[19:38 xcpng2 ~]# xe vm-start uuid=[FOO]
The server failed to handle your request, due to an internal error. The given message may give details useful for debugging the problem.
message: xenopsd internal error: Unix.Unix_error(Unix.ENOENT, "open", "/dev/net/tun")

Subsequently, it seems that another VM stopped on its own, and trying to restart that gives the same message. I tried to create a new VM out of curiosity, and that also won't start, with the same message.

Meanwhile there are three existing VMs that are running just fine; two of them are very active and are dealing with a lot of load and network traffic without a problem. I'd prefer not to restart the host, since I don't want to interrupt these VMs just for the hope that a power-cycle will do anything.

How can I evaluate this problem? Searching for this error message hasn't led me to anything useful.