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

     mount_nfs -- mount	NFS file systems

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

     The mount_nfs utility calls the nmount(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 im-
     plements 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 bg and retrycnt
     options 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 intr	and soft options.

     The options are:

     -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:




		     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.

		     Set four cache timeouts above to specified	value.

		     This option can be	used along with	-o gssname to specify
		     that all operations should	use the	host-based initiator
		     credential.  This may be used for clients that run	system
		     daemons that need to access files on the NFSv4 mounted

	     bg	     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 multiuser operation.

		     Set the "dead server threshold" to	the specified number
		     of	round trip timeout intervals before a "server not
		     responding" message is displayed.

		     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 esti-
		     mated timeout interval is too short.

	     fg	     Same as not specifying bg.

		     This option can be	used with the KerberosV	security fla-
		     vors for NFSv4 mounts to specify the
		     "service-principal-name" of a host-based entry in the de-
		     fault keytab file that is used for	system operations.  It
		     allows the	mount to be performed by "root"	and avoids
		     problems with cached credentials for the system opera-
		     tions expiring.  The "service-prinicpal-name" should be
		     specified without instance	or domain and is typically
		     "host", "nfs" or "root".

	     hard    Same as not specifying soft.

	     intr    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.

		     Set the maximum size of the group list for	the creden-
		     tials 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.

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

		     Override the default of NFS_DEFAULT_NAMETIMEO for the
		     timeout (in seconds) for positive name cache entries.  If
		     this is set to 0 it disables positive name	caching	for
		     the mount point.

		     Override the default of NFS_DEFAULT_NEGNAMETIMEO for the
		     timeout (in seconds) for negative name cache entries. If
		     this is set to 0 it disables negative name	caching	for
		     the mount point.

	     nfsv2   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.

	     nfsv3   Use the NFS Version 3 protocol.

	     nfsv4   Use the NFS Version 4 protocol.  This option will force
		     the mount to use TCP transport.

		     Override the default of 0 for the minor version of	the
		     NFS Version 4 protocol.  The only minor version currently
		     supported is 1.  This option is only meaningful when used
		     with the nfsv4 option.

		     Make a minor version 1 of the NFS Version 4 protocol
		     mount use a single	OpenOwner for all Opens.  This may be
		     useful for	a server with a	very low limit on OpenOwners,
		     such as AmazonEFS.	 It can	only be	used with an NFSv4.1
		     mount.  It	may not	work correctly when Delegations	are
		     being issued by a server, but note	that the AmazonEFS
		     server does not issued delegations	at this	time.

	     pnfs    Enable support for	parallel NFS (pNFS) for	minor version
		     1 of the NFS Version 4 protocol.  This option is only
		     meaningful	when used with the minorversion	option.

	     noac    Disable attribute caching.

	     noconn  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 us-
		     ing 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.

	     nocto   Normally, NFS clients maintain the	close-to-open cache
		     coherency.	 This works by flushing	at close time and
		     checking at open time.  Checking at open time is imple-
		     mented by getting attributes from the server and purging
		     the data cache if they do not match attributes cached by
		     the client.

		     This option disables checking at open time.  It may im-
		     prove performance for read-only mounts, but should	only
		     be	used if	the data on the	server changes rarely.	Be
		     sure to understand	the consequences before	enabling this

	     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.

		     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 op-
		     tion will only be honored when performing the initial
		     mount, it will be silently	ignored	if used	while updating
		     the mount options.

		     This mount	option allows the NFS client to	combine	non-
		     contiguous	byte ranges being written such that the	dirty
		     byte range	becomes	a superset of the bytes	that are
		     dirty.  This reduces the number of	writes significantly
		     for software builds.  The merging of byte ranges isn't
		     done if the file has been file locked, since most appli-
		     cations modifying a file from multiple clients will use
		     file locking.  As such, this option could result in a
		     corrupted file for	the rare case of an application	modi-
		     fying the file from multiple clients concurrently without
		     using file	locking.

		     For the RPCSEC_GSS	security flavors, such as krb5,	krb5i
		     and krb5p,	this option sets the name of the host based
		     principal name expected by	the server. This option	over-
		     rides the default,	which will be ``nfs@<server-fqdn>''
		     and should	normally be sufficient.

