source: chapter04/settingenviron.xml

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Last change on this file was 4e26453, checked in by David Bryant <davidbryant@…>, 3 months ago

Standardize spelling of "cross-compile" and its derivatives. Clean up
English idiom. Remove some superfluous verbiage here and there.

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File size: 8.8 KB
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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 or when switched to the &lfs-user; user using an <command>su</command> command
24 with the <quote><parameter>-</parameter></quote> option,
25 the initial shell is a <emphasis>login</emphasis> shell which reads
26 the <filename>/etc/profile</filename> of the host (probably containing some
27 settings and environment variables) and then <filename>.bash_profile</filename>.
28 The <command>exec env -i.../bin/bash</command> command in the
29 <filename>.bash_profile</filename> file replaces the running shell with a new
30 one with a completely empty environment, except for the <envar>HOME</envar>,
31 <envar>TERM</envar>, and <envar>PS1</envar> variables. This ensures that no
32 unwanted and potentially hazardous environment variables from the host system
33 leak into the build environment.</para>
34
35 <para>The new instance of the shell is a <emphasis>non-login</emphasis>
36 shell, which does not read, and execute, the contents of the <filename>/etc/profile</filename> or
37 <filename>.bash_profile</filename> files, but rather reads, and executes, the
38 <filename>.bashrc</filename> file instead. Create the
39 <filename>.bashrc</filename> file now:</para>
40
41<screen><userinput>cat &gt; ~/.bashrc &lt;&lt; "EOF"
42<literal>set +h
43umask 022
44LFS=/mnt/lfs
45LC_ALL=POSIX
46LFS_TGT=$(uname -m)-lfs-linux-gnu
47PATH=/usr/bin
48if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
49PATH=$LFS/tools/bin:$PATH
50CONFIG_SITE=$LFS/usr/share/config.site
51export LFS LC_ALL LFS_TGT PATH CONFIG_SITE</literal>
52EOF</userinput></screen>
53
54 <variablelist>
55 <title>The meaning of the settings in <filename>.bashrc</filename></title>
56
57 <varlistentry>
58 <term><parameter>set +h</parameter></term>
59 <listitem>
60 <para>The <command>set +h</command> command turns off
61 <command>bash</command>'s hash function. Hashing is ordinarily a useful
62 feature&mdash;<command>bash</command> uses a hash table to remember the
63 full path to executable files to avoid searching the <envar>PATH</envar>
64 time and again to find the same executable. However, the new tools should
65 be used as soon as they are installed. Switching off the hash function forces
66 the shell to search the <envar>PATH</envar> whenever a program is to
67 be run. As such, the shell will find the newly compiled tools in
68 <filename class="directory">$LFS/tools/bin</filename> as soon as they are
69 available without remembering a previous version of the same program
70 provided by the host distro, in
71 <filename class='directory'>/usr/bin</filename> or
72 <filename class='directory'>/bin</filename>.</para>
73 </listitem>
74 </varlistentry>
75
76 <varlistentry>
77 <term><parameter>umask 022</parameter></term>
78 <listitem>
79 <para>Setting the user file-creation mask (umask) to 022 ensures that newly
80 created files and directories are only writable by their owner, but are
81 readable and executable by anyone (assuming default modes are used by the
82 <function>open(2)</function> system call, new files will end up with permission
83 mode 644 and directories with mode 755).</para>
84 </listitem>
85 </varlistentry>
86
87 <varlistentry>
88 <term><parameter>LFS=/mnt/lfs</parameter></term>
89 <listitem>
90 <para>The <envar>LFS</envar> variable should be set to the chosen mount
91 point.</para>
92 </listitem>
93 </varlistentry>
94
95 <varlistentry>
96 <term><parameter>LC_ALL=POSIX</parameter></term>
97 <listitem>
98 <para>The <envar>LC_ALL</envar> variable controls the localization of certain
99 programs, making their messages follow the conventions of a specified country.
100 Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
101 (the two are equivalent) ensures that everything will work as expected in
102 the cross-compilation environment.</para>
103 </listitem>
104 </varlistentry>
105
