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# net_adm

### MODULE

net_adm

### MODULE SUMMARY

Various Erlang Net Administration Routines

### DESCRIPTION

This module contains various network utility functions.

### EXPORTS

dns_hostname(Host) -> {ok, Name} | {error, Host}

Types:

Host = atom() | string()
Name = string()

Returns the official name of Host, or {error, Host} if no such name is found. See also inet(3).

host_file() -> Hosts | {error, Reason}

Types:

Hosts = [Host :: atom()]
Reason = file:posix()
| badarg
| terminated
| system_limit
| {Line :: integer(), Mod :: module(), Term :: term()}

Reads the .hosts.erlang file, see the section Files below. Returns the hosts in this file as a list, or returns {error, Reason} if the file could not be read or the Erlang terms on the file could not be interpreted.

localhost() -> Name

Types:

Name = string()

Returns the name of the local host. If Erlang was started with the -name command line flag, Name is the fully qualified name.

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

Types:

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

Similar to epmd -names, see epmd(1). Host defaults to the local host. Returns the names and associated port numbers of the Erlang nodes that epmd at the specified host has registered.

Returns {error, address} if epmd is not running.

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

ping(Node) -> pong | pang

Types:

Node = atom()

Tries to set up a connection to Node. Returns pang if it fails, or pong if it is successful.

world() -> [node()]
world(Arg) -> [node()]

Types:

Arg = verbosity()
verbosity() = silent | verbose

This function calls names(Host) for all hosts which are specified in the Erlang host file .hosts.erlang, collects the replies and then evaluates ping(Node) on all those nodes. Returns the list of all nodes that were, successfully pinged.

Arg defaults to silent. If Arg == verbose, the function writes information about which nodes it is pinging to stdout.

This function can be useful when a node is started, and the names of the other nodes in the network are not initially known.

Failure: {error, Reason} if host_file() returns {error, Reason}.

world_list(Hosts) -> [node()]
world_list(Hosts, Arg) -> [node()]

Types:

Hosts = [atom()]
Arg = verbosity()
verbosity() = silent | verbose

As world/0,1, but the hosts are given as argument instead of being read from .hosts.erlang.

### Files

The .hosts.erlang file consists of a number of host names written as Erlang terms. It is looked for in the current work directory, the user's home directory, and $OTP_ROOT (the root directory of Erlang/OTP), in that order.

The format of the .hosts.erlang file must be one host name per line. The host names must be within quotes as shown in the following example:

    'super.eua.ericsson.se'.
    'renat.eua.ericsson.se'.
    'grouse.eua.ericsson.se'.
    'gauffin1.eua.ericsson.se'.
    ^ (new line)