9.5. Common NFS Mount Options

Beyond mounting a file system with NFS on a remote host, it is also possible to specify other options at mount time to make the mounted share easier to use. These options can be used with manual mount commands, /etc/fstab settings, and autofs.
The following are options commonly used for NFS mounts:
Allows NFS requests to be interrupted if the server goes down or cannot be reached.
Specifies how the kernel should manage its cache of directory entries for a given mount point. Valid arguments for mode are all, none, or pos/positive.
Specifies which version of the NFS protocol to use, where version is 2, 3, or 4. This is useful for hosts that run multiple NFS servers. If no version is specified, NFS uses the highest version supported by the kernel and mount command.
The option vers is identical to nfsvers, and is included in this release for compatibility reasons.
Turns off all ACL processing. This may be needed when interfacing with older versions of Red Hat Enterprise Linux, Red Hat Linux, or Solaris, since the most recent ACL technology is not compatible with older systems.
Disables file locking. This setting is occasionally required when connecting to older NFS servers.
Prevents execution of binaries on mounted file systems. This is useful if the system is mounting a non-Linux file system containing incompatible binaries.
Disables set-user-identifier or set-group-identifier bits. This prevents remote users from gaining higher privileges by running a setuid program.
port=num — Specifies the numeric value of the NFS server port. If num is 0 (the default), then mount queries the remote host's rpcbind service for the port number to use. If the remote host's NFS daemon is not registered with its rpcbind service, the standard NFS port number of TCP 2049 is used instead.
rsize=num and wsize=num
These settings speed up NFS communication for reads (rsize) and writes (wsize) by setting a larger data block size (num, in bytes), to be transferred at one time. Be careful when changing these values; some older Linux kernels and network cards do not work well with larger block sizes.


If an rsize value is not specified, or if the specified value is larger than the maximum that either client or server can support, then the client and server negotiate the largest resize value they can both support.
Specifies the type of security to utilize when authenticating an NFS connection. Its default setting is sec=sys, which uses local UNIX UIDs and GIDs by using AUTH_SYS to authenticate NFS operations.
sec=krb5 uses Kerberos V5 instead of local UNIX UIDs and GIDs to authenticate users.
sec=krb5i uses Kerberos V5 for user authentication and performs integrity checking of NFS operations using secure checksums to prevent data tampering.
sec=krb5p uses Kerberos V5 for user authentication, integrity checking, and encrypts NFS traffic to prevent traffic sniffing. This is the most secure setting, but it also involves the most performance overhead.
Instructs the NFS mount to use the TCP protocol.
Instructs the NFS mount to use the UDP protocol.
For a complete list of options and more detailed information on each one, refer to man mount and man nfs.