source: chapter04/settingenviron.xml@ a1ad522

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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 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>
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>
40<screen arch="default"><userinput>cat &gt; ~/.bashrc &lt;&lt; "EOF"
41<literal>set +h
42umask 022
45LFS_TGT=$(uname -m)-lfs-linux-gnu
47if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
49export LFS LC_ALL LFS_TGT PATH</literal>
51<screen arch="ml_32,ml_x32,ml_all"><userinput>cat &gt; ~/.bashrc &lt;&lt; "EOF"
52<literal>set +h
53umask 022
60if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
62export LFS LC_ALL LFS_TGT LFS_TGT32 LFS_TGTX32 PATH</literal>
65 <variablelist>
66 <title>The meaning of the settings in <filename>.bashrc</filename></title>
68 <varlistentry>
69 <term><parameter>set +h</parameter></term>
70 <listitem>
71 <para>The <command>set +h</command> command turns off
72 <command>bash</command>'s hash function. Hashing is ordinarily a useful
73 feature&mdash;<command>bash</command> uses a hash table to remember the
74 full path of executable files to avoid searching the <envar>PATH</envar>
75 time and again to find the same executable. However, the new tools should
76 be used as soon as they are installed. By switching off the hash function,
77 the shell will always search the <envar>PATH</envar> when a program is to
78 be run. As such, the shell will find the newly compiled tools in
79 <filename class="directory">$LFS/tools</filename> as soon as they are
80 available without remembering a previous version of the same program in a
81 different location.</para>
82 </listitem>
83 </varlistentry>
85 <varlistentry>
86 <term><parameter>umask 022</parameter></term>
87 <listitem>
88 <para>Setting the user file-creation mask (umask) to 022 ensures that newly
89 created files and directories are only writable by their owner, but are
90 readable and executable by anyone (assuming default modes are used by the
91 <function>open(2)</function> system call, new files will end up with permission
92 mode 644 and directories with mode 755).</para>
93 </listitem>
94 </varlistentry>
96 <varlistentry>
97 <term><parameter>LFS=/mnt/lfs</parameter></term>
98 <listitem>
99 <para>The <envar>LFS</envar> variable should be set to the chosen mount
100 point.</para>
101 </listitem>
102 </varlistentry>
104 <varlistentry>
105 <term><parameter>LC_ALL=POSIX</parameter></term>
106 <listitem>
107 <para>The <envar>LC_ALL</envar> variable controls the localization of certain
108 programs, making their messages follow the conventions of a specified country.
109 Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
110 (the two are equivalent) ensures that everything will work as expected in
111 the chroot environment.</para>
112 </listitem>
113 </varlistentry>
115 <varlistentry>
116 <term><parameter>LFS_TGT=(uname -m)-lfs-linux-gnu</parameter></term>
117 <listitem>
118 <para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
119 description for use when building our cross compiler and linker and when cross
120 compiling our temporary toolchain. More information is contained in
121 <xref linkend="ch-tools-toolchaintechnotes" role=""/>.</para>
122 </listitem>
123 </varlistentry>
125 <varlistentry>
126 <term><parameter>PATH=/usr/bin</parameter></term>
127 <listitem>
128 <para>Many modern linux distributions have merged <filename
129 class="directory">/bin</filename> and <filename
130 class="directory">/usr/bin</filename>. When this is the case, the standard
131 <envar>PATH</envar> variable needs just to be set to <filename
132 class="directory">/usr/bin/</filename> for the <xref
133 linkend="chapter-temporary-tools"/> environment. When this is not the
134 case, the following line adds <filename class="directory">/bin</filename>
135 to the path.</para>
136 </listitem>
137 </varlistentry>
139 <varlistentry>
140 <term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
141 <listitem>
142 <para>If <filename class="directory">/bin</filename> is not a symbolic
143 link, then it has to be added to the <envar>PATH</envar> variable.</para>
144 </listitem>
145 </varlistentry>
147 <varlistentry>
148 <term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
149 <listitem>
150 <para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
151 standard <envar>PATH</envar>, the cross-compiler installed at the beginning
152 of <xref linkend="chapter-cross-tools"/> is picked up by the shell
153 immediately after its installation. This, combined with turning off hashing,
154 limits the risk that the compiler from the host be used instead of the
155 cross-compiler.</para>
156 </listitem>
157 </varlistentry>
159 <varlistentry>
160 <term><parameter>export LFS LC_ALL LFS_TGT PATH</parameter></term>
161 <listitem>
162 <para>While the above commands have set some variables, in order
163 to make them visible within any sub-shells, we export them.</para>
164 </listitem>
165 </varlistentry>
167 </variablelist>
169 <important>
171 <para>Several commercial distributions add a non-documented instantiation
172 of <filename>/etc/bash.bashrc</filename> to the initialization of
173 <command>bash</command>. This file has the potential to modify the
174 <systemitem class="username">lfs</systemitem>
175 user's environment in ways that can affect the building of critical LFS
176 packages. To make sure the <systemitem class="username">lfs</systemitem>
177 user's environment is clean, check for the
178 presence of <filename>/etc/bash.bashrc</filename> and, if present, move it
179 out of the way. As the <systemitem class="username">root</systemitem>
180 user, run:</para>
182 <screen role="nodump"><userinput>[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
184 <para>After use of the <systemitem class="username">lfs</systemitem>
185 user is finished at the beginning of <xref
186 linkend="chapter-chroot-temporary-tools"/>, you can restore
187 <filename>/etc/bash.bashrc</filename> (if desired).</para>
189 <para>Note that the LFS Bash package we will build in
190 <xref linkend="ch-system-bash"/> is not configured to load or execute
191 <filename>/etc/bash.bashrc</filename>, so this file is useless on a
192 completed LFS system.</para>
193 </important>
195 <para>Finally, to have the environment fully prepared for building the
196 temporary tools, source the just-created user profile:</para>
198<screen><userinput>source ~/.bash_profile</userinput></screen>
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