How to use NFS over TCP?

If you need NFS, it is recommended to use NFS over TCP since NFS over UDP is not very secure. All 2.4 and 2.6 kernels support NFS over TCP on the client side. Server support for TCP appears in later 2.4 kernels, and in all 2.6 kernels.

To verify whether your server supports NFS over TCP, use the wire-test command (/usr/sbin/wire-test is part of the am-utils package). If your server supports NFS over TCP, the output looks like this:

# wire-test localhost
Network 1: wire="172.16.1.0" (netnumber=172.16.1).
Network 2: wire="172.16.1.1" (netnumber=172.16.1).
My IP address is 0xac100101.
NFS Version and protocol tests to host "localhost"...
        testing vers=2, proto="udp" -> found version 2.
        testing vers=3, proto="udp" -> found version 3.
        testing vers=2, proto="tcp" -> found version 2.
        testing vers=3, proto="tcp" -> found version 3.
#

If the server does not support NFS over TCP, the output will look like this:

# wire-test localhost
Network 1: wire="172.16.1.0" (netnumber=172.16.1).
Network 2: wire="172.16.1.1" (netnumber=172.16.1).
My IP address is 0xac100101.
NFS Version and protocol tests to host "localhost"...
        testing vers=2, proto="udp" -> found version 2.
        testing vers=3, proto="udp" -> found version 3.
        testing vers=2, proto="tcp" -> failed!
        testing vers=3, proto="tcp" -> failed!
#

To mount a shared directory using NFS over TCP, use the “proto=tcp” mount option:

# mount -o proto=tcp <nfs_server_name>:/pub /mnt

Make sure the target directory, in this example /mnt, exists on the client.