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MOUNT_NFS(8)		  BSD 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.

     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 speci-
	     fied number of round trip timeout intervals.  After a "dead
	     server threshold" of retransmit timeouts, cached data for the un-
	     responsive	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 op-
	     tion 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.

     -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	 This flag is obsolete,	and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 mis-
	     taken 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 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.  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 di-
		     rectories.	 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 lim-
		     its 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 leasing extensions	to the NFS Version 3 protocol to main-
	     tain cache	consistency.  This protocol Version 2, referred	to as
	     Not Quite Nfs (NQNFS), is only supported by this updated release
	     of	NFS code.  (It is not backwards	compatible with	the release of
	     NQNFS that	went out on 4.4BSD-Lite. To interoperate with a
	     4.4BSD-Lite NFS system you	will have to avoid this	option until
	     you have had an opportunity to upgrade the	NFS code on all	your
	     4.4BSD-Lite based 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 af-
	     ter 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 op-
	     tion 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

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | BUGS

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