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Version 4
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This definition of the NFS version 4 protocol replaces or obsoletes
the definition present in [RFC3010]. While portions of the two
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The NFS version 4 protocol is a further revision of the NFS protocol
defined already by versions ...
... filesystems, simplicity, and good performance. The NFS version 4
revision has the following goals:
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... supporting the RPCSEC_GSS protocol. Additionally, the NFS version
4 protocol provides a mechanism to allow clients and servers the
ability to negotiate security ...
... context for the reader, the major features of
NFS version 4 protocol will be reviewed in brief. This will be done
to provide an appropriate context for both the reader who is familiar
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... RPC) mechanisms used for the NFS
version 4 protocol are those defined in [RFC1831] and [RFC1832]. To
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... integrity, and privacy to the NFS version 4 protocol.
Kerberos V5 will be used as described in [RFC1964 ...
... server public key by the NFS version 4 protocol. With the use of
RPCSEC_GSS, other mechanisms may also be specified and used for NFS ...
... in-band security negotiation, the NFS version 4 protocol
has added a new operation which provides the client a method ...
... protocol is the introduction of the COMPOUND procedure. For the NFS
version 4 protocol, there are two RPC procedures, NULL and COMPOUND.
The COMPOUND procedure is defined in terms of operations and these
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The NFS version 4 protocol continues to have the client refer to a
file or directory at the server by a "filehandle". The COMPOUND
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The general filesystem model used for the NFS version 4 protocol is
the same as previous versions. The server filesystem is hierarchical
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The NFS version 4 protocol does not require a separate protocol to
provide for the initial mapping between path name and filehandle.
Instead of using the older MOUNT protocol for this mapping, the
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meet. For the NFS version 4 protocol, this requirement has been
relaxed by introducing another type of filehandle, volatile. With
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The NFS version 4 protocol introduces three classes of filesystem or
file attributes. Like the additional filehandle type, the
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The NFS version 4 protocol introduces OPEN and CLOSE operations. The
OPEN operation provides a single point where file lookup, creation,
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The file, attribute, and directory caching for the NFS version 4
protocol is similar to previous versions. Attributes and directory
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The major addition to NFS version 4 in the area of caching is the
ability of the server to delegate certain responsibilities to the
client ...
... Stable Storage
NFS version 4 servers must be able to recover without data
loss from multiple power failures (including cascading
power failures, that is, several power failures in quick
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... syntax and semantics to describe the data types of the NFS
version 4 protocol are defined in the XDR [RFC1832] and RPC ...
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Where an NFS version 4 implementation supports operation over the IP
network protocol, the supported transports between NFS ...
... interoperability, an NFS version 4 implementation MUST support
operation over the TCP transport protocol ...
... authentication
model for NFS version 4 has moved from machine-based to principal-
based. However, this modification of the authentication ...
... number of expected client machines. It is intended that NFS version
4 will not modify this connection management model. NFS ...
... connection management model. NFS version 4
clients that violate this assumption can expect scaling issues on the
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... TCP, the NFS version 4 server MUST NOT silently drop the request,
except if the transport connection has been broken. Given such a
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... transport connection has been broken. Given such a
contract between NFS version 4 clients and servers, clients MUST NOT
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... transport connection
break will eventually be indicated to the NFS version 4 client. The
client ...
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With the NFS version 4 server potentially offering multiple security
mechanisms, the client needs a method ...
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Based on the assumption that each NFS version 4 client and server
must support a minimum set of security ...
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Therefore, the NFS version 4 protocol will not use an ancillary
protocol for translation from string based path names to a
filehandle. Two special filehandles will be used as starting ...
... semantics. This type of filehandle
is termed "persistent" in NFS Version 4. The semantics of a
persistent filehandle remain the same as before. A new type of
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... persistent filehandle remain the same as before. A new type of
filehandle introduced in NFS Version 4 is the "volatile" filehandle,
which attempts to accommodate certain server environments.
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... recommended, and named. Both mandatory and recommended attributes
are supported in the NFS version 4 protocol by a specific and well-
defined encoding and are identified by number. They are requested by
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These MUST be supported by every NFS version 4 client and server in
order to ensure a minimum level of interoperability ...
... These attributes are understood well enough to warrant support in the
NFS version 4 protocol. However, they may not be supported on all
clients and servers. A client ...
