man > rpc.sm-notify(8)

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

NAME
       sm-notify - send reboot notifications to NFS peers

SYNOPSIS
       /usr/sbin/sm-notify [-dfn] [-m minutes] [-v name] [-p notify-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 re‐
       booted.  After an NFS client reboots, an NFS server must release all file locks held  by  ap‐
       plications  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:

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

       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

       The local NFS lock manager alerts its local rpc.statd of each remote peer that should be mon‐
       itored.  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.

NSM OPERATION IN DETAIL
       The first file locking interaction between an NFS client and server causes the NFS lock  man‐
       agers  on  both peers to contact their local NSM service to store information about the oppo‐
       site peer.  On Linux, the local lock manager contacts rpc.statd.

       rpc.statd records information about each monitored NFS peer on persistent storage.  This  in‐
       formation  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  man‐
       ager 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 no‐
       tify 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 moni‐
       tored 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  re‐
       quest,  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-no‐
       tify 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
       -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 unre‐
              sponsive hosts.  If this option is not specified, sm-notify attempts to send notifica‐
              tions 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  re‐
              mote's mon_name from being resolved to an address.

              Hosts  are  not  removed  from  the notification list until a valid reply has been re‐
              ceived.  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  notifica‐
              tions.  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 spec‐
              ified, 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  no‐
              tification from a specific network address.

CONFIGURATION FILE
       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 configura‐
       tion file.

       Values recognized in the [sm-notify] section include: retry-time, outgoing-port,  and  outgo‐
       ing-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-no‐
       tify will lift lockd's grace period early if it has no hosts to notify.  Some high availabil‐
       ity 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 corre‐
       sponding command line option.

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


SECURITY
       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  direc‐
       tory.   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.

ADDITIONAL NOTES
       Lock  recovery after a reboot is critical to maintaining data integrity and preventing unnec‐
       essary 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 con‐
              tact 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  re‐
       moves 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 sys‐
       tems that do not support TI-RPC or IPv6.

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

FILES
       /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

       /proc/sys/fs/nfs/nsm_local_state
                                kernel's copy of the NSM state number

SEE ALSO
       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
       Olaf Kirch <okir AT suse.de>
       Chuck Lever <chuck.lever AT oracle.com>

                                           1 November 2009                              SM-NOTIFY(8)