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MOUNT_NFS(8)            FreeBSD System Manager's Manual           MOUNT_NFS(8)

NAME
     mount_nfs - mount nfs file systems

SYNOPSIS
     mount_nfs [-23KNPTUbcdilqs] [-D deadthresh] [-I readdirsize]
               [-L leaseterm] [-R retrycnt] [-a maxreadahead] [-g maxgroups]
               [-m realm] [-o options] [-r readsize] [-t timeout]
               [-w writesize] [-x retrans] rhost:path node

DESCRIPTION
     The mount_nfs command calls the mount(2) system call to prepare and graft
     a remote nfs file system (rhost:path) on to the file system tree at the
     point node.  This command is normally executed by mount(8).  It
     implements the mount protocol as described in RFC 1094, Appendix A and
     NFS: Network File System Version 3 Protocol Specification, Appendix I.

     By default, mount_nfs keeps retrying until the mount succeeds.  This
     behaviour is intended for filesystems listed in fstab(5) that are
     critical to the boot process.  For non-critical filesystems, the -b and
     -R flags provide mechanisms to prevent the boot process from hanging if
     the server is unavailable.

     If the server becomes unresponsive while an NFS filesystem is mounted,
     any new or outstanding file operations on that filesystem will hang
     uninterruptibly until the server comes back.  To modify this default
     behaviour, see the -i and -s flags.

     The options are:

     -2      Use the NFS Version 2 protocol (the default is to try version 3
             first then version 2).  Note that NFS version 2 has a file size
             limit of 2 gigabytes.

     -3      Use the NFS Version 3 protocol.

     -D      Used with NQNFS to set the ``dead server threshold'' to the
             specified number of round trip timeout intervals.  After a ``dead
             server threshold'' of retransmit timeouts, cached data for the
             unresponsive server is assumed to still be valid.  Values may be
             set in the range of 1 - 9, with 9 referring to an ``infinite dead
             threshold'' (i.e. never assume cached data still valid).  This
             option is not generally recommended and is really an experimental
             feature.

     -I      Set the readdir read size to the specified value.  The value
             should normally be a multiple of DIRBLKSIZ that is <= the read
             size for the mount.

     -K      Pass Kerberos authenticators to the server for client-to-server
             user-credential mapping.  This requires that the kernel be built
             with the NFSKERB option.  The use of this option will prevent the
             kernel from compiling unless calls to the appropriate Kerberos
             encryption routines are provided in the NFS source.  (Refer to
             the INTERNET-DRAFT titled Authentication Mechanisms for ONC RPC,
             for more information.)

     -L      Used with NQNFS to set the lease term to the specified number of
             seconds.  Only use this argument for mounts with a large round
             trip delay.  Values are normally in the 10-30 second range.

     -N      Do not use a reserved socket port number (see below).

     -P      Use a reserved socket port number.  This flag is obsolete, and
             only retained for compatibility reasons.  Reserved port numbers
             are used by default now.  This is useful for mounting servers
             that require clients to use a reserved port number on the
             mistaken belief that this makes NFS more secure.  (For the rare
             case where the client has a trusted root account but
             untrustworthy users and the network cables are in secure areas
             this does help, but for normal desktop clients this does not
             apply.)

     -R      Set the mount retry count to the specified value.  The default is
             a retry count of zero, which means to keep retrying forever.
             There is a 60 second delay between each attempt.

     -T      Use TCP transport instead of UDP.  This is recommended for
             servers that are not on the same LAN cable as the client.  (NB:
             This is NOT supported by most non-BSD servers.)

     -U      Force the mount protocol to use UDP transport, even for TCP NFS
             mounts.  (Necessary for some old BSD servers.)

     -a      Set the read-ahead count to the specified value.  This may be in
             the range of 0 - 4, and determines how many blocks will be read
             ahead when a large file is being read sequentially.  Trying a
             value greater than 1 for this is suggested for mounts with a
             large bandwidth * delay product.

     -b      If an initial attempt to contact the server fails, fork off a
             child to keep trying the mount in the background.  Useful for
             fstab(5), where the filesystem mount is not critical to multiuser
             operation.

     -c      For UDP mount points, do not do a connect(2).  This must be used
             if the server does not reply to requests from the standard NFS
             port number 2049 or replies to requests using a different IP
             address (which can occur if the server is multi-homed).  Setting
             the vfs.nfs.nfs_ip_paranoia sysctl to 0 will make this option the
             default.

     -d      Turn off the dynamic retransmit timeout estimator.  This may be
             useful for UDP mounts that exhibit high retry rates, since it is
             possible that the dynamically estimated timeout interval is too
             short.

