| NFSV4(4) | Device Drivers 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 and Network File System (NFS) Version 4 Minor Version 1 Protocol RFC 5661. 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 - pNFS, where I/O operations are separated from Metadata operations
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 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:
<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 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.
vfs.nfs.enable_uidtostring vfs.nfsd.enable_stringtouid
On the client, the sysctl
vfs.nfs.enable_uidtostring
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 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 set the variables in
rc.conf(5) as follows:
nfs_server_enable="YES" nfsv4_server_enable="YES"
plus
nfsuserd_enable="YES"
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.
vfs.nfsd.issue_delegationsNFSv4 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_locallocksNote 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.
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
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" <-- If name<->uid/gid mapping is being used. nfscbd_enable="YES"
are set in rc.conf(5).
Without a functioning callback path, a server will never issue Delegations to a client.
For NFSv4.0, 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).
For NFSv4.1, 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 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.
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.
| July 19, 2017 | Debian |