mengbiping@mengbiping:~$ sudo apt-get install  ubuntu-desktop
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:
 unity-control-center : Depends: libcheese-gtk23 (>= 3.4.0) but it is not going to be installed
                        Depends: libcheese7 (>= 3.0.1) but it is not going to be installed
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.
mengbiping@mengbiping:~$ sudo apt-get install -f unity-control-center libcheese-gtk23 libcheese7
Reading package lists... Done
Building dependency tree       
Reading state information... Done
libcheese-gtk23 is already the newest version.
libcheese7 is already the newest version.
unity-control-center is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.