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nfsd(7)                                                                nfsd(7)



NAME
       nfsd - special filesystem for controlling Linux NFS server

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

DESCRIPTION
       The  nfsd filesytem is a special filesystem which provides access to the Linux NFS server.  The filesystem con-
       sists 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 systemcall 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  back-
              slash 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 newline, 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 filehandles 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 ipad-
              dress 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 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 kernel-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, atleast 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.  Decimal 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)