Long time, no answer. Did you work it out yourself? Perhaps a bit more detail would evoke an answer.
Googling "linux man genkey" (at the moment I just have access to BSD and Solaris man pages) turns up -- http://linux.die.net/man/1/genkey
, and it looks as though it is an interactive interface to openssl. Don't quote me on that.
When I work with certs, I typically either look at my own notes or refer to this howto -- http://sial.org/howto/openssl/