I checked. It's definitely a fork. Eg, compare https://github.com/NewbiZ/xv6/blob/master/fs/fs.c https://github.com/NewbiZ/xv6/blob/master/fs/fs.c to https://gi

I checked. It's definitely a fork. Eg, compare https://github.com/NewbiZ/xv6/blob/master/fs/fs.c https://github.com/NewbiZ/xv6/blob/master/fs/fs.c to https://github.com/mit-pdos/xv6-public/blob/master/fs.c https://github.com/mit-pdos/xv6-public/blob/master/fs.c . I didn't find a mention of the original copyright.