Hi Shun.
First off: we need a bit more information so please do the following:
1. start a terminal session by
either:
a) finding "Terminal" in the Applications menu
ORb) doing
Ctrl+Alt+T i.e. whilst holding down the Ctrl and Alt keys, click the "T" key once and
briefly.
2. in the black window that appears (the Terminal) enter the command
(and press "Enter", of course)
3. copy the resulting text by highlighting it in the usual way then clicking
Ctrl+Shift+C.
4. paste that text into your next post using
Ctrl+V. (Confusing, isn't it?)
5. enter the command
(and Enter)
6. copy the output as before and paste that also into your next post.
All this will help to diagnose your problem.
Keith