Once I wanted to see which MPM module is being used and executed the command:
apache2 -V | grep MPM
And got a warning:
[Wed Oct 21 11:36:51.940779 2020] [core:warn] [pid 10054] AH00111: Config variable ${APACHE_RUN_DIR} is not defined
apache2: Syntax error on line 80 of /etc/apache2/apache2.conf: DefaultRuntimeDir must be a valid directory, absolute or relative to ServerRoot
Server MPM:
Apache2 was working at this point and there were no errors.
This warning came up because I ran apache2 instead of the apachectl command.
Therefore, in the future I looked at the name of the module using apachectl:
apachectl -t -D DUMP_MODULES | grep mpm
mpm_event_module (shared)
If you want to make sure that the apache2 configuration is correct, then just run:
apachectl -t
See also my article:
Installing and Configuring Apache2