Writing Apache Modules with Perl and C

2.7. Troubleshooting Modules

Not every module will work the way you think it will the first time you try it. Because the modules written with the Apache API are by definition embedded in the server, debugging them is not as straightforward as debugging a standalone CGI script. In this section, we cover some general module debugging techniques. You'll find more tips later when we discuss specific issues.

2.7.1. C-Level Debugging

If you are using the C API, you can use standard debuggers to step through your module, examine and change data structures, set watch points, and so forth. Be sure to use a version of httpd that has been compiled with debugging symbols and to turn compiler optimizations off. On Unix systems, you can do this by setting the CFLAGS environment variable before running the configure script:

% CFLAGS=-g ./configure ...

Launch your favorite debugger, such as gdb, and run httpd within it. Be sure to launch httpd with the -X flag. Ordinarily, Unix versions of httpd will prefork many independent processes. This forking will confuse the debugger and will probably confuse you too. -X prevents Apache from preforking and keeps the server in the foreground as well. You will also probably want to specify an alternate configuration file with the -f switch so that you can use a high numbered port instead of the default port 80. Be sure to specify different ErrorLog, TransferLog, PidFile, and ScoreBoardFile directives in the alternate configuration file to avoid ...