rpc.mountd - NFS mount daemon


   /usr/sbin/rpc.mountd [options]


   The  rpc.mountd  daemon  implements  the  server  side of the NFS MOUNT
   protocol, an NFS side protocol used by NFS version 2 [RFC1094] and  NFS
   version 3 [RFC1813].

   An NFS server maintains a table of local physical file systems that are
   accessible to NFS clients.  Each file system in this table is  referred
   to as an exported file system, or export, for short.

   Each  file  system  in  the  export  table  has an access control list.
   rpc.mountd uses these access control lists to determine whether an  NFS
   client  is permitted to access a given file system.  For details on how
   to manage your NFS  server's  export  table,  see  the  exports(5)  and
   exportfs(8) man pages.

   Mounting exported NFS File Systems
   The  NFS  MOUNT protocol has several procedures.  The most important of
   these are MNT (mount an export) and UMNT (unmount an export).

   A MNT request has two arguments: an explicit argument that contains the
   pathname  of  the  root  directory  of the export to be mounted, and an
   implicit argument that is the sender's IP address.

   When receiving a MNT request from an NFS client, rpc.mountd checks both
   the  pathname and the sender's IP address against its export table.  If
   the sender is permitted to  access  the  requested  export,  rpc.mountd
   returns  an  NFS  file  handle  for  the export's root directory to the
   client.  The client can then use the root file handle  and  NFS  LOOKUP
   requests to navigate the directory structure of the export.

   The rmtab File
   The  rpc.mountd daemon registers every successful MNT request by adding
   an entry to the /var/lib/nfs/rmtab file.  When receivng a UMNT  request
   from  an  NFS client, rpc.mountd simply removes the matching entry from
   /var/lib/nfs/rmtab, as long as the access control list for that  export
   allows that sender to access the export.

   Clients  can  discover  the  list  of  file  systems  an  NFS server is
   currently exporting, or the list of other clients that have mounted its
   exports,  by  using  the showmount(8) command.  showmount(8) uses other
   procedures in the NFS MOUNT protocol to report  information  about  the
   server's exported file systems.

   Note,  however,  that there is little to guarantee that the contents of
   /var/lib/nfs/rmtab are accurate.  A client may  continue  accessing  an
   export even after invoking UMNT.  If the client reboots without sending
   a  UMNT  request,   stale   entries   remain   for   that   client   in


   -d kind  or  --debug kind
          Turn on debugging. Valid kinds are: all, auth, call, general and

   -F  or  --foreground
          Run in foreground (do not daemonize)

   -f  or  --exports-file
          This option specifies the exports file, listing the clients that
          this server is prepared to serve and parameters to apply to each
          such mount (see exports(5)).  By default, export information  is
          read from /etc/exports.

   -h  or  --help
          Display usage message.

   -o num  or  --descriptors num
          Set the limit of the number of open file descriptors to num. The
          default is to leave the limit unchanged.

   -N  or  --no-nfs-version
          This option can be used to request that rpc.mountd do not  offer
          certain  versions  of NFS. The current version of rpc.mountd can
          support both NFS version 2, 3 and 4. If the either one of  these
          version  should  not be offered, rpc.mountd must be invoked with
          the option --no-nfs-version <vers> .

   -n  or  --no-tcp
          Don't advertise TCP for mount.

   -P     Ignored (compatibility with unfsd??).

   -p  or  --port num
          Specifies the port number used for  RPC  listener  sockets.   If
          this  option  is  not  specified, rpc.mountd will try to consult
          /etc/services, if gets port succeed, set the same port  for  all
          listener  socket,  otherwise chooses a random ephemeral port for
          each listener socket.

          This option can be used to fix the port  value  of  rpc.mountd's
          listeners  when  NFS  MOUNT  requests  must  traverse a firewall
          between clients and servers.

