source: chapter04/settingenviron.xml@ df77b24

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Last change on this file since df77b24 was df77b24, checked in by Xi Ruoyao <xry111@…>, 15 months ago

env: set CONFIG_SITE to prevent potential contamination from host distro

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@12045 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

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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=$(uname -m)-lfs-linux-gnu
46PATH=/usr/bin
47if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
48PATH=$LFS/tools/bin:$PATH
49CONFIG_SITE=$LFS/usr/share/config.site
50export LFS LC_ALL LFS_TGT PATH CONFIG_SITE</literal>
51EOF</userinput></screen>
52
53 <variablelist>
54 <title>The meaning of the settings in <filename>.bashrc</filename></title>
55
56 <varlistentry>
57 <term><parameter>set +h</parameter></term>
58 <listitem>
59 <para>The <command>set +h</command> command turns off
60 <command>bash</command>'s hash function. Hashing is ordinarily a useful
61 feature&mdash;<command>bash</command> uses a hash table to remember the
62 full path of executable files to avoid searching the <envar>PATH</envar>
63 time and again to find the same executable. However, the new tools should
64 be used as soon as they are installed. By switching off the hash function,
65 the shell will always search the <envar>PATH</envar> when a program is to
66 be run. As such, the shell will find the newly compiled tools in
67 <filename class="directory">$LFS/tools</filename> as soon as they are
68 available without remembering a previous version of the same program in a
69 different location.</para>
70 </listitem>
71 </varlistentry>
72
73 <varlistentry>
74 <term><parameter>umask 022</parameter></term>
75 <listitem>
76 <para>Setting the user file-creation mask (umask) to 022 ensures that newly
77 created files and directories are only writable by their owner, but are
78 readable and executable by anyone (assuming default modes are used by the
79 <function>open(2)</function> system call, new files will end up with permission
80 mode 644 and directories with mode 755).</para>
81 </listitem>
82 </varlistentry>
83
84 <varlistentry>
85 <term><parameter>LFS=/mnt/lfs</parameter></term>
86 <listitem>
87 <para>The <envar>LFS</envar> variable should be set to the chosen mount
88 point.</para>
89 </listitem>
90 </varlistentry>
91
92 <varlistentry>
93 <term><parameter>LC_ALL=POSIX</parameter></term>
94 <listitem>
95 <para>The <envar>LC_ALL</envar> variable controls the localization of certain
96 programs, making their messages follow the conventions of a specified country.
97 Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
98 (the two are equivalent) ensures that everything will work as expected in
99 the chroot environment.</para>
100 </listitem>
101 </varlistentry>
102
103 <varlistentry>
104 <term><parameter>LFS_TGT=(uname -m)-lfs-linux-gnu</parameter></term>
105 <listitem>
106 <para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
107 description for use when building our cross compiler and linker and when cross
108 compiling our temporary toolchain. More information is contained in
109 <xref linkend="ch-tools-toolchaintechnotes" role=""/>.</para>
110 </listitem>
111 </varlistentry>
112
113 <varlistentry>
114 <term><parameter>PATH=/usr/bin</parameter></term>
115 <listitem>
116 <para>Many modern linux distributions have merged <filename
117 class="directory">/bin</filename> and <filename
118 class="directory">/usr/bin</filename>. When this is the case, the standard
119 <envar>PATH</envar> variable needs just to be set to <filename
120 class="directory">/usr/bin/</filename> for the <xref
121 linkend="chapter-temporary-tools"/> environment. When this is not the
122 case, the following line adds <filename class="directory">/bin</filename>
123 to the path.</para>
124 </listitem>
125 </varlistentry>
126
127 <varlistentry>
128 <term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
129 <listitem>
130 <para>If <filename class="directory">/bin</filename> is not a symbolic
131 link, then it has to be added to the <envar>PATH</envar> variable.</para>
132 </listitem>
133 </varlistentry>
134
135 <varlistentry>
136 <term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
137 <listitem>
138 <para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
139 standard <envar>PATH</envar>, the cross-compiler installed at the beginning
140 of <xref linkend="chapter-cross-tools"/> is picked up by the shell
141 immediately after its installation. This, combined with turning off hashing,
142 limits the risk that the compiler from the host be used instead of the
143 cross-compiler.</para>
144 </listitem>
145 </varlistentry>
146
147 <varlistentry>
148 <term><parameter>CONFIG_SITE=$LFS/usr/share/config.site</parameter></term>
149 <listitem>
150 <para>In <xref linkend="chapter-cross-tools"/> and
151 <xref linkend="chapter-temporary-tools"/>, if this variable is not set,
152 <command>configure</command> scripts
153 will attempt to load configuration from
154 <filename>/usr/share/config.site</filename> of the host system. Override
155 it to prevent potential contamination from host.</para>
156 </listitem>
157 </varlistentry>
158
159 <varlistentry>
160 <term><parameter>export ...</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>
166
167 </variablelist>
168
169 <important>
170
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>
181
182 <screen role="nodump"><userinput>[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
183
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>
188
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>
194
195 <para>Finally, to have the environment fully prepared for building the
196 temporary tools, source the just-created user profile:</para>
197
198<screen><userinput>source ~/.bash_profile</userinput></screen>
199
200</sect1>
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