[Bug 1881847] Re: If NFS server reboots, client somethings fails to remount the file system properly

[Andreas Hasenack]

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 at 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 at 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

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https://bugs.launchpad.net/bugs/1881847

Title:
  If NFS server reboots, client somethings fails to remount the file
  system properly

Status in nfs-utils package in Ubuntu:
  New

Bug description:
  If the NFS server reboots, sometimes client servers fail to re-
  establish the NFS mount properly.  This is using NFS v4.2.  The client
  machine will hang if I try to do a df when an NFS mount is in this
  condition.  Attempting to access a file will likewise hang
  indefinitely.  This is a problem with the stock 5.3.0.x kernel and it
  is a problem with 5.6 still.  I have not tried 5.7 yet.  I filed this
  against nfs-kernel, but I am not 100% sure it is not nfs-common but
  there is some sort of communications not happening between them.

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: nfs-kernel-server 1:1.3.4-2.5ubuntu3
  Uname: Linux 5.6.0 x86_64
  ApportVersion: 2.20.11-0ubuntu27.2
  Architecture: amd64
  CasperMD5CheckResult: skip
  CurrentDesktop: MATE
  Date: Tue Jun  2 21:34:31 2020
  InstallationDate: Installed on 2017-05-27 (1102 days ago)
  InstallationMedia: Ubuntu-MATE 17.04 "Zesty Zapus" - Release amd64 (20170412)
  SourcePackage: nfs-utils
  UpgradeStatus: Upgraded to focal on 2020-04-26 (38 days ago)

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