In some situations Apache will fail to start. Running a config test command
will display this error message
AH00526: Syntax error on line 20 of /private/etc/apache2/extra/httpd-mpm.conf: Invalid command 'LockFile', perhaps misspelled or defined by a module not included in the server configuration
In that case, it is safe to delete line 20 from that file. Save your changes and try starting Apache again.