сервисный демон NSM (NSM service daemon)
Имя (Name)
rpc.statd - NSM service daemon
Синопсис (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]
Описание (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.
Детали операции NSM (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.
Параметры (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
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.
Конфигурационный файл (Config file)
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.
Безопасность (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.
Дополнительные замечания (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.
Окружение (Environment)
RPC_STATD_NO_NOTIFY=
If set to a positive integer, has the same effect as
--no-notify.
Файлы (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
Смотри также (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
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