sudo apt-get install openssh-server

Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
openssh-server : Depends: openssh-client (= 1:5.5p1-4ubuntu4) but 1:5.5p1-4ubuntu6 is to be installed
E: Broken packages