18.10. Using NFS over TCP

18.10. Using NFS over TCP

The default transport protocol for NFSv4 is TCP; however, the Red Hat Enterprise Linux 5 kernel includes support for NFS over UDP. To use NFS over UDP, include the -o udp option to mount when mounting the NFS-exported file system on the client system.

There are three ways to configure an NFS file system export. On demand via the command line (client side), automatically via the /etc/fstab file (client side), and automatically via autofs configuration files, such as /etc/auto.master and /etc/auto.misc (server side with NIS).

For example, on demand via the command line (client side):

mount -o udp shadowman.example.com:/misc/export /misc/local

When the NFS mount is specified in /etc/fstab (client side):

server:/usr/local/pub    /pub   nfs    rsize=8192,wsize=8192,timeo=14,intr,udp

When the NFS mount is specified in an autofs configuration file for a NIS server, available for NIS enabled workstations:

myproject  -rw,soft,intr,rsize=8192,wsize=8192,udp penguin.example.net:/proj52

Since the default is TCP, if the -o udp option is not specified, the NFS-exported file system is accessed via TCP.

The advantages of using TCP include the following:

The main disadvantage is that there is a very small performance hit due to the overhead associated with the TCP protocol.