1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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3 | "http://www.oasis-open.org/docbook/xml/4.4/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-tools-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 the <filename>/etc/profile</filename> or
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36 | <filename>.bash_profile</filename> files, but rather reads 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 | PATH=/tools/bin:/bin:/usr/bin
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46 | export LFS LC_ALL PATH</literal>
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47 | EOF</userinput></screen>
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48 |
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49 | <para>The <command>set +h</command> command turns off
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50 | <command>bash</command>'s hash function. Hashing is ordinarily a useful
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51 | feature—<command>bash</command> uses a hash table to remember the
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52 | full path of executable files to avoid searching the <envar>PATH</envar>
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53 | time and again to find the same executable. However, the new tools should
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54 | be used as soon as they are installed. By switching off the hash function,
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55 | the shell will always search the <envar>PATH</envar> when a program is to
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56 | be run. As such, the shell will find the newly compiled tools in
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57 | <filename class="directory">$LFS/tools</filename> as soon as they are
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58 | available without remembering a previous version of the same program in a
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59 | different location.</para>
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60 |
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61 | <para>Setting the user file-creation mask (umask) to 022 ensures that newly
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62 | created files and directories are only writable by their owner, but are
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63 | readable and executable by anyone (assuming default modes are used by the
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64 | <function>open(2)</function> system call, new files will end up with permission
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65 | mode 644 and directories with mode 755).</para>
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66 |
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67 | <para>The <envar>LFS</envar> variable should be set to the chosen mount
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68 | point.</para>
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69 |
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70 | <para>The <envar>LC_ALL</envar> variable controls the localization of certain
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71 | programs, making their messages follow the conventions of a specified country.
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72 | If the host system uses a version of Glibc older than 2.2.4, having
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73 | <envar>LC_ALL</envar> set to something other than <quote>POSIX</quote> or
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74 | <quote>C</quote> (during this chapter) may cause issues if you exit the chroot
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75 | environment and wish to return later. Setting <envar>LC_ALL</envar> to
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76 | <quote>POSIX</quote> or <quote>C</quote> (the two are equivalent) ensures that
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77 | everything will work as expected in the chroot environment.</para>
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78 |
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79 | <para>By putting <filename class="directory">/tools/bin</filename> ahead of the
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80 | standard <envar>PATH</envar>, all the programs installed in <xref
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81 | linkend="chapter-temporary-tools"/> are picked up by the shell immediately after
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82 | their installation. This, combined with turning off hashing, limits the risk
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83 | that old programs are used from the host when the same programs are available in
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84 | the chapter 5 environment.</para>
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85 |
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86 | <para>Finally, to have the environment fully prepared for building the
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87 | temporary tools, source the just-created user profile:</para>
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88 |
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89 | <screen><userinput>source ~/.bash_profile</userinput></screen>
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90 |
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91 | </sect1>
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