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 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 Ubuntu 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 custom server kernel. This kernel employs an internal timer frequency of 100Hz instead of the desktop default of 250Hz, uses the deadline I/O scheduler instead of the desktop’s CFQ scheduler, and contains a batch of other minor tweaks for virtualization, memory support, and routing. 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 basic NUMA, a memory design used in some multiprocessor systems that can dramatically increase multiprocessing performance.
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 separate product that truly stands on its own is still a young effort, but one that’s moving along very quickly.
Starting with Ubuntu Server 6.06 LTS, known as Dapper Drake, Ubuntu Server offers officially supported packages for the Red Hat Cluster Suite, Red Hat’s Global File System (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. And there’s a growing lineup of compelling features, including built-in virtualization, interoperability with Windows machines on the network through Samba, automatic version control for configuration files, support for LDAP directory services, hard drive replication over the network, and even a healthy dose of the latest buzzword— cloud computing.
Source of Information : Prentice Hall The official Ubuntu Book 5th Edition 2010
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