In this example, the mod_ibm_ssl.so module cannot be loaded.

httpd: Syntax error on line 198 of /opt/IHS/conf/httpd.conf: Cannot load modules/mod_ibm_ssl.so into server: /opt/IHS/modules/mod_ibm_ssl.so: undefined symbol: ihs_socket_iol_push

Determine the ServerRoot.

~]$ grep ^ServerRoot /opt/IHS/conf/httpd.conf
ServerRoot /opt/IHS

Ensure the httpd.conf file contains the LoadModule directive.

~]$ grep mod_ibm_ssl.so /opt/IHS/conf/httpd.conf
LoadModule ibm_ssl_module modules/mod_ibm_ssl.so

If the module is a relative path, such as modules/mod_ibm_ssl.so, ensure the combination of ServerRoot followed by module correlates to the absolute location of the actual module file. Ensure the module exists.

~]$ ll /opt/IHS/modules/mod_ibm_ssl.so
-rwxrwxr-x. 1 root root 242921 Sep 24  2018 /opt/IHS/modules/mod_ibm_ssl.so

Use the apachectl command or httpd command to display the loaded modules.