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]
                 [--nlm-port port] [--nlm-udp-port port]

       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.

       -T, --nlm-port port
              Specifies the port number that lockd should listen  on  for  NLM
              requests.   This  sets both the TCP and UDP ports unless the UDP
              port is set separately.

       -U, --nlm-udp-port port
              Specifies the UDP port number that lockd should  listen  on  for
              NLM requests.

       -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,  or  when  it
       receives SM_NOTIFY.  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 del-
       client or sm-notify depending on the reason for the callout.  The  sec-
       ond  is  the  mon_name  of  the monitored peer.  The third is the call-
       er_name of the requesting lock manager for add-client or  del-client  ,
       otherwise  it is IP_address of the caller sending SM_NOTIFY.  The forth
       is the state_value in the SM_NOTIFY request.

   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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