.BR nfs
file system type and specify
.BR nfsvers=2 .
-Version 2 is the default protocol version for the
-.BR nfs
-file system type when
-.BR nfsvers=
-is not specified on the mount command.
To mount via NFS version 3, use the
.BR nfs
file system type and specify
.BR nfsvers=3 .
+Version 3 is the default protocol version for the
+.BR nfs
+file system type when
+.BR nfsvers=
+is not specified on the mount command and both client and server
+support it.
To mount via NFS version 4, use the
.BR nfs4
file system type.
These file system types share similar mount options;
the differences are listed below.
.P
-Here is an example from an \fI/etc/fstab\fP file for an NFSv2 mount
-over UDP.
+Here is an example from an \fI/etc/fstab\fP file for an NFSv3 mount
+over TCP.
.sp
.nf
.ta 2.5i +0.75i +0.75i +1.0i
.TP 1.5i
.I nolock
Disable NFS locking. Do not start lockd.
-This has to be used with some old NFS servers
+This is appropriate for mounting the root filesystem or
+.B /usr
+or
+.BR /var .
+These filesystems are typically either read-only or not shared, and in
+those cases, remote locking is not needed.
+This also needs to be used with some old NFS servers
that don't support locking.
+.br
+Note that applications can still get locks on files, but the locks
+only provide exclusion locally. Other clients mounting the same
+filesystem will not be able to detect the locks.
.TP 1.5i
.I bg
If the first NFS mount attempt times out, retry the mount
or privacy.
.TP 1.5i
.I tcp
-Mount the NFS filesystem using the TCP protocol instead of the
-default UDP protocol. Many NFS servers only support UDP.
+Mount the NFS filesystem using the TCP protocol. This is the default
+if it is supported by both client and server. Many NFS servers only
+support UDP.
.TP 1.5i
.I udp
-Mount the NFS filesystem using the UDP protocol. This
-is the default.
+Mount the NFS filesystem using the UDP protocol.
+.TP 1.5i
+.I nordirplus
+Disables NFSv3 READDIRPLUS RPCs. Use this option when
+mounting servers that don't support or have broken
+READDIRPLUS implementations.
+.TP 1.5i
+.I nosharecache
+As of kernel 2.6.18, it is no longer possible to mount the same
+same filesystem with different mount options to a new mountpoint.
+It was deemed unsafe to do so, since cached data cannot be shared
+between the two mountpoints. In consequence, files or directories
+that were common to both mountpoint subtrees could often be seen to
+be out of sync following an update.
+.br
+This option allows administrators to select the pre-2.6.18 behaviour,
+permitting the same filesystem to be mounted with different mount
+options.
+.br
+.B Beware:
+Use of this option is not recommended unless you are certain that there
+are no hard links or subtrees of this mountpoint that are mounted
+elsewhere.
.P
All of the non-value options have corresponding nooption forms.
For example, nointr means don't allow file operations to be
server performance penalty but it allows two different NFS clients
to get reasonable good results when both clients are actively
writing to common filesystem on the server.
+.TP 1.5i
+.I nosharecache
+As of kernel 2.6.18, it is no longer possible to mount the same
+same filesystem with different mount options to a new mountpoint.
+It was deemed unsafe to do so, since cached data cannot be shared
+between the two mountpoints. In consequence, files or directories
+that were common to both mountpoint subtrees could often be seen to
+be out of sync following an update.
+.br
+This option allows administrators to select the pre-2.6.18 behaviour,
+permitting the same filesystem to be mounted with different mount
+options.
+.br
+.B Beware:
+Use of this option is not recommended unless you are certain that there
+are no hard links or subtrees of this mountpoint that are mounted
+elsewhere.
.P
All of the non-value options have corresponding nooption forms.
For example, nointr means don't allow file operations to be
.SH AUTHOR
"Rick Sladkey" <jrs@world.std.com>
.SH BUGS
-The posix, and nocto options are parsed by mount
-but currently are silently ignored.
-.P
-The tcp and namlen options are implemented but are not currently
-supported by the Linux kernel.
-.P
-The umount command should notify the server
-when an NFS filesystem is unmounted.
.P
Checking files on NFS filesystem referenced by file descriptors (i.e. the
.BR fcntl
projects / nfs-utils.git / blobdiff