RPC.STATD(8)                System Manager's Manual               RPC.STATD(8)

       rpc.statd - NSM service daemon

       rpc.statd  [-dh?FLNvV]  [-H  prog]  [-n my-name] [-o outgoing-port] [-p
       listener-port] [-P path ]

       File locks are not part of persistent file system state.  Lock state is
       thus lost when a host reboots.

       Network file systems must also detect when lock state is lost because a
       remote host has rebooted.  After an NFS client reboots, an  NFS  server
       must  release  all file locks held by applications that were running on
       that client.  After a server reboots, a client must remind  the  server
       of file locks held by applications running on that client.

       For  NFS  version  2 [RFC1094] and NFS version 3 [RFC1813], the Network
       Status Monitor protocol (or NSM for short) is used to notify NFS  peers
       of  reboots.   On  Linux, two separate user-space components constitute
       the NSM service:

              A daemon that listens for reboot notifications from other hosts,
              and manages the list of hosts to be notified when the local sys-
              tem reboots

              A helper program that notifies NFS peers after the local  system

       The  local  NFS  lock manager alerts its local rpc.statd of each remote
       peer that should be monitored.  When the local system reboots, the  sm-
       notify  command  notifies  the  NSM  service  on monitored peers of the
       reboot.  When a remote reboots, that peer notifies the local rpc.statd,
       which in turn passes the reboot notification back to the local NFS lock

       The first file locking interaction between an  NFS  client  and  server
       causes  the  NFS lock managers on both peers to contact their local NSM
       service to store information about the opposite peer.   On  Linux,  the
       local lock manager contacts rpc.statd.

       rpc.statd  records information about each monitored NFS peer on persis-
       tent storage.  This information describes how to contact a remote  peer
       in case the local system reboots, how to recognize which monitored peer
       is reporting a reboot, and how to notify the local lock manager when  a
       monitored peer indicates it has rebooted.

       An  NFS  client sends a hostname, known as the client's caller_name, in
       each file lock request.  An NFS server can use this  hostname  to  send
       asynchronous  GRANT  calls  to a client, or to notify the client it has

       The Linux NFS server  can  provide  the  client's  caller_name  or  the
       client's  network  address  to  rpc.statd.  For the purposes of the NSM
       protocol, this name  or  address  is  known  as  the  monitored  peer's
       mon_name.   In addition, the local lock manager tells rpc.statd what it
       thinks its own hostname is.  For the purposes of the NSM protocol, this
       hostname is known as my_name.

       There  is  no equivalent interaction between an NFS server and a client
       to inform the  client  of  the  server's  caller_name.   Therefore  NFS
       clients  do  not actually know what mon_name an NFS server might use in
       an SM_NOTIFY request.  The Linux NFS client uses  the  server  hostname
       from the mount command to identify rebooting NFS servers.

   Reboot notification
       When  the local system reboots, the sm-notify command reads the list of
       monitored peers from persistent storage and sends an SM_NOTIFY  request
       to  the  NSM  service on each listed remote peer.  It uses the mon_name
       string as the destination.  To identify which host  has  rebooted,  the
       sm-notify  command  sends  the my_name string recorded when that remote
       was  monitored.   The  remote  rpc.statd  matches  incoming   SM_NOTIFY
       requests  using this string, or the caller's network address, to one or
       more peers on its own monitor list.

       If rpc.statd does not find a peer on its monitor list that  matches  an
       incoming  SM_NOTIFY  request,  the notification is not forwarded to the
       local lock manager.  In addition, each peer has its own NSM state  num-
       ber, a 32-bit integer that is bumped after each reboot by the sm-notify
       command.  rpc.statd uses this  number  to  distinguish  between  actual
       reboots and replayed notifications.

       Part of NFS lock recovery is rediscovering which peers need to be moni-
       tored again.  The sm-notify command clears the monitor list on  persis-
       tent storage after each reboot.

       -d, --no-syslog
              Causes  rpc.statd  to write log messages on stderr instead of to
              the system log, if the -F option was also specified.

       -F, --foreground
              Keeps rpc.statd attached to its controlling terminal so that NSM
              operation can be monitored directly or run under a debugger.  If
              this option is not specified, rpc.statd backgrounds itself  soon
              after it starts.

       -h, -?, --help
              Causes rpc.statd to display usage information on stderr and then

       -H, --ha-callout prog
              Specifies a high availability callout program.  If  this  option
              is  not  specified,  no  callouts  are performed.  See the High-
              availability callouts section below for details.

       -L, --no-notify
              Prevents rpc.statd from running the sm-notify  command  when  it
              starts  up, preserving the existing NSM state number and monitor

              Note: the sm-notify command contains a check to ensure  it  runs
              only  once  after  each  system  reboot.  This prevents spurious
              reboot notification if rpc.statd restarts without the -L option.

