source: chapter04/settingenviron.xml@ 686c88b

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Last change on this file since 686c88b was 686c88b, checked in by Bruce Dubbs <bdubbs@…>, 18 months ago

Add a note about /etc/bash.bashrc used in some distros.
Tweak css for appendix/dependencies.

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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 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4 <!ENTITY % general-entities SYSTEM "../general.ent">
5 %general-entities;
6]>
7
8<sect1 id="ch-preps-settingenviron">
9 <?dbhtml filename="settingenvironment.html"?>
10
11 <title>Setting Up the Environment</title>
12
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>
17
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>
20EOF</userinput></screen>
21
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>
33
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>
39
40<screen><userinput>cat &gt; ~/.bashrc &lt;&lt; "EOF"
41<literal>set +h
42umask 022
43LFS=/mnt/lfs
44LC_ALL=POSIX
45LFS_TGT=$(uname -m)-lfs-linux-gnu
46PATH=/usr/bin
47if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
48PATH=$LFS/tools/bin:$PATH
49export LFS LC_ALL LFS_TGT PATH</literal>
50EOF</userinput></screen>
51
52 <variablelist>
53 <title>The meaning of the settings in <filename>.bashrc</filename></title>
54
55 <varlistentry>
56 <term><parameter>set +h</parameter></term>
57 <listitem>
58 <para>The <command>set +h</command> command turns off
59 <command>bash</command>'s hash function. Hashing is ordinarily a useful
60 feature&mdash;<command>bash</command> uses a hash table to remember the
61 full path of executable files to avoid searching the <envar>PATH</envar>
62 time and again to find the same executable. However, the new tools should
63 be used as soon as they are installed. By switching off the hash function,
64 the shell will always search the <envar>PATH</envar> when a program is to
65 be run. As such, the shell will find the newly compiled tools in
66 <filename class="directory">$LFS/tools</filename> as soon as they are
67 available without remembering a previous version of the same program in a
68 different location.</para>
69 </listitem>
70 </varlistentry>
71
72 <varlistentry>
73 <term><parameter>umask 022</parameter></term>
74 <listitem>
75 <para>Setting the user file-creation mask (umask) to 022 ensures that newly
76 created files and directories are only writable by their owner, but are
77 readable and executable by anyone (assuming default modes are used by the
78 <function>open(2)</function> system call, new files will end up with permission
79 mode 644 and directories with mode 755).</para>
80 </listitem>
81 </varlistentry>
82
83 <varlistentry>
84 <term><parameter>LFS=/mnt/lfs</parameter></term>
85 <listitem>
86 <para>The <envar>LFS</envar> variable should be set to the chosen mount
87 point.</para>
88 </listitem>
89 </varlistentry>
90
91 <varlistentry>
92 <term><parameter>LC_ALL=POSIX</parameter></term>
93 <listitem>
94 <para>The <envar>LC_ALL</envar> variable controls the localization of certain
95 programs, making their messages follow the conventions of a specified country.
96 Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
97 (the two are equivalent) ensures that everything will work as expected in
98 the chroot environment.</para>
99 </listitem>
100 </varlistentry>
101
102 <varlistentry>
103 <term><parameter>LFS_TGT=(uname -m)-lfs-linux-gnu</parameter></term>
104 <listitem>
105 <para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
106 description for use when building our cross compiler and linker and when cross
107 compiling our temporary toolchain. More information is contained in
108 <xref linkend="ch-tools-toolchaintechnotes" role=""/>.</para>
109 </listitem>
110 </varlistentry>
111
112 <varlistentry>
113 <term><parameter>PATH=/usr/bin</parameter></term>
114 <listitem>
115 <para>Many modern linux distributions have merged <filename
116 class="directory">/bin</filename> and <filename
117 class="directory">/usr/bin</filename>. When this is the case, the standard
118 <envar>PATH</envar> variable needs just to be set to <filename
119 class="directory">/usr/bin/</filename> for the <xref
120 linkend="chapter-temporary-tools"/> environment. When this is not the
121 case, the following line adds <filename class="directory">/bin</filename>
122 to the path.</para>
123 </listitem>
124 </varlistentry>
125
126 <varlistentry>
127 <term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
128 <listitem>
129 <para>If <filename class="directory">/bin</filename> is not a symbolic
130 link, then it has to be added to the <envar>PATH</envar> variable.</para>
131 </listitem>
132 </varlistentry>
133
134 <varlistentry>
135 <term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
136 <listitem>
137 <para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
138 standard <envar>PATH</envar>, the cross-compiler installed at the beginning
139 of <xref linkend="chapter-cross-tools"/> is picked up by the shell
140 immediately after its installation. This, combined with turning off hashing,
141 limits the risk that the compiler from the host be used instead of the
142 cross-compiler.</para>
143 </listitem>
144 </varlistentry>
145
146 <varlistentry>
147 <term><parameter>export LFS LC_ALL LFS_TGT PATH</parameter></term>
148 <listitem>
149 <para>While the above commands have set some variables, in order
150 to make them visible within any sub-shells, we export them.</para>
151 </listitem>
152 </varlistentry>
153
154 </variablelist>
155
156 <important>
157
158 <para>Several commercial distributions add a non-documented instantiation
159 of <filename>/etc/bash.bashrc</filename> to the initialization of
160 <command>bash</command>. This file has the potential to modify the lfs
161 user's envirnment in ways that can affect the building of critical LFS
162 packages. To make sure the lfs user's envronment is clean, check for the
163 presence of <filename>/etc/bash.bashrc</filename> and, if present, move it
164 out of the way. As the root user, run:</para>
165
166 <screen role="nodump"><userinput>mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
167
168 <para>After use of the lfs user is finished at the end of <xref
169 linkend="chapter-chroot-temporary-tools"/>, you can restore
170 <filename>/etc/bash.bashrc</filename> (if desired).</para>
171 </important>
172
173 <para>Finally, to have the environment fully prepared for building the
174 temporary tools, source the just-created user profile:</para>
175
176<screen><userinput>source ~/.bash_profile</userinput></screen>
177
178</sect1>
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