Tuesday, March 12, 2019

mount.nfs Remote I/O error


Yesterday when i exported /aix/share  from AIX 7.1 to Linux client with NFS version 3 and when tried to mount on SUSE Linux 12 client with following command got error “mount.NFS: Remote I/O error”
root# mount aixNFSserver:/aix/share /linux/share
“mount.NFS: Remote I/O error”

First, I did not got why this error occurred, because everything was ok from NFS server side. Permission, client hostname entry in /etc/exports file on NFS server was correct. Then i thought that it is looking like I/O error for file system, which I exported, but on NFS server, shared file system is ok and not showing any error related I/O. After I checked that what is default NFS version for SUSE Linux 12 and found that it is NFS version 4 and observed that there are some mount option was used for mounting AIX NFS share to SUSE Linux.

Observation found:
Environment:
Source NFS server:  AIX 7.1
Version: NFS V3.
Target Linux client: SUSE Linux 12.
Default NFS Version: NFS Version 4.
Found /etc/fstab entry for NFS mount with following option for other mount which already mounted from AIX to Linux.

aixNFSserver2:/aix/soft /linux/soft nfs     defaults,nfsvers=3,rw,intr 0 0

After this observation, I did entry for /aix/share like below and executed mount command and guess what it was successful

aixNFSserver:/aix/share /linux/share nfs    defaults,nfsvers=3,rw,intr 0 0

Option and their meaning
intr : Allows NFS requests to be interrupted if the server goes down or cannot be reached.
nfsvers= option specifies which version of nfs protocol should use, If admin not choose any version NFS will use highest supported version

What was the reason that causing previously mount failure with error “mount.NFS: Remote I/O error” ??

Answer:
Previously we did not specified NFS version while mounting share we directly executing mount command like below.

root# mount aixNFSserver:/aix/share /linux/share

 And we didn’t specified mount option “nfsvers=3” because default NFS version of SUSE 12 is NFSv4 and exported NFS version from AIX NFS server is NFSv3. While mounting we didn’t mention any NFS version so at Linux side NFS chossed highest supported NFS version and that was NFS v4 and this causing Remote I/O error while mounting.

Also we can specify mount option while executing mount command. In below example shown how to specify mount option while mounting NFS share from AIX to Suse Linux to avoid error "mount.NFS: Remote I/O error"

#mount –t nfs aixNFSserver:/aix/share /linux/share –o nfsvers=3

Or

First make entry in /etc/fstab like below and then execute command #mount –a.
aixNFSserver:/aix/share /linux/share nfs    defaults,nfsvers=3,rw,intr 0 0

Finally we conclude that if we specify correct nfs version while mounting NFS share we can avoid error mount.NFS: Remote I/O error.


Thanks !!!!!

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