1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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5 | %general-entities;
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6 | ]>
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7 |
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8 | <sect1 id="ch-preps-settingenviron">
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9 | <?dbhtml filename="settingenvironment.html"?>
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10 |
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11 | <title>Setting Up the Environment</title>
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12 |
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13 | <para>Set up a good working environment by creating two new startup files
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14 | for the <command>bash</command> shell. While logged in as user
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15 | <systemitem class="username">lfs</systemitem>, issue the following command
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16 | to create a new <filename>.bash_profile</filename>:</para>
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17 |
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18 | <screen><userinput>cat > ~/.bash_profile << "EOF"
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19 | <literal>exec env -i HOME=$HOME TERM=$TERM PS1='\u:\w\$ ' /bin/bash</literal>
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20 | EOF</userinput></screen>
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21 |
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22 | <para>When logged on as user <systemitem class="username">lfs</systemitem>,
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23 | the initial shell is usually a <emphasis>login</emphasis> shell which reads
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24 | the <filename>/etc/profile</filename> of the host (probably containing some
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25 | settings and environment variables) and then <filename>.bash_profile</filename>.
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26 | The <command>exec env -i.../bin/bash</command> command in the
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27 | <filename>.bash_profile</filename> file replaces the running shell with a new
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28 | one with a completely empty environment, except for the <envar>HOME</envar>,
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29 | <envar>TERM</envar>, and <envar>PS1</envar> variables. This ensures that no
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30 | unwanted and potentially hazardous environment variables from the host system
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31 | leak into the build environment. The technique used here achieves the goal of
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32 | ensuring a clean environment.</para>
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33 |
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34 | <para>The new instance of the shell is a <emphasis>non-login</emphasis>
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35 | shell, which does not read, and execute, the contents of <filename>/etc/profile</filename> or
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36 | <filename>.bash_profile</filename> files, but rather reads, and executes, the
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37 | <filename>.bashrc</filename> file instead. Create the
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38 | <filename>.bashrc</filename> file now:</para>
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39 |
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40 | <screen><userinput>cat > ~/.bashrc << "EOF"
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41 | <literal>set +h
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42 | umask 022
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43 | LFS=/mnt/lfs
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44 | LC_ALL=POSIX
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45 | LFS_TGT=$(uname -m)-lfs-linux-gnu
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46 | PATH=/usr/bin
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47 | if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
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48 | PATH=$LFS/tools/bin:$PATH
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49 | CONFIG_SITE=$LFS/usr/share/config.site
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50 | export LFS LC_ALL LFS_TGT PATH CONFIG_SITE</literal>
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51 | EOF</userinput></screen>
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52 |
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53 | <variablelist>
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54 | <title>The meaning of the settings in <filename>.bashrc</filename></title>
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55 |
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56 | <varlistentry>
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57 | <term><parameter>set +h</parameter></term>
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58 | <listitem>
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59 | <para>The <command>set +h</command> command turns off
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60 | <command>bash</command>'s hash function. Hashing is ordinarily a useful
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61 | feature—<command>bash</command> uses a hash table to remember the
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62 | full path of executable files to avoid searching the <envar>PATH</envar>
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63 | time and again to find the same executable. However, the new tools should
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64 | be used as soon as they are installed. By switching off the hash function,
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65 | the shell will always search the <envar>PATH</envar> when a program is to
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66 | be run. As such, the shell will find the newly compiled tools in
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67 | <filename class="directory">$LFS/tools</filename> as soon as they are
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68 | available without remembering a previous version of the same program in a
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69 | different location.</para>
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70 | </listitem>
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71 | </varlistentry>
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72 |
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73 | <varlistentry>
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74 | <term><parameter>umask 022</parameter></term>
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75 | <listitem>
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76 | <para>Setting the user file-creation mask (umask) to 022 ensures that newly
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77 | created files and directories are only writable by their owner, but are
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78 | readable and executable by anyone (assuming default modes are used by the
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79 | <function>open(2)</function> system call, new files will end up with permission
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80 | mode 644 and directories with mode 755).</para>
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81 | </listitem>
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82 | </varlistentry>
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83 |
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84 | <varlistentry>
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85 | <term><parameter>LFS=/mnt/lfs</parameter></term>
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86 | <listitem>
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87 | <para>The <envar>LFS</envar> variable should be set to the chosen mount
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88 | point.</para>
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89 | </listitem>
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90 | </varlistentry>
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91 |
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92 | <varlistentry>
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93 | <term><parameter>LC_ALL=POSIX</parameter></term>
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94 | <listitem>
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95 | <para>The <envar>LC_ALL</envar> variable controls the localization of certain
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96 | programs, making their messages follow the conventions of a specified country.
