Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
NFSV4(4)		 BSD Kernel Interfaces Manual		      NFSV4(4)

     nfsv4 -- NFS Version 4 Protocol

     experimental client and server with NFSv4 support

     The experimental 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 signif-
     icant ways.  It uses a single Compound RPC	that concatenates operations
     to-gether.	 Each of these operations are similar to the RPCs of NFS Ver-
     sion 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

     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,
     the server	will not start.	 If this file is lost, it should be recovered
     from backups, since creating an empty stablerestart(5) file 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 restarted.

     It	provides several optional features not 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-ex-
     ported 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.  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.  On	FreeBSD, the mapping daemon is called
     nfsuserd(8) and has a command line	option that overrides the domain com-
     ponent 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 running 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 experimental	nfs server that	supports nfsv4 you will	need
     to	either build a kernel with:

	   options NFSD
     and not
	   options NFSSERVER

     or	start mountd(8)	and nfsd(8) with the ``-e'' option to force use	of the
     experimental server.  The nfsuserd(8) daemon must also be running.	 This
     will occur	if


     are set in	rc.conf(5).

     You will also need	to add at least	one ``V4:'' line to the	exports(5)
     file and, before starting the server for the first	time, create an	empty


     file.  The	command

	   install -o root -g wheel -m 600 /dev/null /var/db/nfs-stablerestart

     executed as ``su''	should suffice.	 This can only be done when the	server
     is	not running and	there are no nfsv4 file	system mounts against the
     server.  If this file is lost during a crash, recovery from backups is

     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 ac-
	     cesses 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	experimental nfsv4 linked into it, the

	   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 experimental client plus	set
     ``tcp'' and nfsv4.

     The nfsuserd(8) must be running, as above.	 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 Delega-
     tions 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	call-
     back service will need to be set up on the	NAT gateway and	then the ad-
     dress of the NAT gateway (host IP plus port#) will	need to	be set by as-
     signing the sysctl(8) variable vfs.newnfs.callback_addr to	a string of
     the form:


     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	experimental nfsv4 client 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)

     /var/db/nfs-stablerestart	NFS V4 stable restart file

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

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

BSD				April 30, 2009				   BSD


Want to link to this manual page? Use this URL:

home | help