how to enable sshd in imac

Apart from turning on Remote Login, you don't have to do anything. It's just SSH; it's not sshd.

 

SSHD = Solid State Hard drive (hardware)
SSH = Secure Shell (software)

I think the OP just got a little confused. But as csj stated, there is only SSH.

 

No, sshd is the SSH daemon, the server software for SSH. SSHD has also been used recently by Seagate for their solid state hybrid drives (hard drives with some flash on board for performance benefits), although it's not necessarily a widespread term. The proper nomenclature for a pure solid state drive is SSD, not SSHD.

In regards to the OP's question, turning on the Remote Login preference is all that's required to enable SSH on a Mac. The SSH daemon doesn't run all the time, it's launched on-demand by the launchd system. Just because there's no sshd process doesn't mean that you can't SSH into your system.

If you're having problems with SSH access, it's not necessarily because there's no sshd process. You should probably post elsewhere (like the OS X forum), as it's not really an iMac-specific problem.