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

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or more technically 'compiled to run as' – Simon Nov 24 '09 at 23:54
up vote 34 down vote accepted

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:

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

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This answer is wrong. See my answer. – Chris Johnson Feb 11 '14 at 19:27
Hm, on Ubuntu I have neither worker nor prefork listed when I do this... – mlissner Nov 16 '15 at 23:31
On Ubuntu you can use apache2ctl -M to list active modules. – SteffenNielsen Jan 6 at 14:22

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 by the other answers only tells what the default MPM is (based on compiled-in modules), not if that default or another choice is being used at the present time.

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 (e.g. /etc/sysconfig/httpd on CentOS / RedHat)
  2. Add or uncomment this line: HTTPD=/usr/sbin/httpd.worker
  3. Restart Apache

Which MPM is actually 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 actually in use

There are answers on many, many 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.

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FYI, according to the MPM can be a static module on all platforms, or built as a DSO (on Unix). When it is built as a static module, "The server must be rebuilt in order to change the MPM." Is the apache documentation incorrect about the static module MPM being unchangeable except by rebuilding the server? – Steven T. Snyder Feb 12 '14 at 21:34
This sounds very much like something distro specific, with a higher level wrapper around? – andol Mar 7 '14 at 9:08
On CentOS 6.6 /usr/sbin/httpd, /usr/sbin/httpd.event and /usr/sbin/httpd.worker are all distinct binaries with different MPM configured at compile time (prefork, event and worker respectively). Changing the setting of HTTPD in /etc/sysconfig/httpd just controls which binary is run by the init script. – Paul Haldane Nov 28 '14 at 15:59

In Ubuntu 14.04

a2query -M

Tells event, prefork, worker

You can change it by adding symbolic links for mpm_<chosen> from mods-available to mods-enabled in /etc/apache2.

Only one is allowed in a time.

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This needs to be the accepted answer. – Technik Empire Jan 19 at 16:03

On RedHat and derivates, just launch top or ps aux and look at the httpd process name:

  • httpd means Apache is running as prefork
  • httpd.worker means it is running as worker
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Chris Johnson is correct. Go to httpd.conf => add this line:

<Location /server-info>
SetHandler server-info

Restart apache: /etc/init.d/httpd restart. Then access localhost/server-info by your browser and look at MPM Name section.

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Of even nicer, put that between <IfModule info_module> </IfModule> – Lexib0y Oct 25 '15 at 23:57

The answer from Chris Johnson is right.

After enabling the info module, as documented in the Apache Documentation (, this one liner will give you the MPM you're using:

links -dump http://localhost/server-info/?server | grep "MPM Name"
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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.

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This answer is wrong. See my answer. – Chris Johnson Feb 11 '14 at 19:27
@ChrisJohnson, interesting discovery... My understanding was that the MPM could not be changed by configuration, only by compilation. It seems the OP thought the same, since he commented on his question with "or more technically 'compiled to run as'". I'll look into reproducing your answer and once I've confirmed it I'll revoke mine. – Steven T. Snyder Feb 12 '14 at 21:30
I confirmed via the apache documentation at that MPMs can be built as DSO modules and dynamically loaded with the LoadModule directive, on "Unix and similar platforms". So the MPM can indeed be changed at load time under certain circumstances (which might be the most common configuration these days..) – Steven T. Snyder Feb 12 '14 at 21:37

Here's another method that I expect should be reliable in determine which MPM is in use. Add the following to your httpd.conf:

<IfModule prefork.c>
    Header append X-MPM prefork
<IfModule worker.c>
    Header append X-MPM worker

Then check the headers using curl -I localhost | grep X-MPM.

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