8.4. Common NFS Mount Options

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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:
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 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 sometimes required when connecting to very old 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.
Specifies the numeric value of the NFS server port. If num is 0 (the default value), 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 options set the maximum number of bytes to be transfered in a single NFS read or write operation.
There is no fixed default value for rsize and wsize. By default, NFS uses the largest possible value that both the server and the client support. In Red Hat Enterprise Linux 7, the client and server maximum is 1,048,576 bytes. For more details, see the What are the default and maximum values for rsize and wsize with NFS mounts? KBase article.
Security flavors to use for accessing files on the mounted export. The flavors value is a colon-separated list of one or more security flavors.
By default, the client attempts to find a security flavor that both the client and the server support. If the server does not support any of the selected flavors, the mount operation fails.
sec=sys uses local UNIX UIDs and GIDs. These use 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 more information, see man mount and man nfs.
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