Throughout this book, the environment variable LFS 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 LFS variable
        is set up properly with:
      
echo $LFS
        Make sure the output shows the path to the LFS partition's mount
        point, which is /mnt/lfs if the
        provided example was followed. If the output is incorrect, the
        variable can be set with:
      
export LFS=/mnt/lfs
Having this variable set is beneficial in that commands such as mkdir $LFS/tools can be typed literally. The shell will automatically replace “$LFS” with “/mnt/lfs” (or whatever the variable was set to) when it processes the command line.
        Do not forget to check that $LFS is set
        whenever you leave and reenter the current working environment (as
        when doing a su to
        root or another user).