Installation guide

Chapter 17. Network File System (NFS) 253
This line states that any directory a user tries to access under the local /home directory (due to the
asterisk character) should result in an NFS mount on the server.domain.com system within its exported
/home file system. The mount options specify that each /home directory NFS mounts should use a
particular collection of settings. For more information on mount options, including the ones used in
this example, see Section 17.3.3.
17.3.3. Common NFS Mount Options
Beyond mounting a file system via NFS on a remote host, a number of different options may be
specified at the time of the mount that can make it easier to use. These options can be used with
manual mount commands, /etc/fstab settings, and autofs, and other mounting methods.
The following options are the most popular for NFS mounts:
• hard or soft — specifies whether the program using a file via an NFS connection should stop
and wait (hard) for the server to come back online if the host serving the exported file system is
unavailable, or if it should report an error (soft).
If you specify hard, you will not be able to terminate the process waiting for the NFS communica-
tion to resume unless you also specify the intr option.
If you specify soft, you can set an additional timeo=
value option, where value specifies
the number of seconds to pass before the error is reported.
• intr — allows NFS requests to be interrupted if the server goes down or cannot be reached.
• nolock — is occasionally required when connecting to older NFS server. To require locking, use
the lock option.
• noexec — does not permit the execution of binaries on the mounted file system. This is useful if
your Red Hat Linux system is mounting a non-Linux file system via NFS that contains binaries that
will not execute on your machine.
• nosuid — does not allow set-user-identifier or set-group-identifier bits to take effect.
• rsize=8192 and wsize=8192 — may speed up NFS communication for reads (rsize) and writes
(wsize) by setting a larger data block size, in bytes, to be transferred at one time. Be careful when
changing these values; some older Linux kernels and network cards may not work well with larger
block sizes.
• nfsvers=2 or nfsvers=3 — specify which version of the NFS protocol to use.
Many more options are listed on the mount man page, including options for mounting non-NFS file
systems.
17.4. Securing NFS
NFS works well for sharing entire file systems with a large number of known hosts in a largely
transparent manner. Many users accessing files over an NFS mount may not be aware that the file
system they are using is not local to their system. However, with ease of use comes a variety of
potential security problems.
The following points should be considered when exporting NFS file systems on a server or mounting
them on a client. Doing so will minimize NFS security risks and better protect your data.