Diffie Hellman parameters slow calculating / multicore

The reasonable solution would be to add the -dsaparam option.

openssl dhparam -dsaparam -out /etc/ssl/private/dhparam.pem 4096

For comparison.

time openssl dhparam -dsaparam -out dhparam.pem 4096
Generating DSA parameters, 4096 bit long prime
+
openssl dhparam -dsaparam -out dhparam.pem 4096  4,42s user 0,15s system 99% cpu 4,574 total

time openssl dhparam -out dhparam.pem 4096
Generating DH parameters, 4096 bit long safe prime, generator 2
This is going to take a long time
+
openssl dhparam -out dhparam.pem 4096  100,27s user 1,60s system 99% cpu 1:41,93 total