source: chapter04/settingenviron.xml@ 490dc153

11.1 11.1-rc1 11.2 11.2-rc1 arm multilib s6-init trunk xry111/arm64 xry111/clfs-ng xry111/lfs-next xry111/pip3 xry111/queue-11.3 xry111/rust-wip-20221008
Last change on this file since 490dc153 was 490dc153, checked in by Xi Ruoyao <xry111@…>, 10 months ago

remove "+h" in bash commands in chroot (#4998)

In the new cross-compilation approach, the $PATH in chroot does not
contain '/tools/bin'. So "+h" is useless in chroot as the newly
installed tools always replace the temporary counterpart at the same
location.

"+h" in chapter4/settingenviron.xml is kept deliberately. Currently
$LFS/tools/bin only contains programs prefixed with
"x86_64-lfs-linux-gnu-", and it's highly unlikely that any distro will
ever ship a program named with such prefix. So it may seems that we can
remove this "+h" as well. However, the situation may change in future
and we can take this oppertunity to teach the advantage and disvantage
of bash hash feature.

  • Property mode set to 100644
File size: 8.7 KB
Line 
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/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=(uname -m)-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=""/>.</para>
112 </listitem>
113 </varlistentry>
114
115 <varlistentry>
116 <term><parameter>PATH=/usr/bin</parameter></term>
117 <listitem>
118 <para>Many modern linux distributions have merged <filename
119 class="directory">/bin</filename> and <filename
120 class="directory">/usr/bin</filename>. When this is the case, the standard
121 <envar>PATH</envar> variable needs just to be set to <filename
122 class="directory">/usr/bin/</filename> for the <xref
123 linkend="chapter-temporary-tools"/> environment. When this is not the
124 case, the following line adds <filename class="directory">/bin</filename>
125 to the path.</para>
126 </listitem>
127 </varlistentry>
128
129 <varlistentry>
130 <term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
131 <listitem>
132 <para>If <filename class="directory">/bin</filename> is not a symbolic
133 link, then it has to be added to the <envar>PATH</envar> variable.</para>
134 </listitem>
135 </varlistentry>
136
137 <varlistentry>
138 <term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
139 <listitem>
140 <para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
141 standard <envar>PATH</envar>, the cross-compiler installed at the beginning
142 of <xref linkend="chapter-cross-tools"/> is picked up by the shell
143 immediately after its installation. This, combined with turning off hashing,
144 limits the risk that the compiler from the host be used instead of the
145 cross-compiler.</para>
146 </listitem>
147 </varlistentry>
148
149 <varlistentry>
150 <term><parameter>CONFIG_SITE=$LFS/usr/share/config.site</parameter></term>
151 <listitem>
152 <para>In <xref linkend="chapter-cross-tools"/> and
153 <xref linkend="chapter-temporary-tools"/>, if this variable is not set,
154 <command>configure</command> scripts
155 may attempt to load configuration items specific to some distributions from
156 <filename>/usr/share/config.site</filename> on the host system. Override
157 it to prevent potential contamination from the host.</para>
158 </listitem>
159 </varlistentry>
160
161 <varlistentry>
162 <term><parameter>export ...</parameter></term>
163 <listitem>
164 <para>While the above commands have set some variables, in order
165 to make them visible within any sub-shells, we export them.</para>
166 </listitem>
167 </varlistentry>
168
169 </variablelist>
170
171 <important>
172
173 <para>Several commercial distributions add a non-documented instantiation
174 of <filename>/etc/bash.bashrc</filename> to the initialization of
175 <command>bash</command>. This file has the potential to modify the
176 <systemitem class="username">lfs</systemitem>
177 user's environment in ways that can affect the building of critical LFS
178 packages. To make sure the <systemitem class="username">lfs</systemitem>
179 user's environment is clean, check for the
180 presence of <filename>/etc/bash.bashrc</filename> and, if present, move it
181 out of the way. As the <systemitem class="username">root</systemitem>
182 user, run:</para>
183
184 <screen role="nodump"><userinput>[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
185
186 <para>After use of the <systemitem class="username">lfs</systemitem>
187 user is finished at the beginning of <xref
188 linkend="chapter-chroot-temporary-tools"/>, you can restore
189 <filename>/etc/bash.bashrc</filename> (if desired).</para>
190
191 <para>Note that the LFS Bash package we will build in
192 <xref linkend="ch-system-bash"/> is not configured to load or execute
193 <filename>/etc/bash.bashrc</filename>, so this file is useless on a
194 completed LFS system.</para>
195 </important>
196
197 <para>Finally, to have the environment fully prepared for building the
198 temporary tools, source the just-created user profile:</para>
199
200<screen><userinput>source ~/.bash_profile</userinput></screen>
201
202</sect1>
Note: See TracBrowser for help on using the repository browser.