nfs-utils-1.2.2/utils/statd/statd.man

.\"@(#)rpc.statd.8"
.\"
.\" Copyright (C) 1999 Olaf Kirch <okir@monad.swb.de>
.\" Modified by Jeffrey A. Uphoff, 1999, 2002, 2005.
.\" Modified by Lon Hohberger, 2000.
.\" Modified by Paul Clements, 2004.
.\"
.\" Rewritten by Chuck Lever <chuck.lever@oracle.com>, 2009.
.\" Copyright 2009 Oracle.  All rights reserved.
.\"
.TH RPC.STATD 8 "1 November 2009
.SH NAME
rpc.statd \- NSM service daemon
.SH SYNOPSIS
.BI "rpc.statd [-dh?FLNvVw] [-H " prog "] [-n " my-name "] [-o " outgoing-port "] [-p " listener-port "] [-P " path " ]
.SH DESCRIPTION
File locks are not part of persistent file system state.
Lock state is thus lost when a host reboots.
.PP
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.
.PP
For NFS version 2 [RFC1094] and NFS version 3 [RFC1813], the
.I 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:
.TP
.B 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
.TP
.B sm-notify
A helper program that notifies NFS peers after the local system reboots
.PP
The local NFS lock manager alerts its local
.B rpc.statd
of each remote peer that should be monitored.
When the local system reboots, the
.B sm-notify
command notifies the NSM service on monitored peers of the reboot.
When a remote reboots, that peer notifies the local
.BR rpc.statd ,
which in turn passes the reboot notification
back to the local NFS lock manager.
.SH 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
.BR rpc.statd .
.PP
.B 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.
.PP
An NFS client sends a hostname, known as the client's
.IR 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.
.PP
The Linux NFS server can provide the client's
.I caller_name
or the client's network address to
.BR rpc.statd .
For the purposes of the NSM protocol,
this name or address is known as the monitored peer's
.IR mon_name .
In addition, the local lock manager tells
.B rpc.statd
what it thinks its own hostname is.
For the purposes of the NSM protocol,
this hostname is known as
.IR my_name .
.PP
There is no equivalent interaction between an NFS server and a client
to inform the client of the server's
.IR caller_name .
Therefore NFS clients do not actually know what
.I 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.
.SS Reboot notification
When the local system reboots, the
.B 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
.I mon_name
string as the destination.
To identify which host has rebooted, the
.B sm-notify
command normally sends the results of
.BR gethostname (3)
as the
.I my_name
string.
The remote
.B 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.
.PP
If
.B 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
.IR "NSM state number" ,
a 32-bit integer that is bumped after each reboot by the
.B sm-notify
command.
.B rpc.statd
uses this number to distinguish between actual reboots
and replayed notifications.
.PP
Part of NFS lock recovery is rediscovering
which peers need to be monitored again.
The
.B sm-notify
command clears the monitor list on persistent storage after each reboot.
.SH OPTIONS
.TP
.BR -d , " --no-syslog
Causes
.B rpc.statd
to write log messages on
.I stderr
instead of to the system log,
if the
.B -F
option was also specified.
.TP
.BR -F , " --foreground
Keeps
.B 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,
.B rpc.statd
backgrounds itself soon after it starts.
.TP
.BR -h , " -?" , " --help
Causes
.B rpc.statd
to display usage information on
.I stderr
and then exit.
.TP
.BI "\-H," "" " \-\-ha-callout " prog
Specifies a high availability callout program.
If this option is not specified, no callouts are performed.
See the
.B High-availability callouts
section below for details.
.TP
.BR -L , " --no-notify
Prevents
.B rpc.statd
from running the
.B sm-notify
command when it starts up,
preserving the existing NSM state number and monitor list.
.IP
Note: the
.B sm-notify
command contains a check to ensure it runs only once after each system reboot.
This prevents spurious reboot notification if
.B rpc.statd
restarts without the
.B -L
option.
.TP
.BI "\-n, " "" "\-\-name " ipaddr " | " hostname
Specifies the bind address used for RPC listener sockets.
The
.I ipaddr
form can be expressed as either an IPv4 or an IPv6 presentation address.
If this option is not specified,
.B rpc.statd
uses a wildcard address as the transport bind address.
.IP
This string is also passed to the
.B sm-notify
command to be used as the source address from which
to send reboot notification requests.
See
.BR sm-notify (8)
for details.
.TP
.BR -N
Causes
.B rpc.statd
to run the
.B sm-notify
command, and then exit.
