Ubuntu Manpage: rpc.statd - NSM service daemon

Provided by: nfs-common_1.3.4-2.5ubuntu3.7_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]
                 [--nlm-port port] [--nlm-udp-port port]

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.

-T, --nlm-port port
Specifies the port number that lockd should listen on for NLM requests. This sets both the TCP
and UDP ports unless the UDP port is set separately.

-U, --nlm-udp-port port
Specifies the UDP port number that lockd should listen on for NLM requests.

-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, or when it receives SM_NOTIFY. 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 del-client or sm-notify 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 for add-client or del-client , otherwise it is IP_address of the caller sending SM_NOTIFY. The
forth is the state_value in the SM_NOTIFY request.

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)