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NFS Server

Network File System (NFS)

  •  A Network File System (NFS) allows remote hosts to mount file systems over a network and interact with those file systems as though they are mounted locally. This enables system administrators to consolidate resources onto centralized servers on the network.
  • All versions of NFS can use Transmission Control Protocol (TCP) running over an IP network, with NFSv4 requiring it. NFSv2 and NFSv3 can use the User Datagram Protocol (UDP) running over an IP network to provide a stateless network connection between the client and server.
  • The NFS server sends the client a file handle after the client is authorized to access the shared volume. This file handle is an opaque object stored on the server’s side and is passed along with RPC requests from the client. The NFS server can be restarted without affecting the clients and the cookie remains intact. However, because UDP is stateless, if the server goes down unexpectedly, UDP clients continue to saturate the network with requests for the server. For this reason, TCP is the preferred protocol when connecting to an NFS server.
  • After the client is granted access by TCP wrappers, the NFS server refers to its configuration file,/etc/exports, to determine whether the client is allowed to access any of the exported file systems. Once access is granted, all file and directory operations are available to the user.

Required Services

 Red Hat Enterprise Linux uses a combination of kernel-level support and daemon processes to provide NFS file sharing. All NFS versions rely on Remote Procedure Calls (RPC) between clients and servers. RPC services under Linux are controlled by the portmap service. To share or mount NFS file systems, the following services work together, depending on which version of NFS is implemented:
  • nfs — (/sbin/service nfs start) starts the NFS server and the appropriate RPC processes to service requests for shared NFS file systems.
  • nfslock — (/sbin/service nfslock start) is a mandatory service that starts the appropriate RPC processes to allow NFS clients to lock files on the server.
  • portmap — accepts port reservations from local RPC services. These ports are then made available (or advertised) so the corresponding remote RPC services access them. portmap responds to requests for RPC services and sets up connections to the requested RPC service. This is not used with NFSv4.

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.

The /etc/fstab file is referenced by the netfs service at boot time, so lines referencing NFS shares have the same effect as manually typing the mount command during the boot process.

A sample /etc/fstab line to mount an NFS export looks like the following example:

<server>:</remote/export> </local/directory> <nfs-type> <options> 0 0
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