Ubuntu Manpage: rpc.statd - NSM service daemon

Provided by: nfs-common_1.2.8-9ubuntu12.3_amd64

NAME

       rpc.statd - NSM service daemon

SYNOPSIS

       rpc.statd  [-dh?FLNvV]  [-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 will try to consult /etc/services, if gets port succeed, set
the same port for all listener socket, otherwise 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 by default.

After starting, rpc.statd 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, rpc.statd only needs to access files in sm and sm.bak within the state-
directory-path.

-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 'visible' in
/etc/netconfig. As long as at least one network transport listener starts successfully,
rpc.statd will operate.

FILES

       /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

       /run/run.statd.pid       pid file

       /etc/netconfig           network transport capability database

AUTHORS

       Jeff Uphoff <juphoff@users.sourceforge.net>
       Olaf Kirch <okir@monad.swb.de>
       H.J. Lu <hjl@gnu.org>
       Lon Hohberger <hohberger@missioncriticallinux.com>
       Paul Clements <paul.clements@steeleye.com>
       Chuck Lever <chuck.lever@oracle.com>

                                         1 November 2009                             RPC.STATD(8)