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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 7530,	Network	File
     System (NFS) Version 4 Minor Version 1 Protocol RFC 5661, Network File
     System (NFS) Version 4 Minor Version 2 Protocol RFC 7862, File System
     Extended Attributes in NFSv4 RFC 8276 and Parallel	NFS (pNFS) Flexible
     File Layout RFC 8435.  The	protocol is somewhat similar to	NFS Version 3,
     but differs in significant	ways.  It uses a single	compound RPC that con-
     catenates 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	recov-
     ery only occurs when the server machine is	rebooted, not when the nfsd(8)
     are just restarted.

     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
	   - pNFS, where I/O operations	are separated from Metadata operations
	   And for NFSv4.2 only
	   - User namespace extended attributes
	   - lseek(SEEK_DATA/SEEK_HOLE)
	   - File copying done locally on the server for copy_file_range(2)
	   - posix_fallocate(2)

     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.  The exception is ZFS, which checks	ex-
     ports 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 any-
     thing other than ``/'' will result	in clients being required to use dif-
     ferent 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	strings	for users and groups instead of	numbers.  On the wire,
     these strings can either have the numbers in the string or	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 com-
     ponent of the machine's hostname.	For use	of this	form of	string on
     NFSv4, either client or server, this daemon must be running.

     The form where the	numbers	are in the strings can only be used for
     AUTH_SYS.	To configure your systems this way, the	nfsuserd(8) daemon
     does not need to be running on the	server,	but the	following sysctls need
     to	be set to 1 on the server.


     On	the client, the	sysctl


     must be set to 1 and the nfsuserd(8) daemon does not need to be running.

     If	these strings are not configured correctly, ``ls -l'' will typically
     report a lot of ``nobody''	and ``nogroup''	ownerships.

     Although uid/gid numbers are no longer used in the	NFSv4 protocol except
     optionally	in the above strings, they will	still be in the	RPC authenti-
     cation 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 set	the
     variables in rc.conf(5) as	follows:




     if	the server is using the	``<user>@<domain>'' form of user/group strings
     or	is using the ``-manage-gids'' option for nfsuserd(8).

     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 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	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 if	name<->uid/gid mapping is being	used,
     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

	   nfsuserd_enable="YES"   <-- If name<->uid/gid mapping is being used.

     are set in	rc.conf(5).

     Without a functioning callback path, a server will	never issue Delega-
     tions to a	client.

     For NFSv4.0, by default, the callback address will	be set to the IP ad-
     dress 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.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).

     For NFSv4.1 and NFSv4.2, the callback path	(called	a backchannel) uses
     the same TCP connection as	the mount, so none of the above	applies	and
     should work through gateways without any issues.

     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	recom-
     mended, 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 ac-
     quiring 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 ser-
     vice 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 op-
     erations.	As such, delegations should only be enabled for	file systems
     that are being used solely	as NFS export volumes and are not being	ac-
     cessed via	local system calls nor services	such as	Samba.

FreeBSD	13.0		       December	20, 2019		  FreeBSD 13.0


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