bash bootup ( user login ) : find boot shell files
           ./etc/profile

   ------------------------------------------------------------
   ./etc/bashrc  //be called at every bootup of new shell. 
                 //define func. & alias, because they would not 
                   be inherited by new shell.
   ------------------------------------------------------------

   skeleton : the default pattern of user directionary 
            ./etc/skel
                .Xdefaults      - X-app boot file
                .bash_logout    |
                .bash_profile   |- set shell configure
                .bashrc         |

            $HOME/.bash_profile
                   - PATH = $PATH:$HOME/bin:$HOME/var:\
                              $HOME/Trimaran/bin
 
            Read-in bash-file to patch shell env :
                   %source .bash_profile
                   or
                   % .     .bash_profile