Chapter 1. What is TUX?

TUX is a kernel-based web server licensed under the GNU General Public License (GPL).

It is currently limited to serving static web pages and coordinating with kernel-space modules, user-space modules, and regular user-space web server daemons to provide dynamic content. Regular user-space web servers do not need to be altered in any way for TUX to coordinate with them. However, user-space code has to use a new interface based on the tux(2) system call.

Although dynamic content is becoming increasingly popular, there is still a need to serve static content. For example, nearly all images are static. TUX can serve static content very efficiently from within the Linux kernel. A similar operation is already performed by the Network File System (NFS) daemon that runs in the kernel.

TUX also has the ability to cache dynamic content. TUX modules (which can be build in kernel space or in user space; user space is recommended) can create "objects" which are stored using the page cache. To respond to a request for dynamic data, a TUX module can send a mix of dynamically-generated data and cached pre-generated objects, taking maximal advantage of TUX's zero-copy architecture.

This new architecture for serving dynamic content requires a new API. The current API's for CGI can not be sufficiently mapped to TUX's API. Thus, existing CGI applications must be converted before TUX will process them. If the CGI application does not require the increased speed of TUX, TUX can process it by running the CGI application normally. This is done through TUX's CGI module. TUX can also handle a complex request (CGI or otherwise) by redirecting it to another web server daemon such as Apache. In other words, static content, TUX modules, old-style CGI applications, and programs specifically written for other webservers can be run on the same system with TUX as the main web server.

In summary, the differences between TUX and other webservers as well as the benefits of using TUX include:

• TUX runs partly within a custom version of kernel 2.4.x or higher and partly as a user-space daemon.

• With a capable network card, TUX enables direct scatter-gather DMA from the page cache directly to the network, thus avoiding data copies.

• Whenever TUX is unsure how to process a request or receives a request it is unable to handle, it always redirects the request to the user-space web server daemon to handle it in an RFC-compliant manner. An example of this user-space web server daemon is Apache.

  Apache is used throughout this document as the user-space web server daemon for readability.

For questions or comments about TUX or this documentation, join the <[email protected]> mailing list. For instructions on joining the mailing list, see http://www.redhat.com/mailing-lists/.

Also visit the Red Hat TUX Web Server product page available at http://www.redhat.com/services/techsupport/application/tux.html.