Requires Optional NFS Services Software

NAME

nfs, NFS − network file system

DESCRIPTION

The Network File System (NFS) allows a client node to perform transparent file access over the network.  By using NFS, a client node operates on files residing on a variety of servers and server architectures, and across a variety of operating systems.  File access calls on the client (such as read requests) are converted to NFS protocol requests and sent to the server system over the network.  The server receives the request, performs the actual file system operation, and sends a response back to the client. 

NFS operates in a stateless manner using remote procedure calls (RPC) built on top of an external data representation (XDR) protocol.  The RPC protocol enables version and authentication parameters to be exchanged for security over the network. 

A server grants access to a specific file system to clients by adding an entry for that file system to the server’s /etc/exports file. 

A client gains access to that file system using the mount(1M) command to request a file handle for the file system. (A file handle is the means by which NFS identifies remote files.)  Once a client mounts the file system, the server issues a file handle to the client for each file (or directory) the client accesses.  If the file is removed on the server side, the file handle becomes stale (dissociated with a known file), and the server returns the errno ESTALE. 

A server can also be a client with respect to file systems it has mounted over the network; however, its clients cannot directly access those file systems.  If a client attempts to mount a file system for which the server is an NFS client, the server returns the errno EREMOTE.  The client must mount the file system directly from the server on which it resides. 

The user ID and group ID mappings must be the same between client and server.  However, the server maps UID 0 (the super-user) to UID −2 before performing access checks for a client.  This process inhibits super-user privileges on remote file systems. 

RETURN VALUE

Generally, physical disk I/O errors detected at the server are returned to the client for action.  If the server is down or inaccessible, the client receives the message:

NFS:  file server not responding: still trying. 

The client continues resending the request until it receives an acknowledgement from the server.  Therefore, the server can crash or power down, and come back up without any special action required by the client.  The client process requesting the I/O will block, but remains sensitive to signals (unless mounted with the "nointr" option) until the server recovers.  However, if mounted with the "soft" option, the client process returns an error instead of waiting indefinitely. 

AUTHOR

nfs was developed by Sun Microsystems, Inc. 

SEE ALSO

mount(1M), nfsd(1M), vfsmount(2), checklist(4), exports(4). 

Hewlett-Packard Company  —  HP-UX Release 8.05: June 1991