apache2 Invalid command 'SSLEngine'
On many systems (Ubuntu, Suse, Debian, ...) run the following command to enable Apache's SSL mod:
sudo a2enmod ssl
a2enmod man page
Probably you do not load the ssl module. You should have a LoadModule directive somewhere in your apache configuration files.
Something like:
LoadModule ssl_module /usr/lib64/apache2-prefork/mod_ssl.so
Usually apache configuration template has (on any distribution) a file called (something like) loadmodule.conf
in which you should find a LoadModule
directive for each module you load into apache at server start.
On CentOS 7 installing the package "mod_ssl" and restarting the apache server worked for me:
yum install mod_ssl
systemctl restart httpd