Any NFS share made available by a server can be mounted using various
methods. The share can be manually mounted, using the
mount command. However, this requires that the root
user type the mount command every time the system
restarts. Two methods of configuring NFS shares to be mounted
automatically at boot time include modifying the
/etc/fstab or using the autofs
service.
9.3.1. /etc/fstab
Placing a properly formatted line in the
/etc/fstab file has the same effect as manually
mounting the exported file system. The /etc/fstab
file is read by the /etc/rc.d/init.d/netfs script
at system startup and any NFS shares listed there will be mounted.
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>
corresponds to hostname, IP address, or fully qualified domain name of
the server exporting the file system.
The
</path/of/directory>
is the path to the exported directory.
The
</local/mount/point>
specifies where on the local file system 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 file system
being mounted.
The <options> area
specifies mount options for the file system. For example, if the
options area states rw,suid, the exported file system
will be mounted read-write and the user and groupid set by the server
will be used. Note that parentheses are not to be used here. For more
mount options, see Section 9.3.3 Common NFS Mount Options.
9.3.2. autofs
One drawback to using /etc/fstab is that,
regardless of how infrequently a user may access the NFS mounted file
system, the system must dedicate resources to keep that mount in
place. This is not a problem with one or two mounts, but when the
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
file systems automatically, saving resources.
The autofs script, located in the
/etc/rc.d/init.d/ directory, 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.
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:
The <mount-point>
element of this line indicates the location of the mount on the local file
system. 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-file-system> |
The <directory>
refers to the directory within the mount point where the exported file
system should be mounted. Much like a standard
mount command, the host exporting the file system,
as well as the file system being exported, are required in the
<host>:<exported-file
system> section. To specify particular
options to be used when mounting the exported file system, place them
in the
<mount-options>
section, separated by commas. For NFS mounts that use
autofs, place -fstype=nfs in the
<mount-options>
section.
While autofs configuration files can be used for a
variety of mounts to many types of devices and file systems, 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:
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.example.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.example.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 9.3.3 Common NFS Mount Options.
9.3.3. 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 hard is specified, the user cannot
terminate the process waiting for the NFS communication to resume
unless intr option is also specified.
If soft, is specified, the user 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 the
system is mounting a non-Linux file system via NFS that contains
incompatible binaries.
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.