   -H  or  --ha-callout prog
          Specify a  high  availability  callout  program.   This  program
          receives  callouts  for  all  MOUNT  and UNMOUNT requests.  This
          allows rpc.mountd to be used in a High Availability NFS (HA-NFS)

          The callout program is run with 4 arguments.  The first is mount
          or unmount depending on the reason for the callout.  The  second
          will  be the name of the client performing the mount.  The third
          will be the path that the client is mounting.  The last  is  the
          number  of  concurrent  mounts that we believe the client has of
          that path.

          This callout is not needed with 2.6 and later kernels.  Instead,
          mount the nfsd filesystem on /proc/fs/nfsd.

   -s, --state-directory-path directory
          Specify  a  directory in which to place statd state information.
          If this option is not specified the default of  /var/lib/nfs  is

   -r, --reverse-lookup
          rpc.mountd  tracks  IP addresses in the rmtab file.  When a DUMP
          request is made (by someone running showmount -a, for instance),
          it  returns  IP  addresses instead of hostnames by default. This
          option causes rpc.mountd to perform a reverse lookup on each  IP
          address  and  return  that  hostname instead.  Enabling this can
          have a  substantial  negative  effect  on  performance  in  some

   -t N or --num-threads=N
          This   option  specifies  the  number  of  worker  threads  that
          rpc.mountd spawns.  The default is 1 thread, which  is  probably
          enough.   More  threads  are usually only needed for NFS servers
          which need to handle mount storms of hundreds of NFS mounts in a
          few seconds, or when your DNS server is slow or unreliable.

   -V  or  --nfs-version
          This option can be used to request that rpc.mountd offer certain
          versions of NFS. The current version of rpc.mountd  can  support
          both NFS version 2 and the newer version 3.

   -v  or  --version
          Print the version of rpc.mountd and exit.

   -g  or  --manage-gids
          Accept  requests  from  the  kernel  to map user id numbers into
          lists of group id numbers for use in  access  control.   An  NFS
          request  will  normally  (except  when  using  Kerberos or other
          cryptographic authentication) contains a user-id and a  list  of
          group-ids.   Due to a limitation in the NFS protocol, at most 16
          groups ids can be listed.  If you use the -g flag, then the list
          of group ids received from the client will be replaced by a list
          of group ids determined by an appropriate lookup on the  server.
          Note  that  the 'primary' group id is not affected so a newgroup
          command on the client will still be  effective.   This  function
          requires a Linux Kernel with version at least 2.6.21.


   You can protect your rpc.mountd listeners using the tcp_wrapper library
   or iptables(8).

   Note that the tcp_wrapper library supports only IPv4 networking.

   Add the hostnames of NFS peers that are allowed to access rpc.mountd to
   /etc/hosts.allow.   Use  the  daemon name mountd even if the rpc.mountd
   binary has a different name.

   Hostnames used in either access file will be ignored when they can  not
   be resolved into IP addresses.  For further information see the tcpd(8)
   and hosts_access(5) man pages.

   IPv6 and TI-RPC support
   TI-RPC is a pre-requisite  for  supporting  NFS  on  IPv6.   If  TI-RPC
   support  is  built  into  rpc.mountd, it attempts to start listeners on
   network transports marked 'visible' in /etc/netconfig.  As long  as  at
   least  one  network  transport listener starts successfully, rpc.mountd
   will operate.


   /etc/exports             input  file  for  exportfs,  listing  exports,
                            export options, and access control lists

   /var/lib/nfs/rmtab       table of clients accessing server's exports


   exportfs(8),  exports(5),  showmount(8),  rpc.nfsd(8),  rpc.rquotad(8),
   nfs(5), tcpd(8), hosts_access(5), iptables(8), netconfig(5)

   RFC 1094 - "NFS: Network File System Protocol Specification"
   RFC 1813 - "NFS Version 3 Protocol Specification"


   Olaf Kirch, H. J. Lu, G. Allan Morris III, and a host of others.

                              31 Dec 2009                    rpc.mountd(8)


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.