A Private Mac Mercurial Server with SSH Key Authentication

Now, a private Mac Mercurial server with SSH key authentication was set up. I already pushed my main project to the server and updated it at the server side, so repository migration has started without a hitch. But I didn't migrate the subprojects of the main project and some lingering/untended/rogue projects to the server, because they have their own choices of VCSs or none at all: I already smells a trouble, a delicious one. I know there are inter-VCS plugins out there for Mecurial, I'm looking forward using them. So, assuming you have an administrative privilege, here are instructions of how to set up a private SSH Mercurial server.