| Red Hat Linux 7.3: The Official Red Hat Linux Reference Guide | ||
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Any NFS share made available by a server can be mounted using various methods. Of course, the share can be manually mounted, using themount command, to acquire the exported filesystem at a particular mount point. However, this requires that the root user type the mount command every time the system restarts. In addition, the root user must remember to unmount the filesystem when shutting down the machine. Two methods of configuring NFS mounts include modifying the /etc/fstab or utilizing the autofs service.
Placing a properly formatted line in the /etc/fstab file has the same effect as manually mounting the exported filesystem. The /etc/fstab file is read by the /etc/rc.d/init.d/netfs script at system startup. The proper filesystem mounts, including NFS, are put into place.
A sample /etc/fstab line to mount an NFS export looks like the following:
<server>:</path/of/dir> </local/mnt/point> nfs <options> 0 0 |
The <server-host> relates to the hostname, IP address, or fully qualified domain name of the server exporting the filesystem. The </path/to/shared/directory> tells the server what export to mount. The </local/mount/point> specifies where on the local filesystem to mount the exported directory. This mount point must exist before /etc/fstab is read or the mount will fail. The nfs option specifies the type of filesystem being mounted.
The <options> area specifies how the filesystem is to be mounted. For example, if the options area states rw,suid on a particular mount, the exported filesystem will be mounted read-write and the user and group ID set by the server will be used. Note, parentheses are not to be used here. For more mount options, see the Section called Common NFS Mount Options.
One drawback to using /etc/fstab is that, regardless of how much you use that mounted filesystem, your system must dedicate resources to keep that mount in place. This is not a problem with one or two mounts, but when your system is maintaining mounts to a dozen systems at one time, overall system performance can suffer. An alternative to /etc/fstab is to use the kernel-based automount utility, which will mount and unmount NFS filesystems automatically, saving resources.
The autofs script, located in /etc/rc.d/init.d, is used to control automount through the /etc/auto.master primary configuration file. While automount can be specified on the command line, it is more convenient to specify the mount points, hostname, exported directory, and options in a set of files rather than typing them all by hand. By running autofs as a service that starts and stops in designated runlevels, the mount configurations in the various files can be automatically implemented. In order to use autofs, you must have the autofs RPM installed on your system.
The autofs configuration files are arranged in a parent-child relationship. A main configuration file (/etc/auto.master) refers mount points on your system that are linked to a particular map type, which take the form of other configuration files, programs, NIS maps, and other less common mount methods. The auto.master file contains lines referring to each of these mount points, organized like this:
<mount-point> <map-type> |
The <mount-point> indicates where the device or exported filesystem should mount on your local filesystem. The <map-type> relates to the way in which the mount point will be mounted. The most common method for auto mounting NFS exports is to use a file as the map type for the particular mount point. The map file, usually named auto.<mount-point>, where <mount-point> is the mount point designated in auto.master, contains lines that look like this:
<directory> <mount-options> <host>:<exported-filesystem> |
The <directory> refers to the directory within the mount point where the exported filesystem should be mounted. Much like a standard mount command, the host exporting the filesystem, as well as the filesystem being exported, are required in the <host>:<exported-filesystem> section. To specify particular options to be used when mounting the exported filesystem, place them in the <mount-options> section, separated by commas. For NFS mounts that use autofs, you should definitely place -fstype=nfs in the <mount-options> section, at a minimum.
While autofs configuration files can be used for a variety of mounts to many types of devices and filesystems, they are particularly useful in creating NFS mounts. For example, some organizations store a user's /home directory on a central server via an NFS share. Then, they configure the auto.master file on each of the workstations to point to an auto.home file containing the specifics for how to mount the /home directory via NFS. This allows the user to access personal data and configuration files in their /home directory by logging in anywhere on the internal network. The auto.master file in this situation would look similar to this:
/home /etc/auto.home |
This sets up the /home mount point on the local system to be configured by the /etc/auto.home file, which may look similar to this:
* -fstype=nfs,soft,intr,rsize=8192,wsize=8192,nosuid server.domain.com:/home/& |
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 the Section called Common NFS Mount Options.
Beyond mounting a filesystem 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 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 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 communication 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.