.P
The
.I fstype
-field contains "nfs", for whatever version of the protocol.
-The
-.B nfs
-allow several mount options, which are described below.
+field contains "nfs". Use of the "nfs4" fstype in
+.I /etc/fstab
+is deprecated.
.SH "MOUNT OPTIONS"
Refer to
.BR mount (8)
.IP
The DATA AND METADATA COHERENCE section contains a
detailed discussion of these trade-offs.
-.SS "Options for versions 2 and 3 only"
+.SS "Options for NFS versions 2 and 3 only"
Use these options, along with the options in the above subsection,
-for NFSv2/v3 only. They will be ignored for newer versions.
+for NFS versions 2 and 3 only.
.TP 1.5i
.BI proto= netid
The transport protocol name and protocol family the NFS client uses
.BI nfsvers= n
The NFS protocol version number used to contact the server's NFS service.
If the server does not support the requested version, the mount request fails.
-If this option is not specified, the client negociate a suitable version with
+If this option is not specified, the client negotiates a suitable version with
the server, trying version 4 first, version 3 second, and version 2 last.
.TP 1.5i
.BI vers= n
.IP
NOTE: When used together, the 'local_lock' mount option will be overridden
by 'nolock'/'lock' mount option.
-.SS "Options for version 4 only"
+.SS "Options for NFS version 4 only"
Use these options, along with the options in the first subsection above,
-for NFSv4 only. They will be ignored with older versions.
+for NFS version 4 and newer.
.TP 1.5i
.BI proto= netid
The transport protocol name and protocol family the NFS client uses
NFS version 4 ACLs are not fully compatible with POSIX ACLs; as such,
some translation between the two is required
in an environment that mixes POSIX ACLs and NFS version 4.
-.SH FILES
-.TP 1.5i
-.I /etc/fstab
-file system table
-.SH BUGS
-The generic
-.B remount
-option is not fully supported.
-Generic options, such as
-.BR rw " and " ro
-can be modified using the
-.B remount
-option,
-but NFS-specific options are not all supported.
+.SH "THE REMOUNT OPTION"
+Generic mount options such as
+.BR rw " and " sync
+can be modified on NFS mount points using the
+.BR remount
+option.
+See
+.BR mount (8)
+for more information on generic mount options.
+.P
+With few exceptions, NFS-specific options
+are not able to be modified during a remount.
The underlying transport or NFS version
cannot be changed by a remount, for example.
+.P
Performing a remount on an NFS file system mounted with the
.B noac
option may have unintended consequences.
The
.B noac
-option is a mixture of a generic option,
+option is a combination of the generic option
.BR sync ,
-and an NFS-specific option
+and the NFS-specific option
.BR actimeo=0 .
+.SS "Unmounting after a remount"
+For mount points that use NFS versions 2 or 3, the NFS umount subcommand
+depends on knowing the original set of mount options used to perform the
+MNT operation.
+These options are stored on disk by the NFS mount subcommand,
+and can be erased by a remount.
+.P
+To ensure that the saved mount options are not erased during a remount,
+specify either the local mount directory, or the server hostname and
+export pathname, but not both, during a remount. For example,
+.P
+.NF
+.TA 2.5i
+ mount -o remount,ro /mnt
+.FI
.P
+merges the mount option
+.B ro
+with the mount options already saved on disk for the NFS server mounted at /mnt.
+.SH FILES
+.TP 1.5i
+.I /etc/fstab
+file system table
+.SH BUGS
Before 2.4.7, the Linux NFS client did not support NFS over TCP.
.P
Before 2.4.20, the Linux NFS client used a heuristic