Use the mount command to mount a shared
NFS directory from another machine:
mount shadowman.example.com:/misc/export /misc/local
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Warning |
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The mount point directory on the local machine (/misc/local in the above example) must exist before
this command can be executed.
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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
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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
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Next, add the following line to /etc/auto.misc:
myproject -rw,soft,intr,rsize=8192,wsize=8192 penguin.example.net:/proj52
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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.
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Note |
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The directory /misc must exist on the
local file system. There should be no subdirectories in /misc on the local file system.
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To start the autofs service, at a shell prompt, type the
following command:
/sbin/service autofs restart
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To view the active mount points, type the following command at a
shell prompt:
/sbin/service autofs status
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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
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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
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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
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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
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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:
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Improved connection durability, thus less NFS stale file handles messages.
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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.
