I have several external mounts that are mounted using NFS.

These were working perfectly when I had Ubuntu 14.04, however, I have just updated to 16.04.1 and now they are not mounting.

They are not mounting on startup as specified in /etc/fstab nor am I able to mount them manually.

The fstab reads: /external-storage/server1 nfs user 0 0

All the other mounts are in the fstab following the same model.

When I run dmseg I get the following error message for NFS:

NFS: nfs4_discover_server_trunking unhandled error -512. Exiting with error EIO

Any help would be greatly appreciated!


I saw the same problem in 16.04 and recently "fixed" it (with a workaround to disable a kernel module).

If you manually mount the filesystem, then check /etc/mtab, you'll probably see a bunch of junk added to the options, e.g. mine became:


The key insight is the sec=sys bit, that means NFS isn't using any of the GSSAPI/Kerberos authentication stuff. (From context in mailing list issues, I've gleaned the the "-512" error is a generic error for when the "AUTH_GSS upcall" fails.)

You'd expect passing sec=sys yourself in /etc/fstab would fix this, but it didn't work for me. Nor did explicitly putting NEED_GSSD=no in /etc/default/nfs-common.

What did work, following this thread was just blacklisting the rpcsec_gss_krb5 module via modprobe.d:

echo 'blacklist rpcsec_gss_krb5' > /etc/modprobe.d/blacklist-rpcsec-gss-krb5.conf

The other caveat is that this is probably a bug, and should just work. There is, for example, this recent Redhat bug report for "nfs4_discover_server_trunking unhandled error -512" which has been marked as a duplicate of a non-public bug.


If you're desperate, you could look at the changelogs for the NFS packages, all the way back to nfs-utils (0.1.3-1) (current version is 1:1.2.8-9ubuntu12 Ubuntu:16.04/xenial), read the files from the top down to the NFS versions you're running on 12.04:

+w3@aardvark:~(0)$ dpkg -l nfs\*
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                        Version    Architecture        Description
un  nfs-common                 <none>      <none>    (no description available)
un  nfs-kernel-server          <none>      <none>    (no description available)
+w3@aardvark:~(0)$ apt-get changelog nfs-common
Get:1 http://changelogs.ubuntu.com nfs-utils 1:1.2.8-9ubuntu12 Changelog [131 kB]
Fetched 131 kB in 1s (113 kB/s)
+w3@aardvark:~(0)$ apt-get changelog nfs-kernel-server
Get:1 http://changelogs.ubuntu.com nfs-utils 1:1.2.8-9ubuntu12 Changelog [131 kB]
Fetched 131 kB in 1s (118 kB/s)
  • Probably not so useful, because the root cause of most NFS regressions I've seen has been in the linux-image package not nfs-utils. – Dominic Scheirlinck May 9 '17 at 2:01

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