In the event that pw adduser is called without specifying uid or gid and the gid numerically equal to the next uid is already in use, pw will assign the gid 4294967295. If pw adduser is called again and the situation hold for the next uid/gid combination, pw prints 'pw: gid `4294967295' has already been allocated' and exits returning 65.

I hypothesize that internally when pw attempts to create the new gid, something returns -1 as an error instead of returning the next gid. The -1 not tested for and at some point is used to create the group 4294967295. Subsequent uses fail as the gid already exists and that error is properly handled.

Steps to reproduce (assuming the next two uid/gid pairs are free):
# pw addgroup test1
# pw adduser tester1
# pw addgroup test2
# pw adduser tester2
pw: gid `4294967295' has already been allocated
# echo $?
65

First reported on freebsd-questions by Anton Shterenlikht <mexas@bris.ac.uk>

https://lists.freebsd.org/pipermail/freebsd-questions/2015-December/269327.html

Verified in 10.2-RELEASE-p7 by Reporter.