Traceback (most recent call last):
  File "/usr/bin/ubuntu-mate-welcome", line 1131, in _title_changed_cb
    self._do_command(title)
  File "/usr/bin/ubuntu-mate-welcome", line 1252, in _do_command
    subprocess.Popen(['ubiquity','gtk_ui'])
  File "/usr/lib/python3.5/subprocess.py", line 676, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.5/subprocess.py", line 1282, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'ubiquity'