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 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 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

       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

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

       -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-

       -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 requests.

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


       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 file.

       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-path.

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 IPv6.

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

FILES         top

       /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

                                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 11

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 
       ⟨⟩.  If you have a bug
       report for this manual page, see
       ⟨⟩.  This page was
       obtained from the project's upstream Git repository
       ⟨;a=summary⟩ on
       2020-07-14.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-06-18.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

                               1 November 2009                  SM-NOTIFY(8)

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