Starting Apache as service quits with SIGWINCH

When running service apache start I see in the log file this entry: [mpm_event:notice] [pid 1906:tid XXX] AH00489: Apache/2.4.23 (Unix) OpenSSL/1.0.2g PHP/7.0.9 configured -- resuming normal operations [core:notice] [pid 1906:tid XXX] AH00094: Command line: '/usr/sbin/httpd' [mpm_event:notice] [pid 1906:tid XXX] AH00492: caught SIGWINCH, shutting down gracefully and the service apache does not start? I can find in internet what SIGWINCH means [Window size change] but it does not really help me in this case. The file /etc/systemd/system/apache.service: [Unit] Description=The Apache Webserver [FaF Compiled] After=network.target nss-lookup.target time-sync.target Before=getty@tty1.service plymouth-quit.service xdm.service [Service] Type=notify PrivateTmp=true ExecStart=/usr/sbin/httpd -k start ExecReload=/usr/sbin/httpd -k graceful ExecStop=/usr/sbin/httpd -k graceful-stop KillMode=mixed [Install] WantedBy=multi-user.target Alias=httpd.service apache.service Running on SLES 12 SP1. I have compiled Apache on my own. Starting it with apachectl -k start works perfectly and I can access and run the PHP code. **My question:** What am I doing wrong that the apache service does not start. I have enabled it with systemctl enable apache. This was the output: ln -s '/usr/lib/systemd/system/apache2.service' '/etc/systemd/system/httpd.service' ln -s '/usr/lib/systemd/system/apache2.service' '/etc/systemd/system/apache.service' ln -s '/usr/lib/systemd/system/apache2.service' '/etc/systemd/system/multi-user.target.wants/apache2.service'