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.

Answer 3

The answers given by Series8217 and Andol are both incorrect.

The question was, how to tell if Apache is running prefork or worker. The advice given only tells what the default MPM is (based on compiled-in modules), not if that default or another choice is being used.

If httpd -V shows prefork, that just means prefork is the compiled-in default MPM. That can be overridden by changing an Apache configuration file setting, as shown in this process:

1. Edit the configuration file (/etc/sysconfig/httpd on CentOS / RedHat)
2. Add or uncomment this line: HTTPD=/usr/sbin/httpd.worker
3. Restart Apache

Which MPM is running can be shown using this process:

1. Enable Apache mod_info
2. Query the mod_info url, typically curl localhost/server-info
3. The "Server Settings" section will show "MPM Name: Worker"
4. Run httpd -V again -- it will still show prefork, not worker

Bottom line:

• httpd -V shows the default option, not which option is in use

There are answers on several web sites saying, use httpd -V to tell if Apache is running prefork or worker. They are all wrong. Try the above procedure to see for yourself.