I am unable to install openssh-server on an Ubuntu 13.10 virtual machine. Here is the command I used and it's output:
sudo apt-get install openssh-server
[sudo] password for mohamed:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package openssh-server is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'openssh-server' has no installation candidate