bionic (8) rpc.mountd.8.gz

Provided by: nfs-kernel-server_1.3.4-2.1ubuntu5.5_amd64 bug

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)

       -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 mountd-version  or  --no-nfs-version mountd-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 num  or  -P num  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  prog 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
              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 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.

       -u  or  --no-udp
              Don't advertise UDP for mounting

       -V version  or  --nfs-version 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 network 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)