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

NAME
     mount_nfs — mount nfs file systems

SYNOPSIS
     mount_nfs [-3KPTUbcdilqs] [-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.

     The options are:

     -3	     Use the NFS Version 3 protocol (Version 2 is the default).

     -D	     Used with NQNFS to set the “dead server threshold” to the speci‐
	     fied 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.  (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.

     -P	     Use a reserved socket port number.	 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 untrusworthy
	     users and the network cables are in secure areas this does help,
	     but for normal desktop clients this does not apply.)

     -R	     Set the retry count for doing the mount to the specified value.

     -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
	     for servers that do not reply to requests from the standard NFS
	     port number 2049.

     -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 sepa‐
	     rated string of options.  See the mount(8) man page for possible
	     options and their meanings.

     -q	     Use the leasing extensions to the NFS Version 3 protocol to main‐
	     tain cache consistency.  This protocol version 2 revision to Not
	     Quite Nfs (NQNFS) is only supported by this updated release of
	     NFS code.	It is not backwards compatible with the version 1
	     NQNFS protocol that was part of the first release of 4.4BSD-Lite.
	     To interoperate with a first release 4.4BSD-Lite NFS system you
	     will have to avoid this option until you have had an oppurtunity
	     to upgrade the NFS code to release 2 of 4.4BSD-Lite on all your
	     systems.

     -r	     Set the read data size to the specified value.  It should nor‐
	     mally 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 retrans‐
	     mit 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 com‐
	     ments 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)

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.

4.4BSD				March 29, 1995				4.4BSD

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