zengqi@zengqi:~$ 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 (= 1:7.2p2-4)
                  Depends: openssh-sftp-server but it is not going to be installed
                  Recommends: ssh-import-id but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

原因是没有openssh-client啦，只要安装

sudo apt-get install openssh-client=1:7.2p2-4

sudo apt-get install openssh-server

就可以啦