Provided by: nfs-common_1.2.5-3ubuntu3_amd64 bug

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
       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:

       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
       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.

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 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

       -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 this directory.

       -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 address.

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
       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.

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.

   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

       /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@suse.de>
       Chuck Lever <chuck.lever@oracle.com>

                                         1 November 2009                             SM-NOTIFY(8)