source: chapter04/settingenviron.xml@ efcb393

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Make the new book

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1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3 "" [
4 <!ENTITY % general-entities SYSTEM "../general.ent">
5 %general-entities;
8<sect1 id="ch-preps-settingenviron">
9 <?dbhtml filename="settingenvironment.html"?>
11 <title>Setting Up the Environment</title>
13 <para>Set up a good working environment by creating two new startup files
14 for the <command>bash</command> shell. While logged in as user
15 <systemitem class="username">lfs</systemitem>, issue the following command
16 to create a new <filename>.bash_profile</filename>:</para>
18<screen><userinput>cat &gt; ~/.bash_profile &lt;&lt; "EOF"
19<literal>exec env -i HOME=$HOME TERM=$TERM PS1='\u:\w\$ ' /bin/bash</literal>
22 <para>When logged on as user <systemitem class="username">lfs</systemitem>,
23 the initial shell is usually a <emphasis>login</emphasis> shell which reads
24 the <filename>/etc/profile</filename> of the host (probably containing some
25 settings and environment variables) and then <filename>.bash_profile</filename>.
26 The <command>exec env -i.../bin/bash</command> command in the
27 <filename>.bash_profile</filename> file replaces the running shell with a new
28 one with a completely empty environment, except for the <envar>HOME</envar>,
29 <envar>TERM</envar>, and <envar>PS1</envar> variables. This ensures that no
30 unwanted and potentially hazardous environment variables from the host system
31 leak into the build environment. The technique used here achieves the goal of
32 ensuring a clean environment.</para>
34 <para>The new instance of the shell is a <emphasis>non-login</emphasis>
35 shell, which does not read, and execute, the conten of <filename>/etc/profile</filename> or
36 <filename>.bash_profile</filename> files, but rather reads, and executes, the
37 <filename>.bashrc</filename> file instead. Create the
38 <filename>.bashrc</filename> file now:</para>
40<screen><userinput>cat &gt; ~/.bashrc &lt;&lt; "EOF"
41<literal>set +h
42umask 022
45LFS_TGT=$(uname -m)-lfs-linux-gnu
47export LFS LC_ALL LFS_TGT PATH</literal>
50 <variablelist>
51 <title>The meaning of the command line options in <filename>.bashrc</filename></title>
53 <varlistentry>
54 <term><parameter>set +h</parameter></term>
55 <listitem>
56 <para>The <command>set +h</command> command turns off
57 <command>bash</command>'s hash function. Hashing is ordinarily a useful
58 feature&mdash;<command>bash</command> uses a hash table to remember the
59 full path of executable files to avoid searching the <envar>PATH</envar>
60 time and again to find the same executable. However, the new tools should
61 be used as soon as they are installed. By switching off the hash function,
62 the shell will always search the <envar>PATH</envar> when a program is to
63 be run. As such, the shell will find the newly compiled tools in
64 <filename class="directory">~/tools</filename> as soon as they are
65 available without remembering a previous version of the same program in a
66 different location.</para>
67 </listitem>
68 </varlistentry>
70 <varlistentry>
71 <term><parameter>umask 022</parameter></term>
72 <listitem>
73 <para>Setting the user file-creation mask (umask) to 022 ensures that newly
74 created files and directories are only writable by their owner, but are
75 readable and executable by anyone (assuming default modes are used by the
76 <function>open(2)</function> system call, new files will end up with permission
77 mode 644 and directories with mode 755).</para>
78 </listitem>
79 </varlistentry>
81 <varlistentry>
82 <term><parameter>LFS=/mnt/lfs</parameter></term>
83 <listitem>
84 <para>The <envar>LFS</envar> variable should be set to the chosen mount
85 point.</para>
86 </listitem>
87 </varlistentry>
89 <varlistentry>
90 <term><parameter>LC_ALL=POSIX</parameter></term>
91 <listitem>
92 <para>The <envar>LC_ALL</envar> variable controls the localization of certain
93 programs, making their messages follow the conventions of a specified country.
94 Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
95 (the two are equivalent) ensures that everything will work as expected in
96 the chroot environment.</para>
97 </listitem>
98 </varlistentry>
100 <varlistentry>
101 <term><parameter>LFS_TGT=(uname -m)-lfs-linux-gnu</parameter></term>
102 <listitem>
103 <para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
104 description for use when building our cross compiler and linker and when cross
105 compiling our temporary toolchain. More information is contained in
106 <xref linkend="ch-tools-toolchaintechnotes" role=""/>.</para>
107 </listitem>
108 </varlistentry>
110 <varlistentry>
111 <term><parameter>PATH=$LFS/tools/bin:/bin:/usr/bin</parameter></term>
112 <listitem>
113 <para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
114 standard <envar>PATH</envar>, all the programs installed in <xref
115 linkend="chapter-temporary-tools"/> are picked up by the shell immediately after
116 their installation. This, combined with turning off hashing, limits the risk
117 that old programs are used from the host when the same programs are available in
118 the Chapter 5 environment.</para>
119 </listitem>
120 </varlistentry>
122 <varlistentry>
123 <term><parameter>export LFS LC_ALL LFS_TGT PATH</parameter></term>
124 <listitem>
125 <para>While the above commands have set some variables, in order
126 to make them visible within any sub-shells, we export them</para>
127 </listitem>
128 </varlistentry>
130 </variablelist>
132 <para>Finally, to have the environment fully prepared for building the
133 temporary tools, source the just-created user profile:</para>
135<screen><userinput>source ~/.bash_profile</userinput></screen>
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