source: chapter04/settingenviron.xml@ 0bd1c05

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Last change on this file since 0bd1c05 was 0bd1c05, checked in by Xi Ruoyao <xry111@…>, 10 months ago

cross-ng: chapter 4: set LFS_TGT for target machine

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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 contents 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=<replaceable>x86_64</replaceable>-lfs-linux-gnu
46PATH=/usr/bin
47if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
48PATH=$LFS/tools/bin:$PATH
49CONFIG_SITE=$LFS/usr/share/config.site
50export LFS LC_ALL LFS_TGT PATH CONFIG_SITE</literal>
51EOF</userinput></screen>
52
53 <variablelist>
54 <title>The meaning of the settings in <filename>.bashrc</filename></title>
55
56 <varlistentry>
57 <term><parameter>set +h</parameter></term>
58 <listitem>
59 <para>The <command>set +h</command> command turns off
60 <command>bash</command>'s hash function. Hashing is ordinarily a useful
61 feature&mdash;<command>bash</command> uses a hash table to remember the
62 full path of executable files to avoid searching the <envar>PATH</envar>
63 time and again to find the same executable. However, the new tools should
64 be used as soon as they are installed. By switching off the hash function,
65 the shell will always search the <envar>PATH</envar> when a program is to
66 be run. As such, the shell will find the newly compiled tools in
67 <filename class="directory">$LFS/tools/bin</filename> as soon as they are
68 available without remembering a previous version of the same program
69 provided by the host distro, in
70 <filename class='directory'>/usr/bin</filename> or
71 <filename class='directory'>/bin</filename>.</para>
72 </listitem>
73 </varlistentry>
74
75 <varlistentry>
76 <term><parameter>umask 022</parameter></term>
77 <listitem>
78 <para>Setting the user file-creation mask (umask) to 022 ensures that newly
79 created files and directories are only writable by their owner, but are
80 readable and executable by anyone (assuming default modes are used by the
81 <function>open(2)</function> system call, new files will end up with permission
82 mode 644 and directories with mode 755).</para>
83 </listitem>
84 </varlistentry>
85
86 <varlistentry>
87 <term><parameter>LFS=/mnt/lfs</parameter></term>
88 <listitem>
89 <para>The <envar>LFS</envar> variable should be set to the chosen mount
90 point.</para>
91 </listitem>
92 </varlistentry>
93
94 <varlistentry>
95 <term><parameter>LC_ALL=POSIX</parameter></term>
96 <listitem>
97 <para>The <envar>LC_ALL</envar> variable controls the localization of certain
98 programs, making their messages follow the conventions of a specified country.
99 Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
100 (the two are equivalent) ensures that everything will work as expected in
101 the chroot environment.</para>
102 </listitem>
103 </varlistentry>
104
105 <varlistentry>
106 <term><parameter>LFS_TGT=<replaceable>x86_64</replaceable>-lfs-linux-gnu</parameter></term>
107 <listitem>
108 <para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
109 description for use when building our cross compiler and linker and when cross
110 compiling our temporary toolchain. More information is contained in
111 <xref linkend="ch-tools-toolchaintechnotes" role=""/>.
112 If you are not building for 64-bit x86, replace
113 <replaceable>x86_64</replaceable> with some value suitable for your target
114 machine, for example <literal>i686</literal> for 32-bit x86.</para>
115 </listitem>
116 </varlistentry>
117
118 <varlistentry>
119 <term><parameter>PATH=/usr/bin</parameter></term>
120 <listitem>
121 <para>Many modern linux distributions have merged <filename
122 class="directory">/bin</filename> and <filename
123 class="directory">/usr/bin</filename>. When this is the case, the standard
124 <envar>PATH</envar> variable needs just to be set to <filename
125 class="directory">/usr/bin/</filename> for the <xref
126 linkend="chapter-temporary-tools"/> environment. When this is not the
127 case, the following line adds <filename class="directory">/bin</filename>
128 to the path.</para>
129 </listitem>
130 </varlistentry>
131
132 <varlistentry>
133 <term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
134 <listitem>
135 <para>If <filename class="directory">/bin</filename> is not a symbolic
136 link, then it has to be added to the <envar>PATH</envar> variable.</para>
137 </listitem>
138 </varlistentry>
139
140 <varlistentry>
141 <term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
142 <listitem>
143 <para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
144 standard <envar>PATH</envar>, the cross-compiler installed at the beginning
145 of <xref linkend="chapter-cross-tools"/> is picked up by the shell
146 immediately after its installation. This, combined with turning off hashing,
147 limits the risk that the compiler from the host be used instead of the
148 cross-compiler.</para>
149 </listitem>
150 </varlistentry>
151
152 <varlistentry>
153 <term><parameter>CONFIG_SITE=$LFS/usr/share/config.site</parameter></term>
154 <listitem>
155 <para>In <xref linkend="chapter-cross-tools"/> and
156 <xref linkend="chapter-temporary-tools"/>, if this variable is not set,
157 <command>configure</command> scripts
158 may attempt to load configuration items specific to some distributions from
159 <filename>/usr/share/config.site</filename> on the host system. Override
160 it to prevent potential contamination from the host.</para>
161 </listitem>
162 </varlistentry>
163
164 <varlistentry>
165 <term><parameter>export ...</parameter></term>
166 <listitem>
167 <para>While the above commands have set some variables, in order
168 to make them visible within any sub-shells, we export them.</para>
169 </listitem>
170 </varlistentry>
171
172 </variablelist>
173
174 <important>
175
176 <para>Several commercial distributions add a non-documented instantiation
177 of <filename>/etc/bash.bashrc</filename> to the initialization of
178 <command>bash</command>. This file has the potential to modify the
179 <systemitem class="username">lfs</systemitem>
180 user's environment in ways that can affect the building of critical LFS
181 packages. To make sure the <systemitem class="username">lfs</systemitem>
182 user's environment is clean, check for the
183 presence of <filename>/etc/bash.bashrc</filename> and, if present, move it
184 out of the way. As the <systemitem class="username">root</systemitem>
185 user, run:</para>
186
187 <screen role="nodump"><userinput>[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
188
189 <para>After use of the <systemitem class="username">lfs</systemitem>
190 user is finished at the beginning of <xref
191 linkend="chapter-chroot-temporary-tools"/>, you can restore
192 <filename>/etc/bash.bashrc</filename> (if desired).</para>
193
194 <para>Note that the LFS Bash package we will build in
195 <xref linkend="ch-system-bash"/> is not configured to load or execute
196 <filename>/etc/bash.bashrc</filename>, so this file is useless on a
197 completed LFS system.</para>
198 </important>
199
200 <para>Finally, to have the environment fully prepared for building the
201 temporary tools, source the just-created user profile:</para>
202
203<screen><userinput>source ~/.bash_profile</userinput></screen>
204
205</sect1>
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