rpc.mountd(8)						      System Manager's Manual						     rpc.mountd(8)

NAME

       rpc.mountd - NFS mount daemon

SYNOPSIS

       /usr/sbin/rpc.mountd [options]

DESCRIPTION

       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
       /var/lib/nfs/rmtab.

OPTIONS

       -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 sup-
	      port 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/ser-
	      vices, 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  num-
	      ber 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
	      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.

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 support 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)

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

AUTHOR

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

								    31 Dec 2009 						     rpc.mountd(8)