sm-notify(8) — Linux manual page


SM-NOTIFY(8)             System Manager's Manual            SM-NOTIFY(8)

NAME         top

       sm-notify - send reboot notifications to NFS peers

SYNOPSIS         top

       /usr/sbin/sm-notify [-dfn] [-m minutes] [-v name] [-p notify-
       port] [-P path]

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 and version 3, 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 helper program that notifies NFS peers after the local
              system reboots

              A daemon that listens for reboot notifications from other
              hosts, and manages the list of hosts to be notified when
              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
       records the server's hostname used on 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 normally sends
       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     Keeps sm-notify attached to its controlling terminal and
              running in the foreground so that notification progress
              may be monitored directly.

       -f     Send notifications even if sm-notify has already run since
              the last system reboot.

       -m retry-time
              Specifies the length of time, in minutes, to continue
              retrying notifications to unresponsive hosts.  If this
              option is not specified, sm-notify attempts to send
              notifications for 15 minutes.  Specifying a value of 0
              causes sm-notify to continue sending notifications to
              unresponsive peers until it is manually killed.

              Notifications are retried if sending fails, the remote
              does not respond, the remote's NSM service is not
              registered, or if there is a DNS failure which prevents
              the remote's mon_name from being resolved to an address.

              Hosts are not removed from the notification list until a
              valid reply has been received.  However, the SM_NOTIFY
              procedure has a void result.  There is no way for sm-
              notify to tell if the remote recognized the sender and has
              started appropriate lock recovery.

       -n     Prevents sm-notify from updating the local system's NSM
              state number.

       -p port
              Specifies the source port number sm-notify should use when
              sending reboot notifications.  If this option is not
              specified, a randomly chosen ephemeral port is used.

              This option can be used to traverse a firewall between
              client and server.

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

              After starting, sm-notify 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, sm-
              notify only needs to access files in sm and sm.bak within
              the state-directory-path.

       -v ipaddr | hostname
              Specifies the network address from which to send reboot
              notifications, and the mon_name argument to use when
              sending SM_NOTIFY requests.  If this option is not
              specified, sm-notify uses a wildcard address as the
              transport bind address, and uses the my_name recorded when
              the remote was monitored as the mon_name argument when
              sending SM_NOTIFY requests.

              The ipaddr form can be expressed as either an IPv4 or an
              IPv6 presentation address.  If the ipaddr form is used,
              the sm-notify command converts this address to a hostname
              for use as the mon_name argument when sending SM_NOTIFY

              This option can be useful in multi-homed configurations
              where the remote requires notification from a specific
              network address.


       Many of the options that can be set on the command line can also
       be controlled through values set in the [sm-notify] or, in one
       case, the [statd] section of the /etc/nfs.conf configuration

       Values recognized in the [sm-notify] section include: retry-time,
       outgoing-port, and outgoing-addr.  These have the same effect as
       the command line options m, p, and v respectively.

       An additional value recognized in the [sm-notify] section is
       lift-grace.  By default, sm-notify will lift lockd's grace period
       early if it has no hosts to notify.  Some high availability
       configurations will run one sm-notify per floating IP address.
       In these configurations, lifting the grace period early may
       prevent clients from reclaiming locks.  Setting lift-grace to n
       will prevent sm-notify from ending the grace period early.  lift-
       grace has no corresponding command line option.

       The value recognized in the [statd] section is state-directory-

SECURITY         top

       The sm-notify command must be started as root to acquire
       privileges needed to access the state information database.  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.


       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.

   IPv6 and TI-RPC support
       TI-RPC is a pre-requisite for supporting NFS on IPv6.  If TI-RPC
       support is built into the sm-notify command ,it will choose an
       appropriate IPv4 or IPv6 transport based on the network address
       returned by DNS for each remote peer.  It should be fully
       compatible with remote systems that do not support TI-RPC or

       Currently, the sm-notify command supports sending notification
       only via datagram transport protocols.

FILES         top

              directory containing monitor list

              directory containing notify list

              NSM state number for this host

              kernel's copy of the NSM state number

SEE ALSO         top

       rpc.statd(8), nfs(5), uname(2), hostname(7)

       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

       Olaf Kirch <>
       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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                             1 November 2009                SM-NOTIFY(8)

Pages that refer to this page: nfs(5)nfs.conf(5)statd(8)