NFS Services Administrator's Guide

Introduction
New Features in NFS
Chapter 126
However, UNIX systems use integers to represent users and groups
in the underlying filesystems stored on the disk. As a result, using
string identifiers requires mapping of string names to integers and
back.
The nfsmapid daemon is used to map the owner and owner_group
identification attributes with the local user identification (UID) and
group identification (GID) numbers, which are used by both the
NFSv4 server and the NFSv4 client.
On the NFS client, the nfsmapid daemon maps a numeric UID or a
numeric GID to a string representation. On the NFS server, it maps
a string representation to a numeric UID or a numeric GID.
For example, user casey with UID 121212 on an NFSv4 client whose
fully qualified name is system.anydomain.com is mapped to
[e-mail]. The NFS client sends the string
representation, [e-mail], to the NFS server. The NFS
server maps the string representation, [e-mail], to the
unique ID 121212.
The nfsmapid daemon uses the user and group entries in the
/etc/nsswitch.conf file, to determine which name service to use
while converting strings and numerical values and back.
For information on how to configure the nfsmapid daemon, see
nfsmapid (1M).
• File Locking
File locking support is integrated with the NFSv4 protocol. NFSv4
introduces leases for lock management.
When a server grants a lock to control the access of a file for a
specific period of time, it is called a lease. During the lease period,
the server cannot grant conflicting access to another client.
The lock lease interval can accept values higher than the cache
consistency leases. As a result, the client requires only a smaller
number of refreshes. The lease ensures that the client does not lose
the locking state.
If a client refreshes a lock, all locks held by the client with that
server are validated. This reduces the number of lease refreshes by
the client from one per lock to one per client for a specific lease.