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NFSV4(4)               FreeBSD Kernel Interfaces Manual               NFSV4(4)

     NFSv4 - NFS Version 4 Protocol

     The NFS client and server provides support for the NFSv4 specification;
     see Network File System (NFS) Version 4 Protocol RFC 3530. The protocol
     is somewhat similar to NFS Version 3, but differs in significant ways.
     It uses a single compound RPC that concatenates operations to-gether.
     Each of these operations are similar to the RPCs of NFS Version 3.  The
     operations in the compound are performed in order, until one of them
     fails (returns an error) and then the RPC terminates at that point.

     It has integrated locking support, which implies that the server is no
     longer stateless.  As such, the NFSv4 server remains in recovery mode for
     a grace period (always greater than the lease duration the server uses)
     after a reboot.  During this grace period, clients may recover state but
     not perform other open/lock state changing operations.  To provide for
     correct recovery semantics, a small file described by stablerestart(5) is
     used by the server during the recovery phase.  If this file is missing or
     empty, there is a backup copy maintained by nfsd(8) that will be used. If
     either file is missing, they will be created by the nfsd(8).  If both the
     file and the backup copy are empty, it will result in the server starting
     without providing a grace period for recovery.  Note that recovery only
     occurs when the server machine is rebooted, not when the nfsd(8) are just

     It provides several optional features not present in NFS Version 3:

           - NFS Version 4 ACLs
           - Referrals, which redirect subtrees to other servers
             (not yet implemented)
           - Delegations, which allow a client to operate on a file locally

     The NFSv4 protocol does not use a separate mount protocol and assumes
     that the server provides a single file system tree structure, rooted at
     the point in the local file system tree specified by one or more

           V4: <rootdir> [-sec=secflavors] [host(s) or net]

     line(s) in the exports(5) file.  (See exports(5) for details.)  The
     nfsd(8) allows a limited subset of operations to be performed on non-
     exported subtrees of the local file system, so that traversal of the tree
     to the exported subtrees is possible.  As such, the ``<rootdir>'' can be
     in a non-exported file system.  The exception is ZFS, which checks
     exports and, as such, all ZFS file systems below the ``<rootdir>'' must
     be exported.  However, the entire tree that is rooted at that point must
     be in local file systems that are of types that can be NFS exported.
     Since the NFSv4 file system is rooted at ``<rootdir>'', setting this to
     anything other than ``/'' will result in clients being required to use
     different mount paths for NFSv4 than for NFS Version 2 or 3.  Unlike NFS
     Version 2 and 3, Version 4 allows a client mount to span across multiple
     server file systems, although not all clients are capable of doing this.

     NFSv4 uses names for users and groups instead of numbers.  On the wire,
     they take the form:


     where ``<dns.domain>'' is not the same as the DNS domain used for host
     name lookups, but is usually set to the same string.  Most systems set
     this ``<dns.domain>'' to the domain name part of the machine's
     hostname(1) by default.  However, this can normally be overridden by a
     command line option or configuration file for the daemon used to do the
     name<->number mapping.  Under FreeBSD, the mapping daemon is called
     nfsuserd(8) and has a command line option that overrides the domain
     component of the machine's hostname.  For use of NFSv4, either client or
     server, this daemon must be running.  If this ``<dns.domain>'' is not set
     correctly or the daemon is not running, ``ls -l'' will typically report a
     lot of ``nobody'' and ``nogroup'' ownerships.

     Although uid/gid numbers are no longer used in the NFSv4 protocol, they
     will still be in the RPC authentication fields when using AUTH_SYS
     (sec=sys), which is the default.  As such, in this case both the
     user/group name and number spaces must be consistent between the client
     and server.

     However, if you run NFSv4 with RPCSEC_GSS (sec=krb5, krb5i, krb5p), only
     names and KerberosV tickets will go on the wire.

     To set up the NFS server that supports NFSv4, you will need to either set
     the variables in rc.conf(5) as follows:


     or start mountd(8) and nfsd(8) without the ``-o'' option, which would
     force use of the old server.  The nfsuserd(8) daemon must also be

     You will also need to add at least one ``V4:'' line to the exports(5)
     file for NFSv4 to work.

     If the file systems you are exporting are only being accessed via NFSv4
     there are a couple of sysctl(8) variables that you can change, which
     might improve performance.

             when set non-zero, allows the server to issue Open Delegations to
             clients.  These delegations permit the client to manipulate the
             file locally on the client.  Unfortunately, at this time, client
             use of delegations is limited, so performance gains may not be
             observed.  This can only be enabled when the file systems being
             exported to NFSv4 clients are not being accessed locally on the
             server and, if being accessed via NFS Version 2 or 3 clients,
             these clients cannot be using the NLM.

             can be set to 0 to disable acquisition of local byte range locks.
             Disabling local locking can only be done if neither local
             accesses to the exported file systems nor the NLM is operating on

     Note that Samba server access would be considered ``local access'' for
     the above discussion.

     To build a kernel with the NFS server that supports NFSv4 linked into it,

           options NFSD

     must be specified in the kernel's config(5) file.

     To do an NFSv4 mount, specify the ``nfsv4'' option on the mount_nfs(8)
     command line.  This will force use of the client that supports NFSv4 plus
     set ``tcp'' and NFSv4.

     The nfsuserd(8) must be running, as above.  Also, since an NFSv4 mount
     uses the host uuid to identify the client uniquely to the server, you
     cannot safely do an NFSv4 mount when


     is set in rc.conf(5).

     If the NFSv4 server that is being mounted on supports delegations, you
     can start the nfscbd(8) daemon to handle client side callbacks.  This
     will occur if


     are set in rc.conf(5).

     Without a functioning callback path, a server will never issue
     Delegations to a client.

     By default, the callback address will be set to the IP address acquired
     via rtalloc() in the kernel and port# 7745.  To override the default
     port#, a command line option for nfscbd(8) can be used.

     To get callbacks to work when behind a NAT gateway, a port for the
     callback service will need to be set up on the NAT gateway and then the
     address of the NAT gateway (host IP plus port#) will need to be set by
     assigning the sysctl(8) variable vfs.nfs.callback_addr to a string of the


     where the first 4 Ns are the host IP address and the last two are the
     port# in network byte order (all decimal #s in the range 0-255).

     To build a kernel with the client that supports NFSv4 linked into it, the

           options NFSCL

     must be specified in the kernel's config(5) file.

     Options can be specified for the nfsuserd(8) and nfscbd(8) daemons at
     boot time via the ``nfsuserd_flags'' and ``nfscbd_flags'' rc.conf(5)

     NFSv4 mount(s) against exported volume(s) on the same host are not
     recommended, since this can result in a hung NFS server.  It occurs when
     an nfsd thread tries to do an NFSv4 VOP_RECLAIM()/Close RPC as part of
     acquiring a new vnode.  If all other nfsd threads are blocked waiting for
     lock(s) held by this nfsd thread, then there isn't an nfsd thread to
     service the Close RPC.

     /var/db/nfs-stablerestart      NFS V4 stable restart file
     /var/db/nfs-stablerestart.bak  backup copy of the file

     stablerestart(5), mountd(8), nfscbd(8), nfsd(8), nfsdumpstate(8),
     nfsrevoke(8), nfsuserd(8)

     At this time, there is no recall of delegations for local file system
     operations.  As such, delegations should only be enabled for file systems
     that are being used solely as NFS export volumes and are not being
     accessed via local system calls nor services such as Samba.

FreeBSD 11.1-RELEASE-p4          July 1, 2013          FreeBSD 11.1-RELEASE-p4
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