不久前我升级到了 Ubuntu 15.04，试用了一些主题。现在我重新安装 Unity 时遇到了问题；
$ sudo apt-get install --reinstall 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:
ubuntu-desktop : Depends: ubuntu-session but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
然后我尝试安装 ubuntu-session 并得到以下回复：
ubuntu-session : Depends: gnome-session-common (= 3.14.0-2ubuntu4) but 3.14.0-2ubuntu5 is to be installed
有什么想法吗？我不确定是否应该强制安装 2ubuntu4 版本。请注意，我必须尝试更新软件包、清理缓存等。