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epmd(1)				 User Commands			       epmd(1)

NAME
       epmd  -	Erlang Port Mapper Daemonepmd [-d|-debug] [DbgExtra...]	[-port
       No] [-daemon] [-relaxed_command_check]Starts the	port mapper daemonepmd
       [-d|-debug]  [-port  No]	 [-names|-kill|-stop  Name]Communicates	with a
       running port mapper daemon

DESCRIPTION
       This daemon acts	as a name server on all	hosts involved in  distributed
       Erlang  computations.  When  an Erlang node starts, the node has	a name
       and it obtains an address from the host OS kernel. The name and the ad-
       dress  are  sent	 to  the  epmd	daemon running on the local host. In a
       TCP/IP environment, the address consists	of the IP address and  a  port
       number.	The  name of the node is an atom on the	form of	Name@Node. The
       job of the epmd daemon is to keep track of which	node name  listens  on
       which  address.	Hence,	epmd  maps  symbolic node names	to machine ad-
       dresses.

       The TCP/IP epmd daemon actually only keeps track	of  the	 Name  (first)
       part of an Erlang node name. The	Host part (whatever is after the @) is
       implicit	in the node name where the epmd	daemon was actually contacted,
       as  is  the IP address where the	Erlang node can	be reached. Consistent
       and correct TCP naming services are therefore required  for  an	Erlang
       network to function correctly.

	 Starting the port mapper daemon:
	   The	daemon is started automatically	by the erl command if the node
	   is to be distributed	and there is no	running	instance  present.  If
	   automatically  launched,  environment  variables have to be used to
	   alter the behavior of the daemon.  See  the	Environment  variables
	   section below.

	   If the -daemon argument is not given, epmd runs as a	normal program
	   with	the controlling	terminal of the	shell in which it is  started.
	   Normally, it	should run as a	daemon.

	   Regular  start-up options are described in the Regular options sec-
	   tion	below.

	   The DbgExtra	options	are described in the DbgExtra options  section
	   below.

	 Communicating with a running port mapper daemon:
	   Communicating  with	the  running  epmd daemon by means of the epmd
	   program is done primarily for debugging purposes.

	   The different queries are described in the Interactive options sec-
	   tion	below.

REGULAR	OPTIONS
       These  options  are available when starting the actual name server. The
       name server is normally started automatically by	the  erl  command  (if
       not  already  available),  but  it  can	also be	started	at i.e.	system
       start-up.

	 -address List:
	   Let this instance of	epmd listen only on the	 comma-separated  list
	   of  IP  addresses  and on the loopback address (which is implicitly
	   added to the	list if	it has not been	specified). This can  also  be
	   set	using  the ERL_EPMD_ADDRESS environment	variable. See the sec-
	   tion	Environment variables below.

	 -port No:
	   Let this instance of	epmd listen to another TCP port	 than  default
	   4369.  This	can  also  be  set using the ERL_EPMD_PORT environment
	   variable. See the section Environment variables below

	 -d | -debug:
	   Enable debug	output.	The more -d flags given, the more debug	output
	   you	will get (to a certain limit). This option is most useful when
	   the epmd daemon is not started as a daemon.

	 -daemon:
	   Start epmd detached from the	controlling terminal. Logging will end
	   up  in  syslog when available and correctly configured. If the epmd
	   daemon is started at	boot, this option should definitely  be	 used.
	   It is also used when	the erl	command	automatically starts epmd.

	 -relaxed_command_check:
	   Start  the  epmd  program with relaxed command checking (mostly for
	   backward compatibility). This affects the following:

	   * With relaxed command checking, the	epmd daemon can	be killed from
	     the localhost with	i.e. epmd -kill	even if	there are active nodes
	     registered. Normally only daemons with an empty node database can
	     be	killed with the	epmd -kill command.

	   * The  epmd	-stop command (and the corresponding messages to epmd,
	     as	can be given using erl_interface/ei) is	 normally  always  ig-
	     nored,  as	 it  opens  up	the possibility	of a strange situation
	     where two nodes of	the same name can be alive at the same time. A
	     node  unregisters	itself by just closing the connection to epmd,
	     which is why the stop command was only intended for use in	debug-
	     ging situations.

	     With  relaxed command checking enabled, you can forcibly unregis-
	     ter live nodes.

	   Relaxed command checking can	also be	enabled	by setting  the	 envi-
	   ronment  variable  ERL_EPMD_RELAXED_COMMAND_CHECK prior to starting
	   epmd.

