bionic (4) nfsv4.4freebsd.gz

NAME

     NFSv4 — NFS Version 4 Protocol

DESCRIPTION

     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 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

     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:

           <user>@<dns.domain>

     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.

SERVER SETUP

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

           nfs_server_enable="YES"
           nfsv4_server_enable="YES"
           nfsuserd_enable="YES"

     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 running.

     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.

     vfs.nfsd.issue_delegations
             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.

     vfs.nfsd.enable_locallocks
             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 them.

     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, the

           options NFSD

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

CLIENT MOUNTS

     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

           hostid_enable="NO"

     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"
           nfscbd_enable="YES"

     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 form:

     N.N.N.N.N.N

     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 option

           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) variables.

     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.

FILES

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

SEE ALSO

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

BUGS

     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.