nfsd(7)                Miscellaneous Information Manual                nfsd(7)

       nfsd - special filesystem for controlling Linux NFS server

       mount -t nfsd nfsd /proc/fs/nfsd

       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.

       The three files in the nfsd filesystem are:

              This  file contains a list of filesystems that are currently ex-
              ported 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 re-
              placed by a backslash followed by the octal ASCII code for  that

              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

              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 re-
              quest, 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 ac-
       cess permissions that different clients have for different filesystems.
       The caches are:

              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.

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

              This cache contains a mapping from directory and domain  to  ex-
              port options.

              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

       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 be-
              fore that file become  invalidated  and  will  be  flushed  out.
              Writing  1  will  flush  everything.  This is the only file that
              will always be present.

              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).

              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

              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
              appear in the auth.unix.ip/content file.  The user-space program
              might then write
                   nfsd 1057206953 localhost
              to indicate that should map to localhost, at least for

              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  an-
              other 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:
       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.

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


                                  3 July 2003                          nfsd(7)
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