What Is Ubuntu Server?

By far the most common reaction from users first encountering Ubuntu Server is one of utter and hopeless confusion. People are foggy on whether Ubuntu Server is a whole new distribution or if it's an Ubuntu derivative like Kubuntu (only for servers) or perhaps something else entirely.

Let's clear things up a bit. The primary software store for Ubuntu and official derivatives is called the Ubuntu archive. The archive is merely a collection of software packages in Debian "deb" format, and it contains every single package that makes up distributions such as Ubuntu, Edubuntu, Xubuntu, Kubuntu, and Ubuntu Server. What makes Kubuntu separate from Ubuntu, then, is only the set of packages from the archive that its installer installs by default and that its CDs carry.

Ubuntu Server is no different. It depends on the very same archive as the standard Ubuntu distribution, but it installs a distinctive set of default packages. Notably, the set of packages comprising Ubuntu Server is very small. The installer will not install things such as a graphical environment or many user programs by default. But since all the packages for Server come from the same official Ubuntu archive, you can install any package you like later. In theory, there's nothing stopping you from transforming an Ubuntu Server install into a regular Ubuntu desktop installation or vice versa (in practice, this is tricky, and we don't recommend you try it). You can even go from running Kubuntu to running Ubuntu Server. The archive paradigm gives you maximum flexibility.

We've established that Ubuntu Server just provides a different set of default packages than Ubuntu. But what's important about that different set? What makes Ubuntu Server a server platform?

The most significant difference is a non-preemptible server kernel with an internal kernel timer frequency of 100 Hz instead of the desktop default of 1 kHz. We'll spare you the OS theory: the idea is to offer some extra performance and throughput for server applications. In addition, the server kernel supports SMP and basic NUMA. SMP, or symmetric multiprocessing, is the code that allows you to utilize more than one processor in your server, and NUMA is a memory design used in some multiprocessor systems that can dramatically increase multiprocessing performance.

Tip: The Big Iron Kernel

In addition to the standard server kernel, Ubuntu Server offers a so-called Big Iron kernel, which is for those very, very few people out there running enormously expensive supercomputing systems. You almost certainly don't want to run the Big Iron kernel. As one Ubuntu developer put it, if you can count the number of processors in your server on your fingers, don't use this kernel. If you ordered your server online by typing a "1" in a "Quantity" box, this is not the kernel for you. If your server didn't require the Occupational Safety and Health Administration to inspect the install location for proper structural support, don't use this kernel. If your BIOS boot sequence takes less than ten minutes and involves fewer than five screens, don't use this kernel. If turning on the server doesn't require a manual and doesn't dim the lights in the entire building, don't use this kernel. If . . . well, you get the idea.

So what else is different in Ubuntu Server? Other than the server kernel and a minimal set of packages, not too much. Though Ubuntu has supported a minimal installation mode for a number of releases, spinning off Ubuntu Server into a proper derivative distribution is still a young effort, and many neat features are planned for the future but aren't available just yet.

Ubuntu Server 6.06 LTS, known as Dapper, does offer officially supported packages for the Red Hat Cluster Suite, Red Hat's Global File System or GFS, Oracle's OCFS2 filesystem, and the Linux Virtual Server utilities: keepalived and ipvsadm. Combined with the specialized server kernel, these bits already let you use your Ubuntu Server for some heavy lifting. Recognizing the wild popularity of the LAMP (Linux, Apache, MySQL, PHP) stack, the Ubuntu Server CD offers a LAMP installation option right at the boot screen. And there's a great lineup of upcoming features: Among other things, we're hoping to throw in a resource manager for cluster folks, automatically place system configuration files under version control, ship with out-of-the-box support for server farm monitoring and hard drive replication over the network, and provide an integrity checker for installed systems directly on Ubuntu CDs.