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 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 '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
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 <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>