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

     mount_nfs -- mount	NFS file systems

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

     The mount_nfs utility 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 imple-
     ments 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 be-
     haviour is	intended for file systems listed in fstab(5) that are critical
     to	the boot process.  For non-critical file systems, 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 file system is mounted,
     any new or	outstanding file operations on that file system	will hang un-
     interruptibly until the server comes back.	 To modify this	default	behav-
     iour, 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	     Set the "dead server threshold" to	the specified number of	round
	     trip timeout intervals before a "server not responding" message
	     is	displayed.

     -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.

     -L	     Do	not forward fcntl(2) locks over	the wire.  All locks will be
	     local and not seen	by the server and likewise not seen by other
	     NFS clients.  This	removes	the need to run	the rpcbind(8) service
	     and the rpc.statd(8) and rpc.lockd(8) servers on the client.
	     Note that this option will	only be	honored	when performing	the
	     initial mount, it will be silently	ignored	if used	while updating
	     the mount options.

     -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.  (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 file system mount is not critical to multi-
	     user 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 ad-
	     dress (which can occur if the server is multi-homed).  Setting
	     the vfs.nfs.nfs_ip_paranoia sysctl	to 0 will make this option the

     -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

     -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.

     -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 options
	     are also available:

		     Use specified port	number for NFS requests.  The default
		     is	to query the portmapper	for the	NFS port.




		     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.

	     noinet4, noinet6
		     Disables AF_INET or AF_INET6 connections.	Useful for
		     hosts that	have both an A record and an AAAA record for
		     the same name.

	     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.

	     lockd	Same as	not specifying -L.

	     nfsv2	Same as	-2.

	     nfsv3	Same as	-3.

	     rdirplus	Same as	-l.

	     mntudp	Same as	-U.

	     resvport	Same as	-P.

	     soft	Same as	-s.

	     tcp	Same as	-T.

     -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 retrycnt 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

     mount(2), unmount(2), fstab(5), mount(8), nfsd(8),	nfsiod(8),

     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.

BSD				 May 11, 2003				   BSD


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