nfsd(7) — Linux manual page


nfsd(7)             Miscellaneous Information Manual             nfsd(7)

NAME         top

       nfsd - special filesystem for controlling Linux NFS server

SYNPOSIS         top

       mount -t nfsd nfsd /proc/fs/nfsd

DESCRIPTION         top

       The nfsd filesystem is a special filesystem which provides access
       to the Linux NFS server.  Writing to files in this filesystem can
       affect the server.  Reading from them can provide information
       about the server.

       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

DETAILS         top

       Files in the nfsd filesystem include:

              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.

              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.

              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 filehandle's length will be at most the number of
              bytes given.

              The filehandle will be represented in hex with a leading

              This directory contains a subdirectory for each NFSv4
              client.  Each file under that subdirectory gives some
              details about the client in YAML format.  In addition,
              writing "expire\n" to the ctl file will force the server
              to immediately revoke all state held by that client.

       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:

              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
              export options.

              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 a time in the future (in seconds
              since epoch) 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
              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
              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 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:
       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.

NOTES         top

       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

       Previously the nfsctl systemcall was used for communication
       between nfsd and user utilities.  That systemcall was removed in
       kernel version 3.1.  Older nfs-utils versions were able to fall
       back to nfsctl if necessary; that was removed from nfs-utils

SEE ALSO         top

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

AUTHOR         top


COLOPHON         top

       This page is part of the nfs-utils (NFS utilities) project.
       Information about the project can be found at 
       ⟨⟩.  If you have a
       bug report for this manual page, see
       ⟨⟩.  This page was
       obtained from the project's upstream Git repository
       ⟨git://⟩ on
       2023-12-22.  (At that time, the date of the most recent commit
       that was found in the repository was 2023-12-05.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to

                               3 July 2003                       nfsd(7)

Pages that refer to this page: nfsservctl(2)nfsd(8)