NAME¶
nfsv4 —
NFS Version 4 Protocol
SYNOPSIS¶
experimental client and server with NFSv4 support
DESCRIPTION¶
The experimental nfs client and server provides support for the NFSv4
specification; see
Network File System (NFS) Version 4
Protocol \*(tNRFC\*(sP 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, 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-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. 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 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 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.
SERVER SETUP¶
To set up the experimental nfs server that supports
nfsv4 you
will need to either build a kernel with:
and not
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
nfs_server_enable="YES"
nfsv4_server_enable="YES"
nfsuserd_enable="YES"
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
/var/db/nfs-stablerestart
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
recommended.
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.newnfs.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.newnfs.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 experimental
nfsv4 linked into it,
the
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
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
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.newnfs.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 experimental
nfsv4 client linked
into it, the option
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.
FILES¶
- /var/db/nfs-stablerestart
- NFS V4 stable restart 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 soley as NFS export volumes and are not being accessed via
local system calls nor services such as Samba.
