[CentOS] nfsvers and nfs-utils-1.3.0-0.48.el7

Thu Oct 12 17:33:29 UTC 2017
Paul Heinlein <heinlein at madboa.com>

We encountered a weird problem today, and I thought some of you might 
like to hear the solution.

The underlying change was listed in the 7.4 changelog, so it's not a 
bug, but it may drive you buggy.

The majority of our HPC cluster nodes run CentOS 7, though the exact 
patch levels vary from node to node. None is older than 7.3, but a few 
newer nodes were kickstarted right to 7.4.

The problem was that our mounts of Isilon NFS exports were failing 
randomly among the nodes. Routing was fine. Network connectivity was 

The short answer is that the default in 7.4, and I think in the 
nfs-utils-1.3.0-0.48.el7 package in particular, has changed. While NFS 
v4.0 was the default up to 7.3, the 7.4 protocols are subtly 

1. Try NFS v4.1 first
2. Fail down to NFS v3
3. Fail down to NFS v2

The problem is that our Isilon works with NFS v4.0, not 4.1, but 4.0 
is not in the fail-down path.

The short-term answer is to specify nfsvers=4.0 in our autofs 
configuration files, which works like a charm.

Like I said, this was an announced change, but the implications 
escaped us until now. So this little writeup is just for the record.

Paul Heinlein
heinlein at madboa.com
45°38' N, 122°6' W