Tensorflow Tensorboard default port
You should provide a port flag (--port=6007). 
But I am here to explain how you can find it and other flags without any documentation. Almost all command line tools have a flag -h or --help which shows all possible flags this tool allows.
By running it you will see information about a port flag and that --logdir allows you to 

also pass a comma separated list of log directories

and you can also inspect separate event-files and tags with --event_file and --tag flags
Is there a way to change the default port (6006) on TensorBoard so we could open multiple TensorBoards? Maybe an option like --port="8008"?