Version 6 Unix

Sixth Edition Unix (also known as V6 Unix) was the first version of Unix to see wide release outside Bell Labs. Since source code was available and the license was not explicit enough to forbid it, V6 was taken up as a teaching tool, notably by the University of California at Berkeley and the University of New South Wales. While its influence was somewhat muted by the more successful Version 7 Unix, V6 was the codebase that began the BSD line of Unices.

V6 was also notable for the Lions Book, named after the UNSW professor John Lions who wrote it. This book was an edited selection of the main parts of the kernel as implemented for a Digital PDP-11/40, and was the main source of kernel documentation for many early Unix developers.

The code has been available under a BSD License under agreement from the SCO Group.