Apache Cookbook, 2nd Edition

2.10. Why Won’t This Module Work?

Problem

You are trying to install a third-party module, but the Apache Web server refuses to recognize it.

Solution

Consult the sources for the module, or its documentation, or ask the author, in order to determine which version of Apache the package supports.

Discussion

As significant changes are made to the Apache Web server, sometimes compatibility suffers as the API is changed. Although efforts are made to keep this sort of thing to a minimum, sometimes it is unavoidable.

To keep an incompatible module from being loaded and crashing the Web server when used, both modules and the server have a built-in “magic” number that is recorded when they’re built, and that relates to the version of the API. When the server tries to load a module DSO, it compares the module’s magic number with the server’s own, and if they aren’t compatible, the server refuses to load it.

The development team tries to keep the magic number compatibility within major version numbers, but not across them. That is, a module built for Apache 1.3 should work with almost any 1.3 version of the server built after the module was, but it definitely won’t work with a 2.0 server. Contrariwise, a 2.0 module won’t work with a 1.3 server under any circumstances.

See Also

• The Apache Modules Registry at http://modules.apache.org