Comment 2 for bug 1881847

With NFSv4, user and group information is sent on the wire as names, instead of uids. And these names are qualified with a domain. So for example an exported directory containing files for the "ubuntu" user will have the ownership sent to NFSv4 clients as "ubuntu@DOMAIN", where "DOMAIN" is the DNS domain of the server.

Whave I have seen in some testing is that after a reboot, for some reason (probably service ordering), the NFS server bits do not know yet the domain of the machine, and then this becomes "localdomain", and the user is sent to the client as "ubuntu@localdomain". The client, being on the same DNS domain, decides that "localdomain" is none of its business, and declares that user as "nobody".

You said there was a "hang", but maybe the issue above is realted somehow? One way to see it is in the client logs, where "nfsidmap" is called. If you configure /etc/request-key.d/id_resolver.conf to call nfidmap with extra "-v -v -v" in the command line, it will be more verbose in /var/log/syslog and say which user it's trying to resolve.

If you see the "localdomain" issue, then try hardcoding the domain in /etc/idmapd.conf on both the server and the client, to your actual DNS domain, and see if that helps.

Hope this helps