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

DESCRIPTION
     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
     implements 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
     uninterruptibly until the server comes back.  To modify this default be‐
     haviour, 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:

	     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.

	     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.

	     deadthresh=⟨value⟩
		     Set the “dead server threshold” to the specified number
		     of round trip timeout intervals before a “server not
		     responding” message is displayed.

	     dumbtimer
		     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.

	     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.

	     maxgroups=⟨value⟩
		     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.)

	     negnametimeo=⟨value⟩
		     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 the experimental nfs subsystem and TCP
		     transport.	 To use the experimental nfs subsystem for
		     nfsv2 and nfsv3 mounts, you must specify the ``newnfs''
		     file system type instead of ``nfs''.

	     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
		     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.

	     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.

	     nolockd
		     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.

	     principal
		     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.

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

	     port=⟨port_number⟩
		     Use specified port number for NFS requests.  The default
		     is to query the portmapper for the NFS port.

	     rdirplus
		     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
		     attribute and name caches with prefetched entries.	 Try
		     this option and see whether performance improves or
		     degrades.	Probably most useful for client to server net‐
		     work interconnects with a large bandwidth times delay
		     product.

	     readahead=⟨value⟩
		     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‐
		     uct.

	     readdirsize=⟨value⟩
		     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.

	     resvport
		     Use a reserved socket port number.	 This flag is obso‐
		     lete, 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.)

	     retrans=⟨value⟩
		     Set the retransmit timeout count for soft mounts to the
		     specified value.

	     retrycnt=⟨count⟩
		     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.

	     rsize=⟨value⟩
		     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
		     actively using a mount point.  (Use netstat(1) with the
		     -s option to see what the “fragments dropped due to
		     timeout” value is.)

	     sec=⟨flavor⟩
		     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
		     interoperability.

	     timeout=⟨value⟩
		     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 over‐
		     loaded 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 retransmit
		     rate but long response delay observed.  (Normally, the
		     dumbtimer option should be specified when using this
		     option to manually tune the timeout interval.)

	     udp     Use UDP transport.

	     wsize=⟨value⟩
		     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.

COMPATIBILITY
     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⟩

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

BUGS
     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				 July 28, 2009				   BSD
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