Use the mount command to mount a shared NFS directory
from another machine:
mount shadowman.example.com:/misc/export /misc/local |
 | Warning |
|---|
| | The mount point directory on the local machine
(/misc/local in the above example) must exist
before this command can be executed. |
In this command, shadowman.example.com is the
hostname of the NFS file server, /misc/export is the
directory that shadowman is exporting, and
/misc/local is the location to mount the file system
on the local machine. After the mount command runs
(and if the client has proper permissions from the
shadowman.example.com NFS server) the client user
can execute the command ls /misc/local to display a
listing of the files in /misc/export on
shadowman.example.com.
An alternate way to mount an NFS share from another machine is to add
a line to the /etc/fstab file. The line must
state the hostname of the NFS server, the directory on the server
being exported, and the directory on the local machine where the NFS
share is to be mounted. You must be root to modify the
/etc/fstab file.
The general syntax for the line in /etc/fstab is
as follows:
server:/usr/local/pub /pub nfs rsize=8192,wsize=8192,timeo=14,intr |
The mount point /pub must exist on the client
machine before this command can be executed. After adding this line
to /etc/fstab on the client system, type the
command mount /pub at a shell prompt, and the
mount point /pub is mounted from the server.
A third option for mounting an NFS share is the use of the autofs
service. Autofs uses the automount daemon to manage your mount points
by only mounting them dynamically when they are accessed.
Autofs consults the master map configuration file
/etc/auto.master to determine which mount points
are defined. It then starts an automount process with the appropriate
parameters for each mount point. Each line in the master map defines a
mount point and a separate map file that defines the file systems to
be mounted under this mount point. For example, the
/etc/auto.misc file might define mount points in
the /misc directory; this relationship would be
defined in the /etc/auto.master file.
Each entry in auto.master has three fields. The
first field is the mount point. The second field is the location of
the map file, and the third field is optional. The third field can
contain information such as a timeout value.
For example, to mount the directory /proj52 on
the remote machine penguin.example.net at the mount point
/misc/myproject on your machine, add the following
line to auto.master:
/misc /etc/auto.misc --timeout 60 |
Next, add the following line to /etc/auto.misc:
myproject -rw,soft,intr,rsize=8192,wsize=8192 penguin.example.net:/proj52 |
The first field in /etc/auto.misc is the name of
the /misc subdirectory. This directory is created
dynamically by automount. It should not actually exist on the
client machine. The second field contains mount options such as rw
for read and write access. The third field is the location of the NFS
export including the hostname and directory.
 | Note |
|---|
| | The directory /misc must exist on the local
file system. There should be no subdirectories in
/misc on the local file system.
|
To start the autofs service, at a shell prompt, type the following
command:
/sbin/service autofs restart |
To view the active mount points, type the following command at a shell
prompt:
/sbin/service autofs status |
If you modify the /etc/auto.master configuration
file while autofs is running, you must tell the automount daemon(s)
to reload by typing the following command at a shell prompt:
/sbin/service autofs reload |
To learn how to configure autofs to start at boot time, and for
information on managing services, refer to Chapter 20 Controlling Access to Services.
The default transport protocol for NFSv4 is TCP; however, the Red Hat Enterprise Linux
4 kernel includes support for NFS over UDP. To use NFS over
UDP, include the -o udp option to
mount when mounting the NFS-exported file system on
the client system.
There are three ways to configure an NFS file system export. On demand
via the command line (client side), automatically via the
/etc/fstab file (client side), and automatically
via autofs configuration files, such as
/etc/auto.master and
/etc/auto.misc (server side with NIS).
For example, on demand via the command line (client side):
mount -o udp shadowman.example.com:/misc/export /misc/local |
When the NFS mount is specified in /etc/fstab
(client side):
server:/usr/local/pub /pub nfs rsize=8192,wsize=8192,timeo=14,intr,udp |
When the NFS mount is specified in an autofs configuration file for a NIS server,
available for NIS enabled workstations:
myproject -rw,soft,intr,rsize=8192,wsize=8192,udp penguin.example.net:/proj52 |
Since the default is TCP, if the -o udp option is not
specified, the NFS-exported file system is accessed via TCP.
The advantages of using TCP include the following:
Improved connection durability, thus less NFS
stale file handles messages.
Performance gain on heavily loaded networks because TCP
acknowledges every packet, unlike UDP which only acknowledges
completion.
TCP has better congestion control than UDP (which has none).
On a very congested network, UDP packets are the first packets
that are dropped. This means that if NFS is writing data (in 8K
chunks) all of that 8K must be retransmitted over UDP. Because of
TCP's reliability, only parts of that 8K data are transmitted at a
time.
Error detection. When a TCP connection breaks (due to the
server being unavailable) the client stops sending data and
restarts the connection process once the server becomes available.
With UDP, since it's connection-less, the client continues to
pound the network with data until the server reestablishes a
connection.
The main disadvantage is that there is a very small performance hit
due to the overhead associated with the TCP protocol.
The Red Hat Enterprise Linux 4 kernel provides ACL support for the ext3 file
system and ext3 file systems mounted with the NFS or Samba
protocols. Thus, if an ext3 file system has ACLs enabled for it and is
NFS exported, and if the NFS client can read ACLs, they are used by the
NFS client as well.
