lfs-book-zh_CN/chapter04/aboutlfs.xml

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<sect1 id="prepare-aboutlfs">
  <?dbhtml filename="aboutlfs.html"?>

  <title>About $LFS</title>

  <para>Throughout this book, the environment variable <envar>LFS</envar> will
  be used. It is paramount that this variable is always defined.
  It should be set to the mount point chosen for the LFS partition.
  Check that the <envar>LFS</envar> variable is set up properly with:</para>

<screen role="nodump"><userinput>echo $LFS</userinput></screen>

  <para>Make sure the output shows the path to the LFS partition's mount
  point, which is <filename class="directory">/mnt/lfs</filename> if the
  provided example was followed. If the output is incorrect, the
  variable can be set with:</para>

<screen role="nodump"><userinput>export LFS=/mnt/lfs</userinput></screen>

  <para>Having this variable set is beneficial in that commands such as
  <command>mkdir $LFS/tools</command> can be typed literally. The shell
  will automatically replace <quote>$LFS</quote> with
  <quote>/mnt/lfs</quote> (or whatever the variable was set to) when it
  processes the command line.</para>

  <para>Do not forget to check that <envar>$LFS</envar> is set whenever
  you leave and reenter the current working environment (as when doing a
  <command>su</command> to <systemitem class="username">root</systemitem>
  or another user).</para>

</sect1>