shell - a program that takes keyboard commands and passes them to the operating system to carry out

bash - an acronym for 'Bourne Again SHell，is an enhanced replacement for sh, the original Unix shell program written by Steve Bourne.

3 Terminal -use the program ,we can interact with the shell

4 shell prompt-include your username@machinename ,followed by the current working directory and a dollar sign.

　　　　  　  -if the last character of the prompt is pound sign('#') , the terminal session has superuser  privileges. this means either we are logged in as the root user or we selected emulator that  provides superuser(administrative) privileges.

5 command history - Press the down-arrow key and the previous command disappears.

6 copy-If you highlight some text by holding down the left mouse button and dragging the mouse over it (or double clicking on a word), it is copied into a buffer maintained by X. Pressing the middle mouse button will cause the text to be pasted at the cursor location.

7 a few simple commands

(1)date-displays a calendar of the current time and date

　　   (2)cal-displays a calendar of the current month

(3)df- to see the current amount of free space on your disk drives

(4)free-to display the amount of free memory

(5)exit-clost the terminal emulator window