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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 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 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 unin-
     terruptibly 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	     Used with NQNFS to	set the	``dead server threshold'' to the spec-
	     ified 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 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 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 perfor-
	     mance 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
		     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 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 Not Quite NFS (NQNFS) protocol.  This experimental	proto-
	     col 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 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), 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	9.3			March 29, 1995			   FreeBSD 9.3

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | BUGS

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