Explained what the sed command is all about

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@588 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter06/shadowpwd-exp.xml

@@ -8,5 +8,11 @@ them manually as those files are used to configure authentication
 details on the system.
 </para>
 
+<para>
+<userinput>sed "s|/var/spool/mail|/var/mail|" login.defs.linux &gt;
+/etc/login.defs</userinput>: /var/spool/mail is the old location of the
+user mailboxes. The location that is used nowadays is /var/mail.
+</para>
+
 </sect2>