NFS Services Administrator's Guide

Configuring and Administering NFS
Configuring and Administering an NFS Client
Chapter 2 53
Several NFS mount options allow you to change the length of time file
and directory attributes remain cached on the NFS client. By default, an
NFS client caches certain attributes of files and directories, like their
ownership, size, and modification time. If a user on an NFS client is
making a series of changes to a file, the changes to the file’s attributes
are cached and modified locally on the client, and finally, the resulting
attributes are sent to the server.
Table 2-3 NFS Caching Options
noac
(default: not
specified)
If specified, this option prevents the NFS client from
caching attributes for the mounted directory.
Specify noac for a directory that will be used frequently
by many NFS clients. The noac option ensures that the
file and directory attributes on the server are up to date,
because no changes are cached on the clients. However,
if many NFS clients using the same NFS server all
disable attribute caching, the server may become
overloaded with attribute requests and updates. You can
also use the actimeo option to set all the caching
timeouts to a small number of seconds, like 1 or 3.
If you specify noac, do not specify the other caching
options.
nocto
(default: not
specified)
If specified, this option suppresses fresh attributes when
opening a file.
Specify nocto for a file or directory that never changes,
to decrease the load on your network.
acdirmax=n
(default=60)
The maximum number of seconds a directory’s
attributes are cached on the NFS client. When this
timeout period expires, the client flushes its attribute
cache, and if the attributes have changed, the client
sends them to the NFS server.
For a directory that rarely changes or that is owned and
modified by only one user, like a user’s home directory,
you can decrease the load on your network by setting
acdirmax=120 or higher.