One of the basic principles of computer security is never to run anything you don't need.
pgrepping for a process today when I noticed that my Ubuntu 9.04 (desktop) machine was running a git server daemon. After a quick swear, I discovered that the
git-daemon-run package had been (probably inadvertently) installed, and removing it got rid of that process (and ensured that it wouldn't be restarted later).
But in other cases, I want the server package to be installed, but don't want the server daemon running. For example, I use
lighttpd for internal testing (it's started by specific test scripts for some applications, and listens only on localhost in those configurations) but I don't want it listening for outside connections with some random config file. (If I wanted to run one listening for outside connections, I'd configure and run it myself.)
I really don't like running all sorts of random servers I don't need on Internet-exposed machines, since who knows what security holes they open up. And I prefer not to have to muck about with firewalls, since that's yet another potential source of errors and misconfigurations that can open up security holes. It's not so hard to have Unix machines configured not to start any servers unless specifically asked to do so by the admin; NetBSD (and OpenBSD, too, I think) come this way by default.
How do I configure my Ubuntu systems never to start any kind of server daemon unless I specifically tell it I want it started?
(Asking to have a package installed is not, in my book, asking to start a server. If it is supposed to be, it's a terrible user interface, since many package installs don't even have a server to start, so it makes it far too easy to inadvertently start a server without realizing you've done so.)
EDIT: Just to make it clear, the problem is not that I want to be able to stop existing servers. The problem is that I don't want new servers started without an explicit request. This means I should be able to do any sysadmin task, such as installing a package, and be confident that no servers have started. Most responses do not address this point.