       -n, --name ipaddr | hostname
              Specifies the bind address used for RPC listener  sockets.   The
              ipaddr  form  can be expressed as either an IPv4 or an IPv6 pre-
              sentation address.  If this option is not  specified,  rpc.statd
              uses a wildcard address as the transport bind address.

              This  string  is also passed to the sm-notify command to be used
              as the source address from which  to  send  reboot  notification
              requests.  See sm-notify(8) for details.

       -N     Causes  rpc.statd  to  run the sm-notify command, and then exit.
              Since the sm-notify command  can  also  be  run  directly,  this
              option is deprecated.

       -o, --outgoing-port port
              Specifies  the  source  port number the sm-notify command should
              use when sending reboot  notifications.   See  sm-notify(8)  for

       -p, --port port
              Specifies  the  port  number  used for RPC listener sockets.  If
              this option is not specified,  rpc.statd  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 its listeners
              when SM_NOTIFY requests must traverse a firewall between clients
              and servers.

       -P, --state-directory-path pathname
              Specifies  the  pathname of the parent directory where NSM state
              information resides.  If this option is not specified, rpc.statd
              uses /var/lib/nfs by default.

              After  starting, rpc.statd attempts to set its effective UID and
              GID to the owner and group of the subdirectory sm of this direc-
              tory.  After changing the effective ids, rpc.statd only needs to
              access files in sm and sm.bak within the state-directory-path.

       -v, -V, --version
              Causes rpc.statd to display version information  on  stderr  and
              then exit.

       The  rpc.statd  daemon  must  be  started as root to acquire privileges
       needed to create sockets with privileged source ports,  and  to  access
       the  state  information  database.  Because rpc.statd maintains a long-
       running network service, however, it drops root privileges as  soon  as
       it starts up to reduce the risk of a privilege escalation attack.

       During  normal operation, the effective user ID it chooses is the owner
       of the state directory.  This allows it to continue to access files  in
       that  directory  after  it has dropped its root privileges.  To control
       which user ID rpc.statd chooses, simply use chown(1) to set  the  owner
       of the state directory.

       You  can  also  protect  your rpc.statd listeners using the tcp_wrapper
       library or iptables(8).  To use the tcp_wrapper library, add the  host-
       names  of peers that should be allowed access to /etc/hosts.allow.  Use
       the daemon name statd even if the  rpc.statd  binary  has  a  different

       For further information see the tcpd(8) and hosts_access(5) man pages.

       Lock  recovery after a reboot is critical to maintaining data integrity
       and preventing unnecessary application hangs.  To help rpc.statd  match
       SM_NOTIFY  requests  to NLM requests, a number of best practices should
       be observed, including:

              The UTS nodename of your systems should match the DNS names that
              NFS peers use to contact them

              The  UTS nodenames of your systems should always be fully quali-
              fied domain names

              The forward and reverse DNS mapping of the UTS nodenames  should
              be consistent

              The  hostname  the  client uses to mount the server should match
              the server's mon_name in SM_NOTIFY requests it sends

       Unmounting an NFS file system does not necessarily stop either the  NFS
       client  or  server from monitoring each other.  Both may continue moni-
       toring each other for a time in case subsequent NFS traffic between the
       two results in fresh mounts and additional file locking.

       On  Linux,  if the lockd kernel module is unloaded during normal opera-
       tion, all remote NFS peers are unmonitored.  This can happen on an  NFS
       client, for example, if an automounter removes all NFS mount points due
       to inactivity.

   High-availability callouts
       rpc.statd can exec a special callout program during processing of  suc-
       cessful  SM_MON,  SM_UNMON,  and SM_UNMON_ALL requests.  Such a program
       may be used in High Availability NFS  (HA-NFS)  environments  to  track
       lock state that may need to be migrated after a system reboot.

       The  name  of the callout program is specified with the -H option.  The
       program is run with 3 arguments: The first is either add-client or del-
       client  depending  on  the  reason  for the callout.  The second is the
       mon_name of the monitored peer.  The third is the  caller_name  of  the
       requesting lock manager.

   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.statd, 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.statd will operate.

       /var/lib/nfs/sm          directory containing monitor list

       /var/lib/nfs/sm.bak      directory containing notify list

       /var/lib/nfs/state       NSM state number for this host

       /run/       pid file

       /etc/netconfig           network transport capability database

       sm-notify(8),     nfs(5),     rpc.nfsd(8),     rpcbind(8),     tcpd(8),
       hosts_access(5), iptables(8), netconfig(5)

       RFC 1094 - "NFS: Network File System Protocol Specification"
       RFC 1813 - "NFS Version 3 Protocol Specification"
       OpenGroup Protocols for Interworking: XNFS, Version 3W - Chapter 11

       Jeff Uphoff <>
       Olaf Kirch <>
       H.J. Lu <>
       Lon Hohberger <>
       Paul Clements <>
       Chuck Lever <>

                                1 November 2009                   RPC.STATD(8)
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