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 kernels (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  sys-
       temcall 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/filesystem pair.  This is similar to the /proc/fs/nfs/exports file in 2.4.  One	difference
	      is  that	a  client  doesn't  necessarily correspond 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 running.  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  transactional
	      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  new-
	      line, with white-space separating the fields, and octal quoting of special characters.

	      On writing this, the program will be able to read back a filehandle for that path as exported to the given client.  The filehandle'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 filesystems.  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 identifier 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 iden-
	      tifier.

       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 kernel-based nfs server to be passed to a  user-space	program  for  han-
	      dling.

	      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

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

AUTHOR

       NeilBrown

								    3 July 2003 							   nfsd(7)