lfs-book-zh_CN/chapter02/aboutlfs.xml

<sect1 id="ch02-aboutlfs">
<title>About $LFS</title>

<para>
Please read the following carefully: throughout this book you will
frequently see the variable name $LFS. $LFS must at all times be
replaced by the directory where the partition that contains the LFS system 
is mounted. How to create and where to mount the partition will be
explaind in full detail later on in chapter 4. In my case the LFS 
partition is mounted  on /mnt/lfs. If I read this book myself and I see 
$LFS somewhere, I will pretend that I read /mnt/lfs. If I read that 
I have to run this command: cp inittab $LFS/etc I actually will run this: 
cp inittab /mnt/lfs/etc
</para>

<para>
It's important that you do this no matter where you read it; be it in
commands you enter on the prompt, or in a file you edit or create.
</para>

<para>
If you want, you can set the environment variable LFS. This way you can
literally enter $LFS instead of replacing it by something like
/mnt/lfs. This is accomplished by running: export LFS=/mnt/lfs
</para>

<para>
If I read cp inittab $LFS/etc, I literally can type cp inittab $LFS/etc
and the shell will replace this command by cp inittab /mnt/lfs/etc
automatically.
</para>

<para>
Do not forget to set the $LFS variable at all times. If you haven't set
the variable and you use it in a command, $LFS will be ignored and whatever
is left will be executed. The command cp inittab $LFS/etc without the $LFS
variable set, will result in copying the inittab file to the /etc
directory which will overwrite your system's inittab. A file like inittab 
isn't that big a problem as it can easily be restored, but if you would 
make this mistake during the installation of the C Library, you can
damage things.
</para>

<para>
One way to make sure that $LFS is set at all times you could add it to
your /root/.bash_profile and/or /root/.bashrc file(s) so everytime you
'su' to user too as to install LFS, the $LFS variable is set for you.
</para>

</sect1>