shell(1)

        

          shell is a program that takes keyword commdands and passes them to 

the operating system to carry out.when you use GUI,KDE uses konsole and GNOME uses

gnome-terminal.

 

         $ is called a shell prompt and it will appear whenever the shell is ready to accept input.

# means you logged in as the root user or  the terminal emulator that provides superuser privileges.

      

        df: see the current amount of free space on your disk drives.

       free:display the amount fo free memory.