Was there any error message? Does it behave differently if you replace gpu10 with its IP address?

then I add NCCL_DEBUG=INFO and NCCL_DEBUG_SUBSYS=all to see what’s going on, but there is no output file.

It’s possible that init_process_group failed at rendezvous stage (process ip/port discovery using the master as a leader), so that it has not reached NCCL code yet.