How do I tell if apache is running as prefork or worker?

Question

How do I tell if apache is running (or configured to run) as prefork or worker?

Answer 1

The MPM is configured at compile time. One way to figure it out afterwards is to list compiled in modules. That list will include the chosen MPM. The listing can be accomplished running the apache binary, with the -l flag.

andreas@halleck:~$ apache2 -l
Compiled in modules:
 core.c
 mod_log_config.c
 mod_logio.c
 worker.c
 http_core.c
 mod_so.c
andreas@halleck:~$

Here we find the module worker.c, hence I'm running the worker MPM.

Answer 2

On RHEL/Fedora/etc, run httpd -V. You will get some output which includes the following:

Server version: Apache/2.2.21 (Unix)
     ...
Architecture:   64-bit
Server MPM:     Prefork
     ...

Here 'Server MPM' is 'Prefork', so my server is running the prefork MPM.