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

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

		     Specify transport protocol	version	to use.	 Currently,
		     they are:

		     udp -   Use UDP over IPv4
		     tcp -   Use TCP over IPv4
		     udp6 -  Use UDP over IPv6
		     tcp6 -  Use TCP over IPv6

		     Used with NFSV3 to	specify	that the ReaddirPlus RPC
		     should be used.  For NFSV4, setting this option has a
		     similar effect, in	that it	will make the Readdir Opera-
		     tion get more attributes.	This option reduces RPC	traf-
		     fic for cases such	as "ls -l", but	tends to flood the at-
		     tribute and name caches with prefetched entries.  Try
		     this option and see whether performance improves or de-
		     grades.  Probably most useful for client to server	net-
		     work interconnects	with a large bandwidth times delay

		     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 prod-

		     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.

		     Use a reserved socket port	number.	 This flag is obso-
		     lete, and only retained for compatibility reasons.	 Re-
		     served 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.)

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

		     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.

		     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 ac-
		     tively using a mount point.  (Use netstat(1) with the -s
		     option to see what	the "fragments dropped due to timeout"
		     value is.)

		     This option specifies what	security flavor	should be used
		     for the mount.  Currently,	they are:

		     krb5 -  Use KerberosV authentication
		     krb5i - Use KerberosV authentication and
			     apply integrity checksums to RPCs
		     krb5p - Use KerberosV authentication and
			     encrypt the RPC data
		     sys -   The default AUTH_SYS, which uses a
			     uid + gid list authenticator

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

	     tcp     Use TCP transport.	 This is the default option, as	it
		     provides for increased reliability	on both	LAN and	WAN
		     configurations compared to	UDP.  Some old NFS servers do
		     not support this method; UDP mounts may be	required for

		     Set the initial retransmit	timeout	to the specified
		     value, expressed in tenths	of a second.  May be useful
		     for fine tuning UDP mounts	over internetworks with	high
		     packet loss rates or an overloaded	server.	 Try increas-
		     ing 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 dumbtimer option should
		     be	specified when using this option to manually tune the
		     timeout interval.)

		     Alias for timeout.

	     udp     Use UDP transport.

		     Use the specified version number for NFS requests.	 See
		     the nfsv2,	nfsv3, and nfsv4 options for details.

		     Set the maximum pending write commit size to the speci-
		     fied value.  This determines the maximum amount of	pend-
		     ing write data that the NFS client	is willing to cache
		     for each file.

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

     The following command line	flags are equivalent to	-o named options and
     are supported for compatibility with older	installations.

     -2	     Same as -o	nfsv2

     -3	     Same as -o	nfsv3

     -D	     Same as -o	deadthresh

     -I	     Same as -o	readdirsize=<value>

     -L	     Same as -o	nolockd

     -N	     Same as -o	noresvport

     -P	     Use a reserved socket port	number.	 This flag is obsolete,	and
	     only retained for compatibility reasons.  (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	     Same as -o	retrycnt=<value>

     -T	     Same as -o	tcp

     -U	     Same as -o	mntudp

     -a	     Same as -o	readahead=<value>

     -b	     Same as -o	bg

     -c	     Same as -o	noconn

     -d	     Same as -o	dumbtimer

     -g	     Same as -o	maxgroups

     -i	     Same as -o	intr

     -l	     Same as -o	rdirplus

     -r	     Same as -o	rsize=<value>

     -s	     Same as -o	soft

     -t	     Same as -o	retransmit=<value>

     -w	     Same as -o	wsize=<value>

     -x	     Same as -o	retrans=<value>

     The following -o named options are	equivalent to other -o named options
     and are supported for compatibility with other operating systems (e.g.,
     Linux, Solaris, and OSX) to ease usage of autofs(5) support.

     -o	vers=2
	     Same as -o	nfsv2

     -o	vers=3
	     Same as -o	nfsv3

     -o	vers=4
	     Same as -o	nfsv4

     nmount(2),	unmount(2), nfsv4(4), fstab(5),	gssd(8), mount(8), nfsd(8),
     nfsiod(8),	showmount(8)

     Since nfsv4 performs open/lock operations that have their ordering
     strictly enforced by the server, the options intr and soft	cannot be
     safely used.  hard	nfsv4 mounts are strongly recommended.

BSD				April 13, 2017				   BSD


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