Can't restart stopped VMs; unclear error message

[the_jest]

I have an XCP-NG 8.3.0 installation, on just a single host, that has been extremely stable for some time, usually running 5–6 VMs. I needed to restart one VM to update some packages, and it shut down cleanly but did not restart. When I tried to do it manually, I got:

[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.

[Danp]

Have you tried restarting the toolstack?

To investigate further, you can review the host's log files https://docs.xcp-ng.org/troubleshooting/log-files/

[the_jest]

@Danp
Yes, I did restart the toolstack; sorry for not saying this. It successfully restarted, but did not resolve the problem. Meanwhile the existing VMs do continue to work.

I also updated all the patches (which I do semi-regularly as well).

I have tried to look at the log files, but there's nothing obvious there that makes sense to me. I'm happy to share this here or elsewhere as appropriate; also happy to try anything else.

Thank you for the attention.

[Danp]

If you haven't rebooted after patching, then that could be a contributing factor.

[the_jest]

@Danp
Grr. OK I'll reboot later today (after some other tasks are finished) and report back.

I am worried about nuking the currently-working VMs. It would obviously be good to have another host for exactly such purposes. Thank you.

[MajorP93]

@the_jest According to my own tests not rebooting after patching XCP-ng hosts can cause several issues. Thats why Xen Orchestra GUI notes to reboot after updating. Documentation has further explanation for this and explains whole update procedure.

[the_jest]

I have not seen warnings to reboot after previous patchings (nor this one, that I recall).

In any case, I did reboot, and everything is fine, and I'm sorry to have wasted time and attention on this! Thank you.

[acebmxer]

@the_jest

Not showen in this picutre but this is where the message would be displayed. Next to the name of the host...