RPC.STATD(8)                                                                                                        RPC.STATD(8)



NAME
       rpc.statd - NSM service daemon

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

DESCRIPTION
       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:

       rpc.statd
              A daemon that listens for reboot notifications from other hosts, and manages the list of hosts to be notified when
              the local system reboots

       sm-notify
              A helper program that notifies NFS peers after the local system reboots

       The  local NFS lock manager alerts its local rpc.statd of each remote peer that should be monitored.  When the local sys-
       tem 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 manager.

NSM OPERATION IN DETAIL
       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 persistent 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 rebooted.

       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  number,  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 monitored again.  The sm-notify command clears the mon-
       itor list on persistent storage after each reboot.

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

       -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 exit.

       -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 list.

              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 presentation 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 details.

       -p, --port port
              Specifies  the  port  number  used for RPC listener sockets.  If this option is not specified, rpc.statd 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 speci-
              fied, rpc.statd uses /var/lib/nfs/statd by default.

              After starting, rpc.statd attempts to set its effective UID and GID to the owner and group of this directory.

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

SECURITY
       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  con-
       tinue  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 hostnames 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 filename.

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

ADDITIONAL NOTES
       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 qualified 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 monitoring 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 operation, 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 successful 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 support is built into rpc.statd, it  attempts  to  start
       listeners  on  network  transports marked /etc/netconfig.  As long as at least one network transport listener starts suc-
       cessfully, rpc.statd will operate.

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

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

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

       /var/run/run.statd.pid   pid file

       /etc/netconfig           network transport capability database

SEE ALSO
       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

AUTHORS
       Jeff Uphoff <juphoffATusers.net>
       Olaf Kirch <okirATmonad.de>
       H.J. Lu <hjlATgnu.org>
       Lon Hohberger <hohbergerATmissioncriticallinux.com>
       Paul Clements <paul.clementsATsteeleye.com>
       Chuck Lever <chuck.leverAToracle.com>



                                                         1 November 2009                                            RPC.STATD(8)