nfsd(7)		       Miscellaneous Information Manual		       nfsd(7)



NAME
       nfsd - special filesystem for controlling Linux NFS server

SYNPOSIS
       mount -t nfsd nfsd /proc/fs/nfsd

DESCRIPTION
       The  nfsd  filesystem  is a special filesystem which provides access to
       the Linux NFS server.  The filesystem consists of  a  single  directory
       which  contains	a  number of files.  These files are actually gateways
       into the NFS server.  Writing to them can affect the  server.   Reading
       from them can provide information about the server.

       This  file  system is only available in Linux 2.6 and later series ker-
       nels (and in the later parts of the 2.5 development series  leading  up
       to 2.6).	 This man page does not apply to 2.4 and earlier.

       As  well	 as  this  filesystem,	there are a collection of files in the
       procfs filesystem (normally mounted at /proc) which are used to control
       the NFS server.	This manual page describes all of these files.

       The exportfs and mountd programs (part of the nfs-utils package) expect
       to find this filesystem mounted at /proc/fs/nfsd or  /proc/fs/nfs.   If
       it  is  not  mounted,  they  will fall-back on 2.4 style functionality.
       This involves accessing the NFS server via a systemcall.	 This  system-
       call is scheduled to be removed after the 2.6 kernel series.

DETAILS
       The three files in the nfsd filesystem are:

       exports
	      This  file  contains  a  list  of filesystems that are currently
	      exported and  clients  that  each	 filesystem  is	 exported  to,
	      together	with a list of export options for that client/filesys-
	      tem pair.	 This is similar to the /proc/fs/nfs/exports  file  in
	      2.4.  One difference is that a client doesn't necessarily corre-
	      spond to just one host.  It can respond to a large collection of
	      hosts that are being treated identically.

	      Each line of the file contains a path name, a client name, and a
	      number of options in parentheses.	 Any space,  tab,  newline  or
	      back-slash  character  in	 the  path name or client name will be
	      replaced by a backslash followed by the  octal  ASCII  code  for
	      that character.


       threads
	      This  file  represents  the number of nfsd thread currently run-
	      ning.  Reading it will show the number of threads.   Writing  an
	      ASCII  decimal  number  will  cause  the number of threads to be
	      changed (increased or decreased as necessary)  to	 achieve  that
	      number.


       filehandle
	      This  is	a  somewhat unusual file  in that what is read from it
	      depends on what was just written to it.  It provides a  transac-
	      tional  interface	 where	a  program  can open the file, write a
	      request, and read a response.  If two  separate  programs	 open,
	      write,  and  read	 at  the same time, their requests will not be
	      mixed up.

	      The request written to filehandle should be  a  client  name,  a
	      path  name, and a number of bytes.  This should be followed by a
	      newline, with white-space separating the fields, and octal quot-
	      ing of special characters.

	      On  writing  this, the program will be able to read back a file-
	      handle for that path as exported to the given client.  The file-
	      handle's length will be at most the number of bytes given.

	      The filehandle will be represented in hex with a leading '\x'.

       The  directory /proc/net/rpc in the procfs filesystem contains a number
       of files and directories.  The files contain  statistics	 that  can  be
       display using the nfsstat program.  The directories contain information
       about various caches that the NFS server maintains  to  keep  track  of
       access  permissions  that different clients have for different filesys-
       tems.  The caches are:


       auth.domain
	      This cache maps the name of a client (or domain) to an  internal
	      data  structure.	 The  only access that is possible is to flush
	      the cache.


       auth.unix.ip
	      This cache contains a mapping from IP address to the name of the
	      authentication  domain  that  the ipaddress should be treated as
	      part of.


       nfsd.export
	      This cache contains a  mapping  from  directory  and  domain  to
	      export options.


       nfsd.fh
	      This cache contains a mapping from domain and a filesystem iden-
	      tifier to a directory.   The filesystem identifier is stored  in
	      the  filehandles and consists of a number indicating the type of
	      identifier and a number of hex bytes indicating the  content  of
	      the identifier.


       Each  directory	representing a cache can hold from 1 to 3 files.  They
       are:

       flush  When a number of seconds since epoch (1 Jan 1970) is written  to
	      this  file,  all	entries	 in  the  cache that were last updated
	      before that file become invalidated and  will  be	 flushed  out.
	      Writing  1  will	flush  everything.  This is the only file that
	      will always be present.


       content
	      This file, if present, contains a textual representation of ever
	      entry  in	 the cache, one per line.  If an entry is still in the
	      cache (because it is actively being used) but has expired or  is
	      otherwise	 invalid,  it  will  be presented as a comment (with a
	      leading hash character).


       channel
	      This file, if present, acts a channel for request from the  ker-
	      nel-based	 nfs  server  to be passed to a user-space program for
	      handling.

	      When the kernel needs some information which isn't in the cache,
	      it  makes	 a  line appear in the channel file giving the key for
	      the information.	A user-space program should  read  this,  find
	      the answer, and write a line containing the key, an expiry time,
	      and the content.	For example the kernel might make
		   nfsd 127.0.0.1
	      appear in the auth.unix.ip/content file.	The user-space program
	      might then write
		   nfsd 127.0.0.1 1057206953 localhost
	      to indicate that 127.0.0.1 should map to localhost, at least for
	      now.

	      If the program uses select(2) or poll(2) to discover if  it  can
	      read from the channel then it will never see and end-of-file but
	      when all requests	 have  been  answered,	it  will  block	 until
	      another request appears.


       In  the	/proc filesystem there are 4 files that can be used to enabled
       extra tracing of nfsd and related code.	They are:
	    /proc/sys/sunrpc/nfs_debug
	    /proc/sys/sunrpc/nfsd_debug
	    /proc/sys/sunrpc/nlm_debug
	    /proc/sys/sunrpc/rpc_debug
       They control tracing for the NFS client, the NFS	 server,  the  Network
       Lock  Manager (lockd) and the underlying RPC layer respectively.	 Deci-
       mal numbers can be read from or written to these	 files.	  Each	number
       represents  a bit-pattern where bits that are set cause certain classes
       of tracing to be enabled.  Consult the kernel header files to find  out
       what number correspond to what tracing.


SEE ALSO
       rpc.nfsd(8), exports(5), nfsstat(8), mountd(8) exportfs(8).


AUTHOR
       NeilBrown



				  3 July 2003			       nfsd(7)