How do I set the NFS4 client callback port to a specific port?

Solution Verified - Updated

Environment

  • Red Hat Enterprise Linux (NFS client)
  • NFS4

Issue

  • How do I set the NFS4 client callback port to a specific port?

Resolution

Red Hat Enterprise Linux - all versions (NFS 4.1 and above)

NFS v4.1 and later uses the pre-existing client port for callbacks, so the callback port cannot be set separately.

Red Hat Enterprise Linux 5 - 7 (NFS 4.0)

The kernel tunable fs.nfs.nfs_callback_tcpport can be used to set the NFS4 client callback port to a specific port.
This option can be set at runtime as follows. Once set, all new NFS4 mount requests will use the new callback port.

# /sbin/sysctl -w fs.nfs.nfs_callback_tcpport=60000

On RHEL6 and RHEL7, the callback port can be made permanent by entering the option into modprobe, for example:

echo "options nfs callback_tcpport=60000" >> /etc/modprobe.d/nfs-callbacks.conf

On RHEL5, the callback port can be made permanent by editing /etc/modprobe.d/modprobe.conf.dist with the line:

install nfs /sbin/modprobe --first-time --ignore-install nfs && { /sbin/sysctl -w fs.nfs.nfs_callback_tcpport=60000; }

To see the modprobe option take effect, umount any NFS4 mount point, rmmod and modprobe the NFS module, then remount the share. For example

# umount /mnt/nfs4
# rmmod nfs
# modprobe nfs
# mount nfs-server:/export /mnt/nfs4

To verify the callback port has been set to what you'd expect, make sure at least one NFS4 share is mounted, then check for a TCP LISTEN port equal to the port you set.

# grep nfs4 /proc/mounts
nfs-server:/export /mnt/nfs4 nfs4 rw,relatime,vers=4,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.122.46,minorversion=0,local_lock=none,addr=192.168.122.2 0 0
# netstat -an | grep tcp | grep LIST | grep 60000
tcp        0      0 0.0.0.0:60000               0.0.0.0:*                   LISTEN      
tcp        0      0 :::60000                    :::*                        LISTEN
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