Created attachment 10238 [details]
wireshark trace of running the script above to Samba 4.2 master

The following works locally but fails remotely over cifs to Samba 4.2 master (similar to what causes xfstest generic/088 to fail)

#!/usr/bin/env python
#
# Test chmod

import os, grp, pwd, sys

filename = raw_input("Enter a file name to create: ")

uid = pwd.getpwnam("nobody").pw_uid
gid = grp.getgrnam("nogroup").gr_gid
# create a new file with us as owner
fd = os.open(filename, os.O_RDWR | os.O_CREAT)
os.fchown(fd, uid, gid)
os.close(fd)