1. On the machine you want to use to call another machine, say A ->B
We would like A to ssh B without inputing the password.
2. In A machine, type the command:
ssh-keygen -t dsa -b 1024id_dsa.pub email@example.com.X.X:/home/user/.ssh (this might be changed according to different setting)
no key phrases
3. Copy the key to machine B by: scp
4. cat id_dsa.pub >> /path/.ssh/authorizedkeys
5. Now you can ssh B without password from A.
for details I need to read more on security authentication...