Comment 5 for bug 1096791

On a fresh install as well, if you choose a poor password, it's initially accepted, then warned substantially later that the password is weak (and the install will fail):

Adding users container
Modifying users container
Adding computers container
Modifying computers container
Setting up sam.ldb data
Setting up well known security principals
Setting up sam.ldb users and groups
ERROR(ldb): uncaught exception - 0000052D: Constraint violation - check_password_restrictions: the password does not meet the complexity criteria!
  File "/usr/lib/python2.7/dist-packages/samba/netcmd/__init__.py", line 175, in _run
    return self.run(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/samba/netcmd/domain.py", line 398, in run
    use_rfc2307=use_rfc2307, skip_sysvolacl=False)
  File "/usr/lib/python2.7/dist-packages/samba/provision/__init__.py", line 2058, in provision
    skip_sysvolacl=skip_sysvolacl)
  File "/usr/lib/python2.7/dist-packages/samba/provision/__init__.py", line 1661, in provision_fill
    next_rid=next_rid, dc_rid=dc_rid)
  File "/usr/lib/python2.7/dist-packages/samba/provision/__init__.py", line 1349, in fill_samdb
    "KRBTGTPASS_B64": b64encode(krbtgtpass.encode('utf-16-le'))
  File "/usr/lib/python2.7/dist-packages/samba/provision/common.py", line 50, in setup_add_ldif
    ldb.add_ldif(data, controls)
  File "/usr/lib/python2.7/dist-packages/samba/__init__.py", line 224, in add_ldif
    self.add(msg, controls)
dpkg: error processing samba4 (--configure):
 subprocess installed post-installation script returned error exit status 255
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place
Processing triggers for ureadahead ...
Processing triggers for ufw ...
Errors were encountered while processing:
 samba4
E: Sub-process /usr/bin/dpkg returned an error code (1)