TUX web server

The TUX web server is a high performance World Wide Web server that can be run partially inside the Linux kernel, in order to serve web pages faster than traditional web servers such as Apache. Its name is derived from the Linux penguin mascot, Tux. It was originally contributed to the Linux kernel project by kernel hacker Ingo Molnar.

Development and Limitations

In its default configuration, TUX is limited to serving only static HTML web pages, meaning that it can't serve web pages that were dynamically created using scripting languages such as PHP or Perl. However, additional modules can be used to work with dynamic scripting languages, similarly to the way Apache uses its mod_php module. These modules can be run from either userspace, meaning they aren't directly in the kernel or from other modules inserted into the kernel. Running modules from userspace is considered much safer from a secuity standpoint - see the Conroversy over Secuity section for a discussion on this.

TUX has never been distributed in the "official" kernel distribution (it is a patchset), although it has has been included with the kernels of some Linux distributions, notably Red Hat, SuSE and Fedora.

It served as a testbed for many features which were integrated separately, including the Native POSIX Thread Library. With the right tuning parameters, the library allows web servers to serve pages at a speed very close to that of a kernelspace web server such as TUX but without its limitations or security concerns.

Architecture and Design Concepts

TUX works basically by "removing a middle step" that is usually required when data is served to the network by a running Unix daemon. Usually data has to be copied from point A to point B to point C. TUX removes the steps needed to get data from a web server's hard drive to the network cable (and client's web browser), and because it runs partially within the kernel but also partially as a daemon, it can serve pages faster than a traditional web server that has to "follow the steps" can.

Controversy over Security

Linux kernel hackers argued that having a daemon, which by design is directly accessible from the Internet (as a web server would have to be), built directly into the kernel is very dangerous. A common bug such as a buffer overflow within TUX could give an attacker full remote superuser control over a machine. They argue that it is much safer to keep such daemons entirely within userspace, where a bug does not necessarily give an attacker total control. However, some Linux distributions, such as Fedora, have added the option to compile TUX into 2.6 kernels.

Related Topics

• Apache Web Server, another web server that runs completely outside of a kernel
• The Linux kernel article, for a general overview of the Linux kernel and architecture

Further Reading

citi-tr-00-8.pdf "The TUX web server: An analysis." Provides an architectural overview of TUX, discusses modifications included in the patch, and how TUX affects kernel operating and performance

ps-redha.pdf "Running TUX Web Server for Linux on Dell Servers." Describes the development process that culminated the release of TUX 2.0.