settingenviron.xml 4.8 KB

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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. <sect1 id="ch-tools-settingenviron">
  8. <?dbhtml filename="settingenvironment.html"?>
  9. <title>Setting Up the Environment</title>
  10. <para>Set up a good working environment by creating two new startup files
  11. for the <command>bash</command> shell. While logged in as user
  12. <systemitem class="username">lfs</systemitem>, issue the following command
  13. to create a new <filename>.bash_profile</filename>:</para>
  14. <screen><userinput>cat &gt; ~/.bash_profile &lt;&lt; "EOF"
  15. <literal>exec env -i HOME=$HOME TERM=$TERM PS1='\u:\w\$ ' /bin/bash</literal>
  16. EOF</userinput></screen>
  17. <para>When logged on as user <systemitem class="username">lfs</systemitem>,
  18. the initial shell is usually a <emphasis>login</emphasis> shell which reads
  19. the <filename>/etc/profile</filename> of the host (probably containing some
  20. settings and environment variables) and then <filename>.bash_profile</filename>.
  21. The <command>exec env -i.../bin/bash</command> command in the
  22. <filename>.bash_profile</filename> file replaces the running shell with a new
  23. one with a completely empty environment, except for the <envar>HOME</envar>,
  24. <envar>TERM</envar>, and <envar>PS1</envar> variables. This ensures that no
  25. unwanted and potentially hazardous environment variables from the host system
  26. leak into the build environment. The technique used here achieves the goal of
  27. ensuring a clean environment.</para>
  28. <para>The new instance of the shell is a <emphasis>non-login</emphasis>
  29. shell, which does not read the <filename>/etc/profile</filename> or
  30. <filename>.bash_profile</filename> files, but rather reads the
  31. <filename>.bashrc</filename> file instead. Create the
  32. <filename>.bashrc</filename> file now:</para>
  33. <screen><userinput>cat &gt; ~/.bashrc &lt;&lt; "EOF"
  34. <literal>set +h
  35. umask 022
  36. LFS=/mnt/lfs
  37. LC_ALL=POSIX
  38. LFS_TGT=$(uname -m)-lfs-linux-gnu
  39. PATH=/tools/bin:/bin:/usr/bin
  40. export LFS LC_ALL LFS_TGT PATH</literal>
  41. EOF</userinput></screen>
  42. <para>The <command>set +h</command> command turns off
  43. <command>bash</command>'s hash function. Hashing is ordinarily a useful
  44. feature&mdash;<command>bash</command> uses a hash table to remember the
  45. full path of executable files to avoid searching the <envar>PATH</envar>
  46. time and again to find the same executable. However, the new tools should
  47. be used as soon as they are installed. By switching off the hash function,
  48. the shell will always search the <envar>PATH</envar> when a program is to
  49. be run. As such, the shell will find the newly compiled tools in
  50. <filename class="directory">$LFS/tools</filename> as soon as they are
  51. available without remembering a previous version of the same program in a
  52. different location.</para>
  53. <para>Setting the user file-creation mask (umask) to 022 ensures that newly
  54. created files and directories are only writable by their owner, but are
  55. readable and executable by anyone (assuming default modes are used by the
  56. <function>open(2)</function> system call, new files will end up with permission
  57. mode 644 and directories with mode 755).</para>
  58. <para>The <envar>LFS</envar> variable should be set to the chosen mount
  59. point.</para>
  60. <para>The <envar>LC_ALL</envar> variable controls the localization of certain
  61. programs, making their messages follow the conventions of a specified country.
  62. If the host system uses a version of Glibc older than 2.2.4, having
  63. <envar>LC_ALL</envar> set to something other than <quote>POSIX</quote> or
  64. <quote>C</quote> (during this chapter) may cause issues if you exit the chroot
  65. environment and wish to return later. Setting <envar>LC_ALL</envar> to
  66. <quote>POSIX</quote> or <quote>C</quote> (the two are equivalent) ensures that
  67. everything will work as expected in the chroot environment.</para>
  68. <para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
  69. description for use when building our cross compiler and linker and when cross
  70. compiling our temporary toolchain. More information is contained in
  71. <xref linkend="ch-tools-toolchaintechnotes" role=""/>.</para>
  72. <para>By putting <filename class="directory">/tools/bin</filename> ahead of the
  73. standard <envar>PATH</envar>, all the programs installed in <xref
  74. linkend="chapter-temporary-tools"/> are picked up by the shell immediately after
  75. their installation. This, combined with turning off hashing, limits the risk
  76. that old programs are used from the host when the same programs are available in
  77. the chapter 5 environment.</para>
  78. <para>Finally, to have the environment fully prepared for building the
  79. temporary tools, source the just-created user profile:</para>
  80. <screen><userinput>source ~/.bash_profile</userinput></screen>
  81. </sect1>