin/bash - -ln -sfvn init-sysv /sbin/init -ln -svfn init.d-sysv /etc/init.d - -for tool in halt poweroff reboot runlevel shutdown telinit; do - ln -sfvn ${tool}-sysv /sbin/${tool} - ln -svfn ${tool}-sysv.8 /usr/share/man/man8/${tool}.8 -done - -echo "Now reboot with /sbin/reboot-systemd" -EOF - -chmod 0744 /usr/sbin/set-sysv</userinput></screen> - - <note><para>The comment about the correct command to reboot in the - above scripts is correct. The reboot command for the current boot - system must be used after the script changes the default reboot command. - </para></note> - - <para>Now set the desired boot system. The default is System V:</para> - -<screen><userinput remap="install">/usr/sbin/set-sysv</userinput></screen> - - <para>Changing the boot system can be done at any time by running the - appropriate script above and rebooting.</para> - - </sect2> + <para>The files compiled in this chapter will be installed under the + <filename class="directory">$LFS</filename> directory to keep them + separate from the files installed in the next chapter and the host + production directories. Since the packages compiled here are temporary, + we do not want them to pollute the soon-to-be LFS system.</para> --> </sect1> |