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    Command:

    rpc.mountd

    
    
    

    SYNOPSIS

           /usr/sbin/rpc.mountd [options]
    
    
    

    DESCRIPTION

           The  rpc.mountd daemon implements the server side of the NFS MOUNT pro-
           tocol, 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 cur-
           rently 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
           /var/lib/nfs/rmtab.
    
           -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 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
                  used.
    
           -r, --reverse-lookup
    
           -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 cryp-
                  tographic 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.
    
    
    

    TCP_WRAPPERS SUPPORT

           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  sup-
           port  is  built into rpc.mountd, it attempts to start listeners on net-
           work transports marked 'visible' in  /etc/netconfig.   As  long  as  at
           least  one  network  transport listener starts successfully, rpc.mountd
           will operate.
    
    
    

    FILES

           /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
    
    
    

    SEE ALSO

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