... encoding in the NFS
Version 4 protocol but are accessed by string names rather than
numbers and correspond to an uninterpreted stream of bytes which are
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... ACLs. For example, the enforcement for
NFS version 4 access may be different from the enforcement for local
access, and both may be different from the enforcement for access
through other protocols such as SMB. So it may be useful for a
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While the NFS version 4 client could simply fabricate a fileid
corresponding to what mounted_on_fileid provides (and if the server
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... With the use of the recommended attribute "fs_locations", the NFS
version 4 server has a method of providing filesystem migration or
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NFS version 4 servers avoid this name space inconsistency by
presenting all the exports within the framework ...
... top level names. NFS
version 4 servers for these platforms can construct a pseudo file
system above these root ...
... CREATE, ACCESS) need to be replaced. The NFS version 4 protocol has
an OPEN operation that subsumes the NFS version 3 ...
... where there is no local disk and all file access is from an NFS
version 4 server.
o The string should be different for each server network ...
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o For a user level NFS version 4 client, it should contain
additional information to distinguish the client ...
... - The timestamp of when the NFS version 4 software was first
installed on the client (though this is subject ...
... stored in a file, because the file might only be accessible
over NFS version 4).
- A true random number ...
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Thus, the NFS version 4 LOCK operation does not need to distinguish
between advisory and mandatory record locks. It is the NFS version 4 ...
... version 4 LOCK operation does not need to distinguish
between advisory and mandatory record locks. It is the NFS version 4
server's processing of the READ and WRITE operations that introduces
the distinction.
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... Some clients require the support of blocking locks. The NFS version
4 protocol must not rely on a callback mechanism and therefore is
unable to notify a client when a previously denied lock has been
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... old server is left to the server implementations. It is not
specified by the NFS version 4 protocol.
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The NFS version 4 protocol uses many techniques similar to those that
have been used in previous protocol versions. The NFS ...
... have been used in previous protocol versions. The NFS version 4
protocol does not provide distributed cache coherence. However, it
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In addition, the NFS version 4 protocol introduces a delegation
mechanism which allows many decisions normally made by the server ...
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The NFS version 4 protocol provides more aggressive caching
strategies with the following design goals:
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... delegation reclaim reconciles
three principles of the NFS version 4 protocol:
o Upon reclaim, a client ...
... Share reservations and record locks are the facilities the NFS
version 4 protocol provides to allow applications to coordinate
access by providing mutual exclusion facilities. The NFS version 4 ...
... version 4 protocol provides to allow applications to coordinate
access by providing mutual exclusion facilities. The NFS version 4
protocol's data caching must be implemented such that it does not
invalidate the assumptions that those using these facilities depend
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... In order to avoid invalidating the sharing assumptions that
applications rely on, NFS version 4 clients should not provide cached
data to applications or modify it on behalf of an application when it
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... will work on a local filesystem. However, they may not work with the
NFS version 4 protocol unless clients refrain from data caching.
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In the NFS version 4 protocol, there is now the possibility to have
significant deviations from a "one filehandle per object" model
because a filehandle may be constructed on the basis of the object's
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... By providing a method to differentiate filehandles, the NFS version 4
protocol alleviates a potential functional regression in comparison
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... For the purposes of data caching, the following steps allow an NFS
version 4 client to determine whether two distinct filehandles denote
the same server side ...
... NFS protocol that can evolve as the
need arises, the NFS version 4 protocol contains the rules and
framework to allow for future minor changes or versioning.
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... version zero of the NFS
version 4 protocol is represented by this RFC. The COMPOUND
procedure will support the encoding of the minor version ...
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The primary issue in which NFS version 4 needs to deal with
internationalization, or I18N, is with respect to file names and
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... There are three UTF-8 string types defined for NFS version 4:
utf8str_cs, utf8str_cis, and utf8str_mixed. Separate profiles are
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... Stringprep discusses Unicode characters, whereas NFS version 4
renders UTF-8 characters. Since there is a one to one mapping from
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... Every use of the utf8str_cs type definition in the NFS version 4
protocol specification follows the profile ...
... UTF-8 characters.
Its primary use in NFS Version 4 is for naming components and
pathnames. Components and pathnames are stored on the server's
filesystem. Two valid ...
