carbon-cache will not start

new installation on Centos7, carbon-cache fails to start (running as root):

 /opt/graphite/bin/carbon-cache.py start
Traceback (most recent call last):
  File "/opt/graphite/bin/carbon-cache.py", line 32, in <module>
    run_twistd_plugin(__file__)
  File "/opt/graphite/lib/carbon/util.py", line 63, in run_twistd_plugin
    from carbon.conf import get_parser
  File "/opt/graphite/lib/carbon/conf.py", line 30, in <module>
    from carbon.database import TimeSeriesDatabase
  File "/opt/graphite/lib/carbon/database.py", line 21, in <module>
    from six import with_metaclass
ImportError: No module named six