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NFS(4P)								       NFS(4P)

       nfs, NFS	- network file system

       options NFS

       The Network File	System,	or NFS,	allows a client	workstation to perform
       transparent file	access over the	network.  Using	it, a client  worksta-
       tion  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 Network File	System operates	in a stateless	fashion	 using	remote
       procedure  (RPC)	 calls	built  on  top of external data	representation
       (XDR) protocol.	These protocols	are documented	in  The	 RPC  protocol
       provides	 for version and authentication	parameters to be exchanged for
       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 and	running	exportfs(8).

       A client	gains access to	that  filesystem  with	the  mount(2V)	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 or creates.
       If the file is somehow removed on the server side, the file handle  be-
       comes 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 be-
       fore performing access checks for a client.  This  inhibits  super-user
       privileges  on  remote  filesystems.  This may be changed by use	of the
       "anon" export option.  See exportfs(8).

       NFS-related routines and	structure definitions are described in

       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 server host not responding still trying.
       Depending on whether the	file system has	been mounted "hard" or	"soft"
       (see  mount(8)),	 the  client will either  continue (forever) to	resend
       the request until it receives an	acknowledgement	from  the  server,  or
       return  an error	to user-level.	For hard mounts, this means the	server
       can crash or power down and come	back up	without	any special action re-
       quired  by the client.  If the "intr" mount option was not specified, a
       client process requesting I/O will block	and remain insensitive to sig-
       nals,  sleeping inside the kernel at PRIBIO until the request is	satis-


       mount(2V),  exports(5),	fstab(5),  fstab(5),  exportfs(8),   mount(8),
       nfsd(8),	sticky(8)

       When  a	file that is opened by a client	is unlinked (by	the server), a
       file with a name	of the form .nfsXXX (where XXX is a number) is created
       by  the	client.	 When the open file is closed, the .nfsXXX file	is re-
       moved.  If the client crashes before the	file can be closed,  the  .nf-
       sXXX file is not	removed.

       NFS  servers  usually mark their	clients' swap files specially to avoid
       being required to sync their  inodes  to	 disk  before  returning  from
       writes.	See sticky(8).

			       24 November 1987			       NFS(4P)


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