This post will make some comparisons between NFSv4 and NFSv3, and introduce how to migrate from NFSv3 to NFSv4.

As we all aware, NFSv4 is not just a simple protocol evolution of NFSv3. It has been fully redesigned to overcome the limitations of its predecessors. 

Comparison Between NFSv3 and NFSv4

1. Transport protocols

For NFSv3, the MOUNT service is normally supported over the TCP and UDP protocols.
For NFSv4, only the TCP protocol is supported.
NFS v4 is designed for internet use. One unique network port is used on NFSv4. This predetermined port is fixed. The default is port 2049. Using NFS v4 through firewalls is easier than with earlier NFS versions.

2. Locking operation

NFS v3 protocol is stateless, so an additional Network Lock Manager (NLM) protocol, an auxiliary protocol for file locking, is required to support locking of NFS-mounted files READ/WRITE. Also NLM is stateful in that the server LOCKED keeps track of locks.

NFSv4 is stateful. Locking operations(open/read/write/lock/locku/close) are part of the protocol proper. NLM is not used by NFSv4.

3. Required Services

NFSv3 relies on Remote Procedure Calls (RPC) to encode and decode requests  between clients and servers. NFSv3 depends on portmapper, rpc.mountd, rpc.lockd, rpc.statd.

NFSv4 has no interaction with portmapper, rpc.mountd, rpc.lockd, and rpc.statd, since protocol support has been incorporated into the v4 protocol. NFSv4 listens on “well-known” TCP port (2049) which eliminates the need for the portmapper interaction. The mounting and locking protocols have been incorpated into the V4 protocol which eliminates the need for interaction with rpc.mountd and rpc.lockd.

4. Security

NFS v3 supports export/mount. Thus the host makes the mount request, not a user of the file system.

With NFSv4, the mandatory security mechanisms are oriented towards authenticating individual users, e.g. by configuring the Kerberos version 5 GSS-API or other security mechanism. Full Story

Stale file handles occur when a file or directory was held open by an NFS client, and then was either removed, renamed, or replaced.

NFS-filesystems that are mounted read-write or that contain executable files should always be mounted with the “hard” option.

Normally an application is not aware of where the data (files) it is accessing is located – it only knows the pathname.  The data could be located locally in an UFS or VxFS or <whatever> filesystem, or it could be located on an NFS filesystem.  The application doesn’t care where the data is located (that’s the kernel’s job) and accesses the data by standard C-function calls such as open(), read(), write(), close(), etc.
Generally, the “normal” application usually only handles those return-codes of the file-accessing function calls it expects to receive.If an NFS client has problems in communicating to a NFS server (e.g. if the server’s responses are dropped on the network), we’ll see a different behaviour between the mount options “hard” and “soft”. Full Story

Running “ls -la /” hangs, yet running “ls -la” to other root directories  (i.e. ls -la /usr) does NOT hang. And the system logs ( i.e. /var/adm/messages) shows NFS related errors, even though this is NOT a true NFS client.

Here are the some sample errors that may appear in the /var/adm/messages file when the “ls -la /” hangs:

Mar 28 09:23:19 moe nfs: [ID 333984 kern.notice] NFS server for volume management (/vol) not responding still trying
Mar 28 09:31:13 moe nfs: [ID 664466 kern.notice] NFS getattr failed for server for volume management (/vol): error 23 (RPC: Unitdata error)

In this particular situation, this client was mounting a CD remotely from another system, which was shutdown before unsharing the CD, and before the client could unmount the remote CD mount. The tail end of a truss shows that it was hanging on /vol as well (line numbers set and it was hanging on line 256-257):

# cd /
# truss -fall -vall -wall -rall ls -la

Full Story

When we trying to use a particular RPC  program, below may indicate that rpcbind is not running or the program is not registered with rpcbind.

Error “RPC: Program not registered”

Full Story

NFS (Network File System) for Beginners: In this post I am trying to build a base for the beginners. This post will help to proceed further with NFS complex tasks.

What is NFS?

NFS —> Network File System —> The Network File System (NFS) is a client-server service that enables users to view, store, and update files on a remote server as though they were on the their own local server. In Simple layman language NFS provides a “Centralized File Access”.

Example: Suppose you have a 100 users in a company. Out of which 50 require complete access to 10 files/softwares etc. for there daily day to day work and other 50 require access to other commonly used 15 files/softwares etc. for there work. Now instead of placing individual files/softwares on each users server (computer) you should keep the files/softwares in a common shared place which users would have access to. Now each user can access (read/write/modify –> depending upon access provided) those commonly used files/softwares remotely without having them on his/her local server/computer. This will help to save the diskspace as well on all users server. Full Story