source: chapter04/settingenviron.xml@ 2d66549

ml-11.0 multilib
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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 arch="default"><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
49CONFIG_SITE=$LFS/usr/share/config.site
50export LFS LC_ALL LFS_TGT PATH CONFIG_SITE</literal>
51EOF</userinput></screen>
52<screen arch="ml_32,ml_x32,ml_all"><userinput>cat &gt; ~/.bashrc &lt;&lt; "EOF"
53<literal>set +h
54umask 022
55LFS=/mnt/lfs
56LC_ALL=POSIX
57LFS_TGT=x86_64-lfs-linux-gnu
58LFS_TGT32=i686-lfs-linux-gnu
59LFS_TGTX32=x86_64-lfs-linux-gnux32
60PATH=/usr/bin
61if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
62PATH=$LFS/tools/bin:$PATH
63export LFS LC_ALL LFS_TGT LFS_TGT32 LFS_TGTX32 PATH</literal>
64EOF</userinput></screen>
65
66 <variablelist>
67 <title>The meaning of the settings in <filename>.bashrc</filename></title>
68
69 <varlistentry>
70 <term><parameter>set +h</parameter></term>
71 <listitem>
72 <para>The <command>set +h</command> command turns off
73 <command>bash</command>'s hash function. Hashing is ordinarily a useful
74 feature&mdash;<command>bash</command> uses a hash table to remember the
75 full path of executable files to avoid searching the <envar>PATH</envar>
76 time and again to find the same executable. However, the new tools should
77 be used as soon as they are installed. By switching off the hash function,
78 the shell will always search the <envar>PATH</envar> when a program is to
79 be run. As such, the shell will find the newly compiled tools in
80 <filename class="directory">$LFS/tools</filename> as soon as they are
81 available without remembering a previous version of the same program in a
82 different location.</para>
83 </listitem>
84 </varlistentry>
85
86 <varlistentry>
87 <term><parameter>umask 022</parameter></term>
88 <listitem>
89 <para>Setting the user file-creation mask (umask) to 022 ensures that newly
90 created files and directories are only writable by their owner, but are
91 readable and executable by anyone (assuming default modes are used by the
92 <function>open(2)</function> system call, new files will end up with permission
93 mode 644 and directories with mode 755).</para>
94 </listitem>
95 </varlistentry>
96
97 <varlistentry>
98 <term><parameter>LFS=/mnt/lfs</parameter></term>
99 <listitem>
100 <para>The <envar>LFS</envar> variable should be set to the chosen mount
101 point.</para>
102 </listitem>
103 </varlistentry>
104
105 <varlistentry>
106 <term><parameter>LC_ALL=POSIX</parameter></term>
107 <listitem>
108 <para>The <envar>LC_ALL</envar> variable controls the localization of certain
109 programs, making their messages follow the conventions of a specified country.
110 Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
111 (the two are equivalent) ensures that everything will work as expected in
112 the chroot environment.</para>
113 </listitem>
114 </varlistentry>
115
116 <varlistentry>
117 <term><parameter>LFS_TGT=(uname -m)-lfs-linux-gnu</parameter></term>
118 <listitem>
119 <para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
120 description for use when building our cross compiler and linker and when cross
121 compiling our temporary toolchain. More information is contained in
122 <xref linkend="ch-tools-toolchaintechnotes" role=""/>.</para>
123 </listitem>
124 </varlistentry>
125
126 <varlistentry>
127 <term><parameter>PATH=/usr/bin</parameter></term>
128 <listitem>
129 <para>Many modern linux distributions have merged <filename
130 class="directory">/bin</filename> and <filename
131 class="directory">/usr/bin</filename>. When this is the case, the standard
132 <envar>PATH</envar> variable needs just to be set to <filename
133 class="directory">/usr/bin/</filename> for the <xref
134 linkend="chapter-temporary-tools"/> environment. When this is not the
135 case, the following line adds <filename class="directory">/bin</filename>
136 to the path.</para>
137 </listitem>
138 </varlistentry>
139
140 <varlistentry>
141 <term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
142 <listitem>
143 <para>If <filename class="directory">/bin</filename> is not a symbolic
144 link, then it has to be added to the <envar>PATH</envar> variable.</para>
145 </listitem>
146 </varlistentry>
147
148 <varlistentry>
149 <term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
150 <listitem>
151 <para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
152 standard <envar>PATH</envar>, the cross-compiler installed at the beginning
153 of <xref linkend="chapter-cross-tools"/> is picked up by the shell
154 immediately after its installation. This, combined with turning off hashing,
155 limits the risk that the compiler from the host be used instead of the
156 cross-compiler.</para>
157 </listitem>
158 </varlistentry>
159
160 <varlistentry>
161 <term><parameter>CONFIG_SITE=$LFS/usr/share/config.site</parameter></term>
162 <listitem>
163 <para>In <xref linkend="chapter-cross-tools"/> and
164 <xref linkend="chapter-temporary-tools"/>, if this variable is not set,
165 <command>configure</command> scripts
166 may attempt to load configuration items specific to some distributions from
167 <filename>/usr/share/config.site</filename> on the host system. Override
168 it to prevent potential contamination from the host.</para>
169 </listitem>
170 </varlistentry>
171
172 <varlistentry>
173 <term><parameter>export ...</parameter></term>
174 <listitem>
175 <para>While the above commands have set some variables, in order
176 to make them visible within any sub-shells, we export them.</para>
177 </listitem>
178 </varlistentry>
179
180 </variablelist>
181
182 <important>
183
184 <para>Several commercial distributions add a non-documented instantiation
185 of <filename>/etc/bash.bashrc</filename> to the initialization of
186 <command>bash</command>. This file has the potential to modify the
187 <systemitem class="username">lfs</systemitem>
188 user's environment in ways that can affect the building of critical LFS
189 packages. To make sure the <systemitem class="username">lfs</systemitem>
190 user's environment is clean, check for the
191 presence of <filename>/etc/bash.bashrc</filename> and, if present, move it
192 out of the way. As the <systemitem class="username">root</systemitem>
193 user, run:</para>
194
195 <screen role="nodump"><userinput>[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
196
197 <para>After use of the <systemitem class="username">lfs</systemitem>
198 user is finished at the beginning of <xref
199 linkend="chapter-chroot-temporary-tools"/>, you can restore
200 <filename>/etc/bash.bashrc</filename> (if desired).</para>
201
202 <para>Note that the LFS Bash package we will build in
203 <xref linkend="ch-system-bash"/> is not configured to load or execute
204 <filename>/etc/bash.bashrc</filename>, so this file is useless on a
205 completed LFS system.</para>
206 </important>
207
208 <para>Finally, to have the environment fully prepared for building the
209 temporary tools, source the just-created user profile:</para>
210
211<screen><userinput>source ~/.bash_profile</userinput></screen>
212
213</sect1>
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