The salt-master service on salt master hosts displays these errors on service start / restart:
Jan 01 01:23:45 saltmasterhost.example.com salt-master[12345]: [ERROR ] ReqServer clients tcp://0.0.0.0:4506
Jan 01 01:23:45 saltmasterhost.example.com salt-master[12345]: [ERROR ] ReqServer workers ipc:///var/run/salt/master/workers.ipc
Salt versions before 3007.1
Before salt 3007.1, these messages are logged as ERROR level, however they should be logged as INFO messages.
These are not errors and can be safely ignored.
From salt version 3007.1 onward, they display correctly as INFO messages.