What is the difference between Ubuntu and Debian server?

Question

I know Ubuntu is basically Debian, and I know Ubuntu releases every 6 months, Debian every 2 years. However, I want to know more the advanced differences between them. If they have the same base, what is the difference between them?

Answer 1

Some of the differences:

• Debian uses SystemV style init, and inittab;
  Ubuntu uses Upstart
• Debian has root account enabled by default, but can be configured to use sudo;
  Ubuntu uses sudo and has no root account enabled
• Debian has a release cycle not predefined;
  Ubuntu has a release cycle of six months (two years for LTS)
• Debian has a rolling unstable release, called sid;
  Ubuntu has nothing similar
• Debian has a testing release that is destined to become the next stable;
  Ubuntu has a development release, initially based on sid that becomes the stable
• Debian uses gnome2/metacity by default;
  Ubuntu uses gnome2/compiz+unity by default;
  
• Debian is released for several architectures (more than every other distro);
  Ubuntu essentially only for x86, ARM and amd64

this is what comes to my mind, something might be inexact or wrong, and I might have missed something big. I wait to see other answers.

Edit

missed the word "server" in the title:
Debian has not a server version, you get a so called server not installing a desktop environment.

Answer 2

The difference is that there's an ubuntu server but not a debian server.

Ubuntu server comes with a variety of packages predefined by the maintainers, debian let these choices to its administrator.

As far as I Know there's no special patches to the kernel made by canonical to the default kernel.

Answer 3

Like Enzotib mentioned in his answer, Debian uses a SystemV style init, while Ubuntu uses upstart. Since servers aren't restarted very often (or at least they shouldn't be :P), the init system doesn't really matter. That's about where the differences end.

Most of Ubuntu's packages are just recompiled from Debian, so the software defaults (like the Apache web server configuration) are identical. I have two servers, one running Ubuntu Server 11.04 and one running Debian 6.0 and there hasn't been a single instance where I couldn't just copy a configuration file between them and have it work correctly.