	   Only	use relaxed command checking on	systems	with very limited  in-
	   teractive usage.

DBGEXTRA OPTIONS
       These  options  are purely for debugging	and testing epmd clients. They
       should not be used in normal operation.

	 -packet_timeout Seconds:
	   Set the number of seconds a connection can be inactive before  epmd
	   times out and closes	the connection (default	60).

	 -delay_accept Seconds:
	   To  simulate	a busy server you can insert a delay between when epmd
	   gets	notified that a	new connection is requested and	when the  con-
	   nection gets	accepted.

	 -delay_write Seconds:
	   Also	 a simulation of a busy	server.	Inserts	a delay	before a reply
	   is sent.

INTERACTIVE OPTIONS
       These options make epmd run as an interactive command,  displaying  the
       results	of sending queries to an already running instance of epmd. The
       epmd contacted is always	on the local node, but the -port option	can be
       used to select between instances	if several are running using different
       ports on	the host.

	 -port No:
	   Contacts the	epmd listening on the given TCP	port  number  (default
	   4369).  This	 can  also  be set using the ERL_EPMD_PORT environment
	   variable. See the section Environment variables below.

	 -names:
	   List	names registered with the currently running epmd

	 -kill:
	   Kill	the currently running epmd.

	   Killing the running epmd is only allowed if epmd  -names  shows  an
	   empty database or -relaxed_command_check was	given when the running
	   instance of epmd was	started. Note that  -relaxed_command_check  is
	   given  when	starting  the daemon that is to	accept killing when it
	   has live nodes registered. When running  epmd  interactively,  -re-
	   laxed_command_check has no effect. A	daemon that is started without
	   relaxed command checking has	to be killed  using  i.e.  signals  or
	   some	other OS specific method if it has active clients registered.

	 -stop Name:
	   Forcibly unregister a live node from	epmd's database

	   This	 command  can  only  be	 used  when  contacting	epmd instances
	   started with	the -relaxed_command_check  flag.  Note	 that  relaxed
	   command  checking  has to be	enabled	for the	epmd daemon contacted.
	   When	running	epmd interactively, -relaxed_command_check has no  ef-
	   fect.

ENVIRONMENT VARIABLES
	 ERL_EPMD_ADDRESS:
	   This	 environment  variable may be set to a comma-separated list of
	   IP addresses, in which case the epmd	daemon will listen only	on the
	   specified address(es) and on	the loopback address (which is implic-
	   itly	added to the list if it	has not	been specified).  The  default
	   behaviour is	to listen on all available IP addresses.

	 ERL_EPMD_PORT:
	   This	 environment  variable	can  contain the port number epmd will
	   use.	The default port will work fine	in  most  cases.  A  different
	   port	 can  be  specified to allow several instances of epmd,	repre-
	   senting independent clusters	of nodes,  to  co-exist	 on  the  same
	   host. All nodes in a	cluster	must use the same epmd port number.

	 ERL_EPMD_RELAXED_COMMAND_CHECK:
	   If  set  prior to start, the	epmd daemon will behave	as if the -re-
	   laxed_command_check option was given	at start-up. Consequently,  if
	   this	 option	is set before starting the Erlang virtual machine, the
	   automatically started epmd will accept the -kill and	-stop commands
	   without restrictions.

LOGGING
       On  some	operating systems syslog will be used for error	reporting when
       epmd runs as an daemon. To enable the error logging you	have  to  edit
       /etc/syslog.conf	file and add an	entry

	     !epmd
	     *.*<TABs>/var/log/epmd.log

       where  <TABs> are at least one real tab character. Spaces will silently
       be ignored.

ACCESS RESTRICTIONS
       The epmd	daemon accepts messages	from both localhost and	remote	hosts.
       However,	 only  the query commands are answered (and acted upon)	if the
       query comes from	a remote host. It is always an error to	try to	regis-
       ter  a nodename if the client is	not a process located on the same host
       as the epmd instance is running on- such	requests are  considered  hos-
       tile and	the connection is immediately closed.

       The queries accepted from remote	nodes are:

	 * Port	 queries  - i.e. on which port does the	node with a given name
	   listen

	 * Name	listing	- i.e. give a list of all names	registered on the host

       To restrict access further, firewall software has to be used.

Ericsson AB			   erts	6.4			       epmd(1)

NAME | DESCRIPTION | REGULAR OPTIONS | DBGEXTRA OPTIONS | INTERACTIVE OPTIONS | ENVIRONMENT VARIABLES | LOGGING | ACCESS RESTRICTIONS

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