All of the commercial Unix operating systems were closed source.

The first open Unix-like is 386BSD which predates Linux. It was said that if 386BSD didn't get mired in a lawsuit, Torvalds would have used it and Linux would not exist.

And the reason BSD survived is the maligned ‘advertising clause’ that most later BSD-type licenses dropped. Berkeley countersued that AT&T had promoted that System V included vi, without the required attribution.