statd(8) — Linux manual page


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

NAME         top

       rpc.statd - NSM service daemon

SYNOPSIS         top

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

DESCRIPTION         top

       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 system reboots

              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 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 manager.


       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

       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 monitor list
       on persistent storage after each reboot.

OPTIONS         top

       -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 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
              This string is only used by the sm-notify command as the
              source address from which to send reboot notification

              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.  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 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 directory.  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.


       Many of the options that can be set on the command line can also
       be controlled through values set in the [statd] or, in some
       cases, the [lockd] sections of the /etc/nfs.conf configuration
       file.  Values recognized in the [statd] section include port,
       outgoing-port, name, state-directory-path, and ha-callout which
       each have the same effect as the option with the same name.

       The values recognized in the [lockd] section include port and
       udp-port which have the same effect as the --nlm-port and --nlm-
       udp-port options, respectively.

SECURITY         top

       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 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


       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, 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 second is the mon_name of the monitored peer.  The
       third is the caller_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

   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 'visible' in /etc/netconfig.  As
       long as at least one network transport listener starts
       successfully, rpc.statd will operate.

ENVIRONMENT         top

              If set to a positive integer, has the same effect as

FILES         top

              directory containing monitor list

              directory containing notify list

              NSM state number for this host

              pid file

              network transport capability database

SEE ALSO         top

       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

AUTHORS         top

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

COLOPHON         top

       This page is part of the nfs-utils (NFS utilities) project.
       Information about the project can be found at 
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       bug report for this manual page, see
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       obtained from the project's upstream Git repository
       ⟨git://⟩ on
       2023-12-22.  (At that time, the date of the most recent commit
       that was found in the repository was 2023-12-05.)  If you
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                             1 November 2009                RPC.STATD(8)

Pages that refer to this page: nfs(5)nfs.conf(5)nfsconf(8)nfsdclnts(8)sm-notify(8)