TUX web server

The TUX web server was a high performance World Wide Web server that could 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.

The TUX project (and kernel patchset) has essentially been deprecated by advances and features that were released with the Linux 2.6 kernel. Patches against a recent kernel source tree to include TUX cause the kernel to not compile cleanly, and advances in other web servers that take advantage of advancements in Linux 2.6 have essentially made the project obsolete.

The TUX mailing list confirms this:

TUX is dead.  There has not been any new development on TUX for about
4 or 5 years, now.  Also, this mailing list is almost dead--I'm only
subscribed because I forgot about it.  Unless you want to write the
updates yourself, TUX will never work on a recent 2.6 Linux kernel.

But TUX is also completely unnecessary, today--the 2.6 kernel can
provide nearly the same static file serving performance as an the 2.4
kernel did with TUX, and the stability is significantly better.  TUX
died because it no longer serves a purpose.

If you want to serve static files very efficiently, and you want to
support large numbers of simultaneous HTTP sessions, then there are
some modern options.  Nginx is the current favorite, I think.

Ryan B. Lynch
ryan b lynch gmail com

(from the TUX mailing list: Re: TUX is dead)

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 security standpoint - see the Controversy 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 but provide functionality for high performance, where a bug does not necessarily give an attacker total control.

Newer web servers do take advantage of improvements in the Linux 2.6 kernel that provide the ability for these web servers to match the performance of an in-kernel webserver despite running outside the kernel, thus largely deprecating TUX.

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