I hit the above error when I tried this simple command-
dd if=/dev/random of=dummy bs=1M count=200
This command worked just fine on my fedora 12 VM but wouldn’t on Mac. To my surprise, the problem was in the case of the letter ‘M’. Mac accepts only small letters. Changing ‘M’ to ‘m’ worked!
Mac OS X, is kinda BSD fork. So I expected it to behave just like its other Unix counterparts. But Apple is notorious for doing things its own way! And this quirk is one of them.
Wait, before we close off, just an obvious reminder. Fedora complains of the exact same error when you use lowercase ‘m’. So you need to feed it ‘M’ only.
Hope this saves some 15 minutes of your time.