Command Section
MOUNT_NFS(8)            FreeBSD 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
     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
     behaviour 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
     behaviour, see the intr and soft options.

     The options are:

     -o      Options are specified with a -o flag followed by a comma
             separated 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
                     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
                     limits 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
                     estimated timeout interval is too short.

             fg      Same as not specifying bg.

                     This option can be used with the KerberosV security
                     flavors for NFSv4 mounts to specify the
                     ``service-principal-name'' of a host-based entry in the
                     default 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
                     operations 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
                     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.

             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
                     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.

             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
                     implemented 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
                     improve 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
                     option 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
                     applications 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
                     modifying 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
                     overrides the default, which will be ``[email protected]<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
                     Operation get more attributes.  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

                     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

                     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
                     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.)

                     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
                     actively 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
                     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.)

                     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
                     specified value.  This determines the maximum amount of
                     pending 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.

FreeBSD 11.1-RELEASE-p4         April 13, 2017         FreeBSD 11.1-RELEASE-p4
Command Section