Fixing "Error from osm_opensm_bind (0x2B) Perhaps another instance of OpenSM is already running"

Sometimes, OpenSM service won't start automatically or restart  it will fail:

OpenSM 3.3.11 UMAD 

Entering DISCOVERING state 


Error from osm_opensm_bind (0x2B)
Perhaps another instance of OpenSM is already running
Exiting SM 

First thing we want to confirm is that the card currently in IB mode:
Then, opensm.conf has to be adjusted. By default its first option, GUID, is empty. Take GUID of an active port (port 1 or port 2, 0x0002c903000232db in the example) and replace the following line: Done, service should start as expected.