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Chapter 18. Network File System (NFS) 245

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 ﬁlesystem. 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 18.3.3.

18.3.3. Common NFS Mount Options

Beyond mounting a ﬁlesystem via NFS on a remote host, a number of different options may be speci-

ﬁed at the time of the mount that can make it easier to use. These options can be utilized 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 ﬁlesystem is un-

available, 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 ﬁlesystem. This is useful if your

Red Hat Linux system is mounting a non-Linux ﬁlesystem 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 available on the mount man page, including options to be used when mounting

non-NFS ﬁlesystems.

18.4. Securing NFS

NFS works well for sharing entire ﬁlesystems with a large number of known hosts in a largely trans-

parent manner. Many users accessing ﬁles over an NFS mount may not be aware that the ﬁlesystem

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 ﬁlesystems on a server or mount-

ing them on a client. Doing so will minimize NFS security risks and better protect your data and

equipment.

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 245