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NAME | SYNOPSIS | DESCRIPTION | NSM OPERATION IN DETAIL | OPTIONS | CONFIGURATION FILE | SECURITY | ADDITIONAL NOTES | FILES | SEE ALSO | AUTHORS | COLOPHON |
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SM-NOTIFY(8) System Manager's Manual SM-NOTIFY(8)
sm-notify - send reboot notifications to NFS peers
/usr/sbin/sm-notify [-dfn] [-m minutes] [-v name] [-p notify-port]
[-P path]
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.
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.
-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
requests.
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 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.
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.
/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
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
Olaf Kirch <okir@suse.de>
Chuck Lever <chuck.lever@oracle.com>
This page is part of the nfs-utils (NFS utilities) project.
Information about the project can be found at
⟨http://linux-nfs.org/wiki/index.php/Main_Page⟩. If you have a bug
report for this manual page, see
⟨http://linux-nfs.org/wiki/index.php/Main_Page⟩. This page was
obtained from the project's upstream Git repository
⟨git://git.linux-nfs.org/projects/steved/nfs-utils.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-27.) 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 man-pages@man7.org
1 November 2009 SM-NOTIFY(8)
Pages that refer to this page: nfs(5), nfs.conf(5), statd(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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