Out of the box Ubuntu user session length

Cannot figure how to change it.

[henry0]

I installed Ubuntu on a machine mostly to use PHP, MySQL and Eclipse, as usually it all works fine,
but, if you do not use the machine even for a short time you need to again enter your password.
This goes on too many times a day.

Do you know how to lengthen to logged in user's session?
thanks

[henry0]

Forget it, found it!
for later reference:
It was the screen saver and power management that logged me out after 10 min.