     -g      Set the maximum size of the group list for the credentials to the
             specified value.  This should be used for mounts on old servers
             that cannot handle a group list size of 16, as specified in RFC
             1057.  Try 8, if users in a lot of groups cannot get response
             from the mount point.

     -i      Make the mount interruptible, which implies that file system
             calls that are delayed due to an unresponsive server will fail
             with EINTR when a termination signal is posted for the process.

     -l      Used with NQNFS and NFSV3 to specify that the ReaddirPlus RPC
             should be used.  This option reduces RPC traffic for cases such
             as ``ls -l'', but tends to flood the attribute and name caches
             with prefetched entries.  Try this option and see whether
             performance improves or degrades.  Probably most useful for
             client to server network interconnects with a large bandwidth
             times delay product.

     -m      Set the Kerberos realm to the string argument.  Used with the -K
             option for mounts to other realms.

     -o      Options are specified with a -o flag followed by a comma
             separated string of options.  See the mount(8) man page for
             possible options and their meanings.  The following NFS specific
             option is also available:

             port=<port_number>
                     Use specified port number for NFS requests.  The default
                     is to query the portmapper for the NFS port.

             acregmin=<seconds>

             acregmax=<seconds>

             acdirmin=<seconds>

             acdirmax=<seconds>
                     When attributes of files are cached, a timeout calculated
                     to determine whether a given cache entry has expired.
                     These four values determine the upper and lower bounds of
                     the timeouts for ``directory'' attributes and ``regular''
                     (ie: everything else).  The default values are 3 -> 60
                     seconds for regular files, and 30 -> 60 seconds for
                     directories.  The algorithm to calculate the timeout is
                     based on the age of the file.  The older the file, the
                     longer the cache is considered valid, subject to the
                     limits above.

             Historic -o options

             Use of these options is deprecated, they are only mentioned here
             for compatibility with historic versions of mount_nfs.

             bg           Same as -b.

             conn         Same as not specifying -c.

             dumbtimer    Same as -d.

             intr         Same as -i.

             kerb         Same as -K.

             nfsv2        Same as -2.

             nfsv3        Same as -3.

             rdirplus     Same as -l.

             mntudp       Same as -U.

             resvport     Same as -P.

             seqpacket    Same as -p.

             nqnfs        Same as -q.

             soft         Same as -s.

             tcp          Same as -T.

     -q      Use the Not Quite NFS (NQNFS) protocol.  This experimental
             protocol is NFS Version 2 with leasing extensions similar to
             those found in NFS Version 3.  The interoperability of this
             protocol with other systems is very limited and its
             implementation is not widely used.  Do not use this option unless
             you know exactly what you are doing!

     -r      Set the read data size to the specified value.  It should
             normally be a power of 2 greater than or equal to 1024.  This
             should be used for UDP mounts when the ``fragments dropped due to
             timeout'' value is getting large while actively using a mount
             point.  (Use netstat(1) with the -s option to see what the
             ``fragments dropped due to timeout'' value is.)  See the -w
             option as well.

     -s      A soft mount, which implies that file system calls will fail
             after Retry round trip timeout intervals.

     -t      Set the initial retransmit timeout to the specified value.  May
             be useful for fine tuning UDP mounts over internetworks with high
             packet loss rates or an overloaded server.  Try increasing the
             interval if nfsstat(1) shows high retransmit rates while the file
             system is active or reducing the value if there is a low
             retransmit rate but long response delay observed.  (Normally, the
             -d option should be specified when using this option to manually
             tune the timeout interval.)

     -w      Set the write data size to the specified value.  Ditto the
             comments w.r.t. the -r option, but using the ``fragments dropped
             due to timeout'' value on the server instead of the client.  Note
             that both the -r and -w options should only be used as a last
             ditch effort at improving performance when mounting servers that
             do not support TCP mounts.

     -x      Set the retransmit timeout count for soft mounts to the specified
             value.

SEE ALSO
     mount(2), unmount(2), fstab(5), mount(8), nfsd(8), nfsiod(8),
     showmount(8)

BUGS
     Due to the way that Sun RPC is implemented on top of UDP (unreliable
     datagram) transport, tuning such mounts is really a black art that can
     only be expected to have limited success.  For clients mounting servers
     that are not on the same LAN cable or that tend to be overloaded, TCP
     transport is strongly recommended, but unfortunately this is restricted
     to mostly 4.4BSD servers.

FreeBSD 11.0-PRERELEASE         March 29, 1995         FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | BUGS

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