Debugging Apache Web Server Problems
The apache web server has become the predominant web server on the Internet for it's scalability, standards compliance and the numerous features that come bundled with the server. As more and more features are added to apache, and as web applications evolve to meet new demands, bugs will periodically surface in applications and the web server code base itself. Since application and server bugs can lead to service failures and downtime, it is important to have a good set of tools to assist with isolating and locating problems. This article provides an introduction to debugging apache web server problems, and covers several tools and techniques that can help troubleshoot problems when they arise.
Isolating problems with apache's single process mode
When debugging web server problems, isolating a problem is the first step in troubleshooting an issue. Since a typical apache installation runs with several processes, and in the case of the worker and event MPMs multiple threads per process, starting apache as a single process can simplify troubleshooting. There are two ways to start apache as a single process. The first method requires editing the number of processes and threads in the apache servers MPM configuration stanza. An alternative method is to use apache's "-X" option to start the server in single process mode:
$ httpd -X
When single process mode is used, apache will not fork new processes or disassociate from the terminal. This ensures that all communications flow through one process, which allows troubleshooting procedures (e.g., attaching to the httpd process with gdb) to be used on a single process instead of multiple processes.
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