Provided by: nfs-kernel-server_1.2.8-6ubuntu1.2_amd64 bug


       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 parse.

       -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) environment.

              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

              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 used.

       -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 situations.

       -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)