Ssh command to switch boot partitions?

[jofre]

I did something similar, put alpha3 is in ub1 and force on ub2.
It booted on alpha, everything ok, so I switched to force. Set things up and went back to alpha again.
All good, but now, I cannot go back to force.

I do 'setenv ACTIMAGE 2' but it reboots in alpha again

any other way?