Documentation and debugging for NFSv4

[Greg Veldman]

On Fri, May 22, 2020 at 07:43:02PM +0100, Norman Gray wrote:
[snip]
> I now go to another CentOS 7.8 machine
> 
>      client3# mount -tnfs server:/astro/norman /mnt
>      client3# mount|grep /mnt
>      server:/astro/norman on /mnt type nfs4 
> (rw,relatime,vers=4.1,rsize=131072,wsize=131072,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=130.209.202.212,local_lock=none,addr=130.209.45.61)
>      client3# ls /mnt
>      ls: reading directory /mnt: Input/output error
> 
> Nothing!  The same thing -- an apparently successful mount, and then
> an I/O error -- happens when I let the automounter do the work.

Based on this and your subsequent response to Doug/Remy, I
think the next thing I'd check would be the idmap settings.
It sounds like you may have a domain mismatch.  All the idmap
daemons on both client and server must be running and must agree
on the domain name (doesn't really matter what it is, they just
have to agree).  On FreeBSD this is specified with the -domain
arg to nfsuserd (which looks like it can also be put in rc.conf).
On Linux it's set with the Domain keyword in /etc/idmapd.conf.
Various implementations of the software attempt to calculate a
default domain if none is given, using different methods to do
so.  It's much safer to pick something yourself and explicitly
set it everywhere.

-- 
Greg Veldman