Reference Manual

Version 6.2

Table of Contents




Module Summary

Erlang interface towards epmd


This module communicates with the EPMD daemon, see epmd. To implement your own epmd module please see ERTS User's Guide: How to Implement an Alternative Service Discovery for Erlang Distribution


start_link() -> {ok, pid()} | ignore | {error, term()}

This function is invoked as this module is added as a child of the erl_distribution supervisor.

register_node(Name, Port) -> Result
register_node(Name, Port, Driver) -> Result


Name = string()
Port = integer() >= 0
Driver = inet_tcp | inet6_tcp | inet | inet6
Creation = integer() >= 0
Result = {ok, Creation} | {error, already_registered} | term()

Registers the node with epmd and tells epmd what port will be used for the current node. It returns a creation number. This number is incremented on each register to help with identifying if a node is reconnecting to epmd.

port_please(Name, Host) -> {ok, Port, Version} | noport
port_please(Name, Host, Timeout) -> {ok, Port, Version} | noport


Name = string()
Timeout = integer() >= 0 | infinity
Port = Version = integer() >= 0

Requests the distribution port for the given node of an EPMD instance. Together with the port it returns a distribution protocol version which has been 5 since Erlang/OTP R6.

address_please(Name, Host, AddressFamily) ->
                  Success | {error, term()}


Name = string()
Host = string() | inet:ip_address()
AddressFamily = inet | inet6
Port = Version = integer() >= 0
Success =
    {ok, inet:ip_address()} |
    {ok, inet:ip_address(), Port, Version}

Called by the distribution module. Resolves the Host to an IP address.

Another epmd module may return port and distribution protocol version as well.

names(Host) -> {ok, [{Name, Port}]} | {error, Reason}


Host = atom() | string() | inet:ip_address()
Name = string()
Port = integer() >= 0
Reason = address | file:posix()

Called by net_adm:names/0. Host defaults to the localhost. Returns the names and associated port numbers of the Erlang nodes that epmd registered at the specified host. Returns {error, address} if epmd is not operational.


(arne@dunn)1> erl_epmd:names(localhost).