NFS
Section: Protocols (4P)
Updated: 9 July 1986
Index
Return to Main Contents
NAME
nfs, NFS - network file system
SYNOPSIS
options NFS
DESCRIPTION
The Network File System, or NFS,
allows a client workstation to perform
transparent file access over the network.
Using it, a client
workstation can operate on files
that reside on a variety of servers,
server architectures
and across a variety of operating systems.
Client file access calls
are converted to NFS protocol requests,
and are 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.
The Nework File System operates in a stateless fashion
using remote procedure (RPC) calls
built on top of external data representation (XDR) protocol.
The RPC protocol provides for version and authentication parameters
to be exchanged
to ensure security over the network.
A server can grant access to a specific filesystem to certain clients
by adding an entry for that filesystem to the server's
/etc/exports
file.
A client gains access to that filesystem with the
mount(2)
system call,
which requests a file handle for the filesystem itself.
Once the filesystem is mounted by the client,
the server issues a file handle to the client
for each file (or directory) the client accesses.
If the file is somehow removed on the server side,
the file handle becomes stale (dissociated with a known file).
A server may also be a client
with respect to filesystems it has mounted over the network,
but its clients cannot gain access to those filesystems.
Instead,
the client must mount a filesystem 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 inhibits super-user privileges on remote filesystems.
ERRORS
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 will see the console message:
-
NFS: file server not responding: still trying.
The client continues (forever) to resend the request
until it receives an acknowledgement from the server.
This means the server can crash or power down, and come back up,
without any special action required by the client.
It also means the client process requesting the I/O will block
and remain insensitive to signals,
sleeping inside the kernel at
PRIBIO.
SEE ALSO
exports(5), fstab(5), mntent(5), mount(2), mount(8), nfsd(8)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- ERRORS
-
- SEE ALSO
-
This document was created by
man2html,
using the manual pages.
Time: 17:20:24 GMT, March 25, 2025