SM-NOTIFY(8)                                                                                                        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 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 sys-
       tem 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 moni-
       tored.  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 mon-
       itor 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  regis-
              tered, 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  speci-
              fied, sm-notify uses /var/lib/nfs/statd 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 send-
              ing 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  con-
       tinue  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/statd/sm    directory containing monitor list

       /var/lib/nfs/statd/sm.bak
                                directory containing notify list

       /var/lib/nfs/statd/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 <okirATsuse.de>
       Chuck Lever <chuck.leverAToracle.com>



                                                         1 November 2009                                            SM-NOTIFY(8)