The fifth and sixth fields on each line are not used
by NFS, thus conventionally each contain the digit zero. For example:
.P
-.SP
-.NF
-.TA 2.5i +0.75i +0.75i +1.0i
+.nf
+.ta 8n +14n +14n +9n +20n
server:path /mountpoint fstype option,option,... 0 0
-.FI
+.fi
.P
The server's hostname and export pathname
are separated by a colon, while
.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)
option.
.TP 1.5i
.BI timeo= n
-The time (in tenths of a second) the NFS client waits for a
-response before it retries an NFS request. If this
-option is not specified, requests are retried every
-60 seconds for NFS over TCP.
-The NFS client does not perform any kind of timeout backoff
-for NFS over TCP.
+The time in deciseconds (tenths of a second) the NFS client waits for a
+response before it retries an NFS request.
+.IP
+For NFS over TCP the default
+.B timeo
+value is 600 (60 seconds).
+The NFS client performs linear backoff: After each retransmission the
+timeout is increased by
+.BR timeo
+up to the maximum of 600 seconds.
.IP
However, for NFS over UDP, the client uses an adaptive
algorithm to estimate an appropriate timeout value for frequently used
.BR krb5p ,
.BR lkey ,
.BR lkeyi ,
-.BR lkeyp ,
-.BR spkm ,
-.BR spkmi ,
and
-.BR spkmp .
+.BR lkeyp ,
Refer to the SECURITY CONSIDERATIONS section for details.
.TP 1.5i
.BR sharecache " / " nosharecache
.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
is specified, the client assumes that POSIX locks are local and uses NLM
sideband protocol to lock files when flock locks are used.
.IP
-To support legacy flock behavior similar to that of NFS clients < 2.6.12, use
-'local_lock=flock'. This option is required when exporting NFS mounts via
+To support legacy flock behavior similar to that of NFS clients < 2.6.12,
+use 'local_lock=flock'. This option is required when exporting NFS mounts via
Samba as Samba maps Windows share mode locks as flock. Since NFS clients >
2.6.12 implement flock by emulating POSIX locks, this will result in
conflicting locks.
.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
file causes the mount command to negotiate
reasonable defaults for NFS behavior.
.P
-.NF
-.TA 2.5i +0.7i +0.7i +.7i
+.nf
+.ta 8n +16n +6n +6n +30n
server:/export /mnt nfs defaults 0 0
-.FI
+.fi
.P
Here is an example from an /etc/fstab file for an NFS version 2 mount over UDP.
.P
-.NF
-.TA 2.5i +0.7i +0.7i +.7i
+.nf
+.ta 8n +16n +6n +6n +30n
server:/export /mnt nfs nfsvers=2,proto=udp 0 0
-.FI
+.fi
.P
Try this example to mount using NFS version 4 over TCP
with Kerberos 5 mutual authentication.
.P
-.NF
-.TA 2.5i +0.7i +0.7i +.7i
+.nf
+.ta 8n +16n +6n +6n +30n
server:/export /mnt nfs4 sec=krb5 0 0
-.FI
+.fi
.P
This example can be used to mount /usr over NFS.
.P
-.NF
-.TA 2.5i +0.7i +0.7i +.7i
+.nf
+.ta 8n +16n +6n +6n +30n
server:/export /usr nfs ro,nolock,nocto,actimeo=3600 0 0
-.FI
+.fi
.P
This example shows how to mount an NFS server
using a raw IPv6 link-local address.
.P
-.NF
-.TA 2.5i +0.7i +0.7i +.7i
+.nf
+.ta 8n +40n +5n +4n +9n
[fe80::215:c5ff:fb3e:e2b1%eth0]:/export /mnt nfs defaults 0 0
-.FI
+.fi
.SH "TRANSPORT METHODS"
NFS clients send requests to NFS servers via
Remote Procedure Calls, or
to prevent data exposure during network transit; however,
expect some performance impact
when using integrity checking or encryption.
-Similar support for other forms of cryptographic security (such as lipkey and SPKM3)
+Similar support for other forms of cryptographic security (such as lipkey)
is also available.
.P
The NFS version 4 protocol allows
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 .
-.P
+.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 8n
+ 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