source: chapter04/settingenviron.xml@ dd61c77

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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 or switched to the &lfs-user; user using a <command>su</command> command
24 with <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. The technique used here achieves the goal of
34 ensuring a clean environment.</para>
36 <para>The new instance of the shell is a <emphasis>non-login</emphasis>
37 shell, which does not read, and execute, the contents of the <filename>/etc/profile</filename> or
38 <filename>.bash_profile</filename> files, but rather reads, and executes, the
39 <filename>.bashrc</filename> file instead. Create the
40 <filename>.bashrc</filename> file now:</para>
42<screen><userinput>cat &gt; ~/.bashrc &lt;&lt; "EOF"
43<literal>set +h
44umask 022
49if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
55 <variablelist>
56 <title>The meaning of the settings in <filename>.bashrc</filename></title>
58 <varlistentry>
59 <term><parameter>set +h</parameter></term>
60 <listitem>
61 <para>The <command>set +h</command> command turns off
62 <command>bash</command>'s hash function. Hashing is ordinarily a useful
63 feature&mdash;<command>bash</command> uses a hash table to remember the
64 full path to executable files to avoid searching the <envar>PATH</envar>
65 time and again to find the same executable. However, the new tools should
66 be used as soon as they are installed. Switching off the hash function forces
67 the shell to search the <envar>PATH</envar> whenever a program is to
68 be run. As such, the shell will find the newly compiled tools in
69 <filename class="directory">$LFS/tools/bin</filename> as soon as they are
70 available without remembering a previous version of the same program
71 provided by the host distro, in
72 <filename class='directory'>/usr/bin</filename> or
73 <filename class='directory'>/bin</filename>.</para>
74 </listitem>
75 </varlistentry>
77 <varlistentry>
78 <term><parameter>umask 022</parameter></term>
79 <listitem>
80 <para>Setting the user file-creation mask (umask) to 022 ensures that newly
81 created files and directories are only writable by their owner, but are
82 readable and executable by anyone (assuming default modes are used by the
83 <function>open(2)</function> system call, new files will end up with permission
84 mode 644 and directories with mode 755).</para>
85 </listitem>
86 </varlistentry>
88 <varlistentry>
89 <term><parameter>LFS=/mnt/lfs</parameter></term>
90 <listitem>
91 <para>The <envar>LFS</envar> variable should be set to the chosen mount
92 point.</para>
93 </listitem>
94 </varlistentry>
96 <varlistentry>
97 <term><parameter>LC_ALL=POSIX</parameter></term>
98 <listitem>
99 <para>The <envar>LC_ALL</envar> variable controls the localization of certain
100 programs, making their messages follow the conventions of a specified country.
101 Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
102 (the two are equivalent) ensures that everything will work as expected in
103 the chroot environment.</para>
104 </listitem>
105 </varlistentry>
107 <varlistentry>
108 <term><parameter>LFS_TGT=<replaceable>x86_64</replaceable>-lfs-linux-gnu</parameter></term>
109 <listitem>
110 <para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
111 description for use when building our cross compiler and linker and when cross
112 compiling our temporary toolchain. More information is contained in
113 <xref linkend="ch-tools-toolchaintechnotes" role=""/>.
114 If you are not building for 64-bit x86, replace
115 <replaceable>x86_64</replaceable> with some value suitable for your target
116 machine, for example <literal>i686</literal> for 32-bit x86.</para>
117 </listitem>
118 </varlistentry>
120 <varlistentry>
121 <term><parameter>PATH=/usr/bin</parameter></term>
122 <listitem>
123 <para>Many modern Linux distributions have merged <filename
124 class="directory">/bin</filename> and <filename
125 class="directory">/usr/bin</filename>. When this is the case, the standard
126 <envar>PATH</envar> variable should be set to <filename
127 class="directory">/usr/bin/</filename> for the <xref
128 linkend="chapter-temporary-tools"/> environment. When this is not the
129 case, the following line adds <filename class="directory">/bin</filename>
130 to the path.</para>
131 </listitem>
132 </varlistentry>
134 <varlistentry>
135 <term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
136 <listitem>
137 <para>If <filename class="directory">/bin</filename> is not a symbolic
138 link, then it has to be added to the <envar>PATH</envar> variable.</para>
139 </listitem>
140 </varlistentry>
142 <varlistentry>
143 <term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
144 <listitem>
145 <para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
146 standard <envar>PATH</envar>, the cross-compiler installed at the beginning
147 of <xref linkend="chapter-cross-tools"/> is picked up by the shell
148 immediately after its installation. This, combined with turning off hashing,
149 limits the risk that the compiler from the host is used instead of the
150 cross-compiler.</para>
151 </listitem>
152 </varlistentry>
154 <varlistentry>
155 <term><parameter>CONFIG_SITE=$LFS/usr/share/</parameter></term>
156 <listitem>
157 <para>In <xref linkend="chapter-cross-tools"/> and
158 <xref linkend="chapter-temporary-tools"/>, if this variable is not set,
159 <command>configure</command> scripts
160 may attempt to load configuration items specific to some distributions from
161 <filename>/usr/share/</filename> on the host system. Override
162 it to prevent potential contamination from the host.</para>
163 </listitem>
164 </varlistentry>
166 <varlistentry>
167 <term><parameter>export ...</parameter></term>
168 <listitem>
169 <para>While the above commands have set some variables, in order
170 to make them visible within any sub-shells, we export them.</para>
171 </listitem>
172 </varlistentry>
174 </variablelist>
176 <important>
178 <para>Several commercial distributions add a non-documented instantiation
179 of <filename>/etc/bash.bashrc</filename> to the initialization of
180 <command>bash</command>. This file has the potential to modify the
181 <systemitem class="username">lfs</systemitem>
182 user's environment in ways that can affect the building of critical LFS
183 packages. To make sure the <systemitem class="username">lfs</systemitem>
184 user's environment is clean, check for the
185 presence of <filename>/etc/bash.bashrc</filename> and, if present, move it
186 out of the way. As the <systemitem class="username">root</systemitem>
187 user, run:</para>
189 <screen role="nodump"><userinput>[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
191 <para>After use of the <systemitem class="username">lfs</systemitem>
192 user is finished at the beginning of <xref
193 linkend="chapter-chroot-temporary-tools"/>, you can restore
194 <filename>/etc/bash.bashrc</filename> (if desired).</para>
196 <para>Note that the LFS Bash package we will build in
197 <xref linkend="ch-system-bash"/> is not configured to load or execute
198 <filename>/etc/bash.bashrc</filename>, so this file is useless on a
199 completed LFS system.</para>
200 </important>
202 <para>Finally, to have the environment fully prepared for building the
203 temporary tools, force the <command>bash</command> shell to read
204 the new user profile:</para>
206<screen><userinput>source ~/.bash_profile</userinput></screen>
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