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RPC.STATD


Section: Maintenance Commands (8)
Updated: 1 November 2009
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NAME

rpc.statd – NSM service daemon
 

SYNOPSIS

rpc.statd [-dh?FLNvVw] [-H prog] [-n my-name] [-o outgoing-port] [-p listener-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 [RFC1094] and NFS version 3 [RFC1813], 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:


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
sm-notify


A helper program that notifies NFS peers after 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 uses the server hostname from 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 sends the
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, –no-syslog


Causes
rpc.statd

to write log messages on
stderr

instead of to the system log,
if the
-F

option was also specified.

-F, –foreground


Keeps
rpc.statd

attached to its controlling terminal so that NSM
operation can be monitored directly or run under a debugger.
If this option is not specified,
rpc.statd

backgrounds itself soon after it starts.

-h, -?, –help


Causes
rpc.statd

to display usage information on
stderr

and then exit.

-H, –ha-callout prog


Specifies a high availability callout program.
If this option is not specified, no callouts are performed.
See the
High-availability callouts

section below for details.

-L, –no-notify


Prevents
rpc.statd

from running the
sm-notify

command when it starts up,
preserving the existing NSM state number and monitor list.


Note: the
sm-notify

command contains a check to ensure it runs only once after each system reboot.
This prevents spurious reboot notification if
rpc.statd

restarts without the
-L

option.

-n, –name ipaddr | hostname


Specifies the bind address used for RPC listener sockets.
The
ipaddr

form can be expressed as either an IPv4 or an IPv6 presentation address.
If this option is not specified,
rpc.statd

uses a wildcard address as the transport bind address.


This string is also passed to the
sm-notify

command to be used as the source address from which
to send reboot notification requests.
See
sm-notify(8)

for details.

-N


Causes
rpc.statd

to run the
sm-notify

command, and then exit.
Since the
sm-notify

command can also be run directly, this option is deprecated.

-o, –outgoing-port port


Specifies the source port number the
sm-notify

command should use when sending reboot notifications.
See
sm-notify(8)

for details.

-p, –port port


Specifies the port number used for RPC listener sockets.
If this option is not specified,
rpc.statd

chooses a random ephemeral port for each listener socket.


This option can be used to fix the port value of its listeners when
SM_NOTIFY requests must traverse a firewall between clients and servers.
-P, –state-directory-path pathname


Specifies the pathname of the parent directory
where NSM state information resides.
If this option is not specified,
rpc.statd

uses
/var/lib/nfs/statd

by default.


After starting,
rpc.statd

attempts to set its effective UID and GID to the owner
and group of this directory.

-v, -V, –version


Causes
rpc.statd

to display version information on
stderr

and then exit.


 

SECURITY

The
rpc.statd

daemon must be started as root to acquire privileges needed
to create sockets with privileged source ports, and to access the
state information database.
Because
rpc.statd

maintains a long-running network service, however, 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.

You can also protect your
rpc.statd

listeners using the
tcp_wrapper

library or
iptables(8).

To use the
tcp_wrapper

library, add the hostnames of peers that should be allowed access to
/etc/hosts.allow.

Use the daemon name
statd

even if the
rpc.statd

binary has a different filename.

For further information see the
tcpd(8)

and
hosts_access(5)

man pages.
 

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.
 

High-availability callouts

rpc.statd

can exec a special callout program during processing of
successful SM_MON, SM_UNMON, and SM_UNMON_ALL requests.
Such a program may be used in High Availability NFS (HA-NFS)
environments to track lock state that may need to be migrated after
a system reboot.

The name of the callout program is specified with the
-H

option.
The program is run with 3 arguments:
The first is either
add-client

or
del-client

depending on the reason for the callout.
The second is the
mon_name

of the monitored peer.
The third is the
caller_name

of the requesting lock manager.
 

IPv6 and TI-RPC support

TI-RPC is a pre-requisite for supporting NFS on IPv6.
If TI-RPC support is built into
rpc.statd,

it attempts to start listeners on network transports marked

/etc/netconfig.

As long as at least one network transport listener starts successfully,
rpc.statd

will operate.
 

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
/var/run/run.statd.pid


pid file
/etc/netconfig


network transport capability database

 

SEE ALSO

sm-notify(8),

nfs(5),

rpc.nfsd(8),

rpcbind(8),

tcpd(8),

hosts_access(5),

iptables(8),

netconfig(5)


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

Jeff Uphoff <[email protected]>

Olaf Kirch <[email protected]>

H.J. Lu <[email protected]>

Lon Hohberger <[email protected]>

Paul Clements <[email protected]>

Chuck Lever <[email protected]>



 

Index



NAME

SYNOPSIS

DESCRIPTION

NSM OPERATION IN DETAIL


Reboot notification


OPTIONS

SECURITY

ADDITIONAL NOTES


High-availability callouts

IPv6 and TI-RPC support


FILES

SEE ALSO

AUTHORS



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