Manpages - statd.8

rpc.statd - NSM service daemon

rpc.statd [-dh?FLNvV] [-H */prog/*] [-n */my-name/*] [-o */outgoing-port/*]

[-p */listener-port/*] [-P */path/*]

[–nlm-port */port/*] [–nlm-udp-port */port/*]

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.

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.

-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/

This string is only used by the sm-notify command as the source address from which to send reboot notification requests.

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. 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.

Many of the options that can be set on the command line can also be controlled through values set in the [statd] or, in some cases, the [lockd] sections of the /etc/nfs.conf configuration file. Values recognized in the [statd] section include port, outgoing-port, name, state-directory-path, and ha-callout which each have the same effect as the option with the same name.

The values recognized in the [lockd] section include port and udp-port which have the same effect as the –nlm-port and –nlm-udp-port options, respectively.

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.

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.

RPC_STATD_NO_NOTIFY=

If set to a positive integer, has the same effect as –no-notify.

/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

*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

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>