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NAME | SYNOPSIS | DESCRIPTION | NSM OPERATION IN DETAIL | OPTIONS | CONFIGURATION FILE | SECURITY | ADDITIONAL NOTES | FILES | SEE ALSO | AUTHORS | COLOPHON |
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 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.
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
⟨http://git.linux-nfs.org/?p=steved/nfs-utils.git;a=summary⟩ on
2017-07-05. If you discover any rendering problems in this HTML ver‐
sion 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 man‐
ual 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)