... profile. If the strings are two names
inside a directory, the NFS version 4 server will need to either:
o disallow the creation of a second name if it's post processed form
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... case-insensitive comparisons. However, if
the NFS version 4 file server supports the case_insensitive
filesystem attribute, and if case_insensitive is true, the NFS
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... filesystem attribute, and if case_insensitive is true, the NFS
version 4 server MUST use Table B.2 (in addition to Table B1) when
processing utf8str_cs strings, and the NFS version 4 ...
... version 4 server MUST use Table B.2 (in addition to Table B1) when
processing utf8str_cs strings, and the NFS version 4 client MUST
assume Table B.2 (in addition to Table B.1) are being used.
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... If the case_preserving attribute is present and set to false, then
the NFS version 4 server MUST use table B.2 to map case when
processing utf8str_cs strings. Whether the server maps from lower to
upper case or the upper to lower case is an implementation
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... Every use of the utf8str_cis type definition in the NFS version 4
protocol specification follows the profile ...
... Every use of the utf8str_mixed type definition in the NFS version 4
protocol specification follows the profile ...
... is fully qualified domain name. Its primary use in NFS Version 4 is
for naming principals identified in an Access Control Entry ...
... NFS4ERR_SERVERFAULT An error occurred on the server which does not
map to any of the legal NFS version 4 protocol
error values. The client should translate this
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... signaling and is constructed in a similar fashion as the NFS version
4 program. The procedures CB_NULL and CB_COMPOUND are defined in the
same way as NULL and COMPOUND are within the NFS program. The
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NFS version 4 operations that modify the filesystem are synchronous.
When an operation is successfully completed at the server, the client ...
... whether an operation was allowed was to try it and see if it
succeeded or failed. Using the ACCESS operation in the NFS version 4
protocol, the client can ask the server to indicate whether or not
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... semantics to
the names "." and "..". NFS version 4 assigns no special semantics
to these names. The LOOKUPP operator must be used to lookup ...
... the server must return NFS4ERR_ACCESS. Note that since the NFS
version 4 protocol does not impose any requirement that READs and
WRITEs issued for an open file have the same credentials ...
... open_owner4s or stop using them for indefinite periods of time. The
latter situation is why the NFS version 4 protocol does not have an
explicit operation to exit an open_owner4: such an operation is of no
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... RFC2055], [RFC2224]. The intent for NFS version 4 is that the
public filehandle (represented by the PUTPUBFH operation) be used as
a method ...
... discussion of the functionality. With NFS version 4, that type of
specification is not directly available in the LOOKUP operation. The
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... reason for this is because the component separators needed to specify
absolute vs. relative are not allowed in NFS version 4. Therefore,
the client ...
... namespace
has been made available. These same warnings apply to NFS version 4.
It is likely, therefore that because of server implementation
details, an NFS ...
... lookup may
behave differently than an NFS version 4 absolute resolution.
There is a form of security negotiation ...
... method is not available with NFS version 4 as filehandles are not
overloaded with special meaning and therefore do not provide the same
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... file type. The implementor of an NFS version 4
client's entry points from the unlink() and rmdir() system calls
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... to compromise this function, as would the corresponding delay in the
NFS version 4 emulation. Therefore, NFS version 4 servers should
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... NFS version 4 emulation. Therefore, NFS version 4 servers should
take care to avoid such delays, to the degree possible, when
executing such a request.
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... consistent during a single instance of the NFS version 4 protocol
service and must be unique between instances of the NFS ...
... service and must be unique between instances of the NFS version 4
protocol server, where uncommitted data may be lost.
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... client to detect different
instances of an NFS version 4 protocol server over which cached,
uncommitted data may be lost. In the most likely case, the verifier ...
... and/or reduction of CPU utilization, users of NFS version 4
implementations may choose to not use security mechanisms that enable
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The NFS version 4 protocol provides for the association of named
attributes to files. The name space ...
... registration of
NFS version 4 named attributes. Registration will be achieved
through the publication of an Informational RFC and will require not
...
... the corresponding r_addr field of a clientaddr4 structure. The NFS
version 4 protocol depends on the syntax and semantics of these
...
... Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame, C., Eisler, M. and D. Noveck, "NFS version 4 Protocol", RFC 3010(-> 3530prop), December 2000. ...