Yesterday I upgraded my work machine to Ubuntu 21.10. Wrong move. 

I run test systems on LXD. For compat reasons, we stopped at version 4.9.
But this version stopped working with the new 5.13 kernel. The symptom
was that few commands really finished exeuting. I tried using the old
5.11 kernel, but the system didn't even finish booting (it stayed waiting
for a wireguard service that would never succeed because the underlaying
network was not connected yet).

So next I tried upgrading the LXD conector (because we really use
terraform), then upgrading LXD itself (and hoping our issues were fixed),
but still no cigar.

So I went full nuclear, purged LXD and reinstalled. Not my preferred way
to solve things, but I was already wasting a full day on this. This
seemed to show some progress, but then I started getting this error in
terraform (which actually comes from the provider):

```
lxd_network.singlenode: Refreshing state... [id=singlenode]
Error: Unable to create client for remote [localhost]: 
  Get "https://127.0.0.1:5555/1.0": 
      x509: certificate signed by unknown authority (possibly because of 
            "x509: ECDSA verification failure" while trying to verify candidate 
                   authority certificate "root@nimbus")
```

(I wrapped the line a little so it's more readable).

Ok, certificate issue, even when `accept_remote_certificate = true` was
configured on the provider. The weird part was that f.i. `lxd list` was
working fine. I run `lxd remote` and it was not showing localhost, so I
tried 
`lxc remote add nimbus 127.0.0.1:5555 --accept-certificate --password=xxxxx`
but I was _still_ getting the same error!

Then a coworker reminded me: you have to remove 
`~/.config/lxc/servercerts/remote.crt` so it forgets about it and gets 
a new one.

Now I have issues that might be related to the new LXD provider for
terraform, but at least LXD is working fine again.