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97 | Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
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98 | (the two are equivalent) ensures that everything will work as expected in
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99 | the chroot environment.</para>
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100 | </listitem>
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101 | </varlistentry>
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102 |
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103 | <varlistentry>
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104 | <term><parameter>LFS_TGT=(uname -m)-lfs-linux-gnu</parameter></term>
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105 | <listitem>
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106 | <para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
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107 | description for use when building our cross compiler and linker and when cross
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108 | compiling our temporary toolchain. More information is contained in
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109 | <xref linkend="ch-tools-toolchaintechnotes" role=""/>.</para>
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110 | </listitem>
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111 | </varlistentry>
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112 |
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113 | <varlistentry>
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114 | <term><parameter>PATH=/usr/bin</parameter></term>
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115 | <listitem>
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116 | <para>Many modern linux distributions have merged <filename
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117 | class="directory">/bin</filename> and <filename
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118 | class="directory">/usr/bin</filename>. When this is the case, the standard
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119 | <envar>PATH</envar> variable needs just to be set to <filename
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120 | class="directory">/usr/bin/</filename> for the <xref
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121 | linkend="chapter-temporary-tools"/> environment. When this is not the
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122 | case, the following line adds <filename class="directory">/bin</filename>
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123 | to the path.</para>
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124 | </listitem>
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125 | </varlistentry>
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126 |
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127 | <varlistentry>
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128 | <term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
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129 | <listitem>
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130 | <para>If <filename class="directory">/bin</filename> is not a symbolic
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131 | link, then it has to be added to the <envar>PATH</envar> variable.</para>
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132 | </listitem>
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133 | </varlistentry>
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134 |
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135 | <varlistentry>
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136 | <term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
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137 | <listitem>
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138 | <para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
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139 | standard <envar>PATH</envar>, the cross-compiler installed at the beginning
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140 | of <xref linkend="chapter-cross-tools"/> is picked up by the shell
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141 | immediately after its installation. This, combined with turning off hashing,
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142 | limits the risk that the compiler from the host be used instead of the
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143 | cross-compiler.</para>
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144 | </listitem>
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145 | </varlistentry>
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146 |
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147 | <varlistentry>
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148 | <term><parameter>CONFIG_SITE=$LFS/usr/share/config.site</parameter></term>
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149 | <listitem>
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150 | <para>In <xref linkend="chapter-cross-tools"/> and
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151 | <xref linkend="chapter-temporary-tools"/>, if this variable is not set,
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152 | <command>configure</command> scripts
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153 | may attempt to load configuration items specific to some distributions from
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154 | <filename>/usr/share/config.site</filename> on the host system. Override
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155 | it to prevent potential contamination from the host.</para>
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156 | </listitem>
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157 | </varlistentry>
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158 |
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159 | <varlistentry>
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160 | <term><parameter>export ...</parameter></term>
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161 | <listitem>
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162 | <para>While the above commands have set some variables, in order
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163 | to make them visible within any sub-shells, we export them.</para>
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164 | </listitem>
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165 | </varlistentry>
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166 |
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167 | </variablelist>
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168 |
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169 | <important>
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170 |
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171 | <para>Several commercial distributions add a non-documented instantiation
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172 | of <filename>/etc/bash.bashrc</filename> to the initialization of
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173 | <command>bash</command>. This file has the potential to modify the
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174 | <systemitem class="username">lfs</systemitem>
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175 | user's environment in ways that can affect the building of critical LFS
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176 | packages. To make sure the <systemitem class="username">lfs</systemitem>
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177 | user's environment is clean, check for the
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178 | presence of <filename>/etc/bash.bashrc</filename> and, if present, move it
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179 | out of the way. As the <systemitem class="username">root</systemitem>
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180 | user, run:</para>
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181 |
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182 | <screen role="nodump"><userinput>[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
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183 |
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184 | <para>After use of the <systemitem class="username">lfs</systemitem>
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185 | user is finished at the beginning of <xref
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186 | linkend="chapter-chroot-temporary-tools"/>, you can restore
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187 | <filename>/etc/bash.bashrc</filename> (if desired).</para>
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188 |
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189 | <para>Note that the LFS Bash package we will build in
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190 | <xref linkend="ch-system-bash"/> is not configured to load or execute
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191 | <filename>/etc/bash.bashrc</filename>, so this file is useless on a
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192 | completed LFS system.</para>
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193 | </important>
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194 |
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195 | <para>Finally, to have the environment fully prepared for building the
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196 | temporary tools, source the just-created user profile:</para>
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197 |
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198 | <screen><userinput>source ~/.bash_profile</userinput></screen>
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199 |
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200 | </sect1>
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