106 <varlistentry>
107 <term><parameter>LFS_TGT=(uname -m)-lfs-linux-gnu</parameter></term>
108 <listitem>
109 <para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
110 description for use when building our cross-compiler and linker and when
111 cross-compiling our temporary toolchain. More information is provided by
112 <xref linkend="ch-tools-toolchaintechnotes" role=""/>.</para>
113 </listitem>
114 </varlistentry>
115
116 <varlistentry>
117 <term><parameter>PATH=/usr/bin</parameter></term>
118 <listitem>
119 <para>Many modern Linux distributions have merged <filename
120 class="directory">/bin</filename> and <filename
121 class="directory">/usr/bin</filename>. When this is the case, the standard
122 <envar>PATH</envar> variable should be set to <filename
123 class="directory">/usr/bin/</filename> for the <xref
124 linkend="chapter-temporary-tools"/> environment. When this is not the
125 case, the following line adds <filename class="directory">/bin</filename>
126 to the path.</para>
127 </listitem>
128 </varlistentry>
129
130 <varlistentry>
131 <term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
132 <listitem>
133 <para>If <filename class="directory">/bin</filename> is not a symbolic
134 link, it must be added to the <envar>PATH</envar> variable.</para>
135 </listitem>
136 </varlistentry>
137
138 <varlistentry>
139 <term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
140 <listitem>
141 <para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
142 standard <envar>PATH</envar>, the cross-compiler installed at the beginning
143 of <xref linkend="chapter-cross-tools"/> is picked up by the shell
144 immediately after its installation. This, combined with turning off hashing,
145 limits the risk that the compiler from the host is used instead of the
146 cross-compiler.</para>
147 </listitem>
148 </varlistentry>
149
150 <varlistentry>
151 <term><parameter>CONFIG_SITE=$LFS/usr/share/config.site</parameter></term>
152 <listitem>
153 <para>In <xref linkend="chapter-cross-tools"/> and
154 <xref linkend="chapter-temporary-tools"/>, if this variable is not set,
155 <command>configure</command> scripts
156 may attempt to load configuration items specific to some distributions from
157 <filename>/usr/share/config.site</filename> on the host system. Override
158 it to prevent potential contamination from the host.</para>
159 </listitem>
160 </varlistentry>
161
162 <varlistentry>
163 <term><parameter>export ...</parameter></term>
164 <listitem>
165 <para>While the preceding commands have set some variables, in order
166 to make them visible within any sub-shells, we export them.</para>
167 </listitem>
168 </varlistentry>
169
170 </variablelist>
171
172 <important>
173
174 <para>Several commercial distributions add an undocumented instantiation
175 of <filename>/etc/bash.bashrc</filename> to the initialization of
176 <command>bash</command>. This file has the potential to modify the
177 <systemitem class="username">lfs</systemitem>
178 user's environment in ways that can affect the building of critical LFS
179 packages. To make sure the <systemitem class="username">lfs</systemitem>
180 user's environment is clean, check for the
181 presence of <filename>/etc/bash.bashrc</filename> and, if present, move it
182 out of the way. As the <systemitem class="username">root</systemitem>
183 user, run:</para>
184
185 <screen role="nodump"><userinput>[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
186
187 <para>When the <systemitem class="username">lfs</systemitem>
188 user is no longer needed (at the beginning of <xref
189 linkend="chapter-chroot-temporary-tools"/>), you may safely restore
190 <filename>/etc/bash.bashrc</filename> (if desired).</para>
191
192 <para>Note that the LFS Bash package we will build in
193 <xref linkend="ch-system-bash"/> is not configured to load or execute
194 <filename>/etc/bash.bashrc</filename>, so this file is useless on a
195 completed LFS system.</para>
196 </important>
197
198 <para>Finally, to ensure the environment is fully prepared for building the
199 temporary tools, force the <command>bash</command> shell to read
200 the new user profile:</para>
201
202<screen><userinput>source ~/.bash_profile</userinput></screen>
203
204</sect1>
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