Since the
.B sm-notify
command can also be run directly, this option is deprecated.
.TP
.BI "\-o," "" " \-\-outgoing\-port "  port
Specifies the source port number the
.B sm-notify
command should use when sending reboot notifications.
See
.BR sm-notify (8)
for details.
.TP
.BI "\-p," "" " \-\-port " port
Specifies the port number used for RPC listener sockets.
If this option is not specified,
.B rpc.statd
chooses a random ephemeral port for each listener socket.
.IP
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.
.TP
.BI "\-P, " "" \-\-state\-directory\-path " pathname
Specifies the pathname of the parent directory
where NSM state information resides.
If this option is not specified,
.B rpc.statd
uses
.I /var/lib/nfs
by default.
.IP
After starting,
.B rpc.statd
attempts to set its effective UID and GID to the owner
and group of this directory.
.TP
.BR -v ", " -V ", " --version
Causes
.B rpc.statd
to display version information on
.I stderr
and then exit.
.SH SECURITY
The
.B 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
.B 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.
.PP
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
.B rpc.statd
chooses, simply use
.BR chown (1)
to set the owner of
the state directory.
.PP
You can also protect your
.B rpc.statd
listeners using the
.B tcp_wrapper
library or
.BR iptables (8).
To use the
.B tcp_wrapper
library, add the hostnames of peers that should be allowed access to
.IR /etc/hosts.allow .
Use the daemon name
.B statd
even if the
.B rpc.statd
binary has a different filename.
.P
For further information see the
.BR tcpd (8)
and
.BR hosts_access (5)
man pages.
.SH ADDITIONAL NOTES
Lock recovery after a reboot is critical to maintaining data integrity
and preventing unnecessary application hangs.
.PP
To help
.B rpc.statd
match SM_NOTIFY requests to NLM requests, a number of best practices
should be observed, including:
.IP
The UTS nodename of your systems should match the DNS names that NFS
peers use to contact them
.IP
The UTS nodenames of your systems should always be fully qualified domain names
.IP
The forward and reverse DNS mapping of the UTS nodenames should be
consistent
.IP
The hostname the client uses to mount the server should match the server's
.I mon_name
in SM_NOTIFY requests it sends
.IP
The use of network addresses as a
.I mon_name
or a
.I my_name
string should be avoided when
interoperating with non-Linux NFS implementations.
.PP
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.
.PP
On Linux, if the
.B 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.
.SS High-availability callouts
.B 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.
.PP
The name of the callout program is specified with the
.B -H
option.
The program is run with 3 arguments:
The first is either
.B add-client
or
.B del-client
depending on the reason for the callout.
The second is the
.I mon_name
of the monitored peer.
The third is the
.I caller_name
of the requesting lock manager.
.SS IPv6 and TI-RPC support
TI-RPC is a pre-requisite for supporting NFS on IPv6.
If TI-RPC support is built into
.BR rpc.statd ,
it attempts to start listeners on network transports marked
'visible' in
.IR /etc/netconfig .
As long as at least one network transport listener starts successfully,
.B rpc.statd
will operate.
.SH FILES
.TP 2.5i
.I /var/lib/nfs/sm
directory containing monitor list
.TP 2.5i
.I /var/lib/nfs/sm.bak
directory containing notify list
.TP 2.5i
.I /var/lib/nfs/state
NSM state number for this host
.TP 2.5i
.I /var/run/run.statd.pid
pid file
.TP 2.5i
.I /etc/netconfig
network transport capability database
.SH SEE ALSO
.BR sm-notify (8),
.BR nfs (5),
.BR rpc.nfsd (8),
.BR rpcbind (8),
.BR tcpd (8),
.BR hosts_access (5),
.BR iptables (8),
.BR netconfig (5)
.sp
RFC 1094 - "NFS: Network File System Protocol Specification"
.br
RFC 1813 - "NFS Version 3 Protocol Specification"
.br
OpenGroup Protocols for Interworking: XNFS, Version 3W - Chapter 11
.SH AUTHORS
Jeff Uphoff <juphoff@users.sourceforge.net>
.br
Olaf Kirch <okir@monad.swb.de>
.br
H.J. Lu <hjl@gnu.org>
.br
Lon Hohberger <hohberger@missioncriticallinux.com>
.br
Paul Clements <paul.clements@steeleye.com>
.br
Chuck Lever <chuck.lever@oracle.com>