# erl_epmd

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Module

erl_epmd

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Module Summary

Erlang interface towards epmd

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Since

Module erl_epmd was introduced in OTP R14B.

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Description

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 Node Discovery for Erlang Distribution

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Exports

####
start_link() -> {ok, pid()} | ignore | {error, term()}
OTP 21.0

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

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register_node(Name, Port) -> Result
OTP 21.0

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register_node(Name, Port, Driver) -> Result
OTP 21.0

### Types

Name = string()
Port = integer() >= 0
Driver = inet_tcp | inet6_tcp | inet | inet6
Creation = integer() >= 0 | -1
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 differentiate a new node instance connecting to epmd with the same name.

After the node has successfully registered with epmd it will automatically attempt reconnect to the daemon if the connection is broken.

####
port_please(Name, Host) ->
{port, Port, Version} |
noport | closed |
{error, term()}
OTP 21.0

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port_please(Name, Host, Timeout) ->
{port, Port, Version} |
noport | closed |
{error, term()}
OTP 21.0

### Types

Name = atom() | string()
Host = atom() | string() | inet:ip_address()
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.

####
listen_port_please(Name, Host) -> {ok, Port}
OTP 23.0

### Types

Name = atom() | string()
Host = atom() | string() | inet:ip_address()
Port = integer() >= 0

Called by the distribution module to get which port the local node should listen to when accepting new distribution requests.

####
address_please(Name, Host, AddressFamily) ->
Success | {error, term()}
OTP 21.0

### Types

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 to resolves the Host to an IP address of a remote node.

As an optimization this function may also return the port and version of the remote node. If port and version are returned port_please/3 will not be called.

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names(Host) -> {ok, [{Name, Port}]} | {error, Reason}
OTP 21.0

### Types

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.

Example:

    (arne@dunn)1> erl_epmd:names(localhost).
    {ok,[{"arne",40262}]}