Ubuntu - speakers not muted when inserting earphone jack - SOLUTION

I recently installed ubuntu 10.04 on a laptop, and found that the built-in speakers are not muted when inserting the earphone jack. After I googled a bit, I found the solution:

run alsamixer
use the left and right arrow keys to move between items, look for the Headphone Jack Sense item, it should say [Off] at the end, and MM in the box.
Press m to change it to 00.

From now on the built-in speakers should be muted when inserting the earphone jack.