The fastest way to check your current Apache MPM (Multi-Processing Module) configuration is by running:

apache2ctl -V | grep -i mpm
# Or for httpd:
httpd -V | grep -i mpm

Example output for prefork:

Server MPM:     prefork

For Linux systems using systemd:

systemctl status apache2 | grep -A 5 "Loaded"

Checking loaded modules:

apache2ctl -M | grep mpm_

Primary configuration files to inspect:

# For Debian/Ubuntu:
/etc/apache2/mods-available/mpm_prefork.conf
/etc/apache2/mods-available/mpm_worker.conf

# For CentOS/RHEL:
/etc/httpd/conf.modules.d/00-mpm.conf

Important consideration when switching MPMs:

# Prefork requires:
libapache2-mod-php

# Worker requires:
libapache2-mod-fcgid
php-fpm

Prefork example:

<IfModule mpm_prefork_module>
    StartServers        5
    MinSpareServers     5
    MaxSpareServers     10
    MaxRequestWorkers   150
    MaxConnectionsPerChild 0
</IfModule>

Worker example:

<IfModule mpm_worker_module>
    StartServers        3
    MinSpareThreads     25
    MaxSpareThreads     75 
    ThreadLimit         64
    ThreadsPerChild     25
    MaxRequestWorkers   150
    MaxConnectionsPerChild 0
</IfModule>

If you get conflicting information:

# Verify all enabled modules:
apache2ctl -t -D DUMP_MODULES

# Check for multiple MPM modules loaded:
grep -r "LoadModule mpm_" /etc/apache2/

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The simplest way to check Apache's Multi-Processing Module (MPM) is by running:

apache2ctl -V | grep -i mpm

or for older systems:

httpd -V | grep -i mpm

This will output something like:

Server MPM:     prefork

or

Server MPM:     worker

You can also inspect loaded modules:

apache2ctl -M | grep mpm

This shows which MPM module is currently active in the running Apache instance.

Apache's MPM is configured in these files depending on your OS:

• Debian/Ubuntu: /etc/apache2/mods-available/mpm_*.conf
• CentOS/RHEL: /etc/httpd/conf.modules.d/00-mpm.conf

To check which MPM is enabled:

ls /etc/apache2/mods-enabled/ | grep mpm

For prefork, you'll see multiple httpd processes with single threads:

ps aux | grep httpd

For worker, you'll see fewer parent processes with multiple threads each.

If you're running PHP as an Apache module, check its compatibility:

php -v | grep -i thread

Non-thread-safe (NTS) builds work with prefork, while thread-safe (TS) builds work with worker.

To change MPMs on Debian/Ubuntu:

sudo a2dismod mpm_prefork
sudo a2enmod mpm_worker
sudo systemctl restart apache2

Each MPM has distinct characteristics:

• Prefork: One process per request, more memory usage
• Worker: Threaded model, better for concurrent connections

Choose based on your server's resources and workload requirements.