[erlang-questions] net_kernel:start() "the name seems to be in use by another Erlang node"

Mon Jan 29 13:47:22 CET 2018


1. if you use longnames, you must _use_ a long name
2. epmd must be running 

Eshell V9.2  (abort with ^G)
1> net_kernel:start([foo,longnames]).

=INFO REPORT==== 29-Jan-2018::12:11:46 ===
Can't set long node name!
Please check your configuration
2> net_kernel:start(['foo@REDACTED',longnames]).

=INFO REPORT==== 29-Jan-2018::12:12:07 ===
Protocol 'inet_tcp': register/listen error: econnrefused

>From epmd documentation:
The daemon is started automatically by command erl(1) if the node is to
be distributed and no running instance is present.

Since we didn’t start the node so, it's not auotmatic. In fact
me@REDACTED ~ $ ps -ef | grep epmd
me      2439  2422  0 12:12 pts/2    00:00:00 grep --colour=auto epmd

If you start a node with distribution, and kill it immediately, epmd
will have started:
me@REDACTED ~ $ erl -sname foo
Erlang/OTP 20 [erts-9.2] [source] [64-bit] [smp:2:2] [ds:2:2:10]
[async-threads:10] [hipe] [kernel-poll:false]

Eshell V9.2  (abort with ^G)
User switch command
 --> q
me@REDACTED ~ $ ps -ef | grep epmd
me      2454  1521  0 12:19 ?        00:00:00
/usr/local/lib/erlang/erts-9.2/bin/epmd -daemon
me      2524  2422  0 12:20 pts/2    00:00:00 grep --colour=auto epmd

So now you can attempt starting the node again:
3> net_kernel:start(['foo@REDACTED',longnames]).

Also, net_kernel:start/1 does not return {already_started, pid()}, but
{error, Reason} and Reason _could_ be {already_started, pid()}.

If you now try to start another node in the same way with the same name,
you will get the error you are getting:

1> net_kernel:start(['foo@REDACTED',longnames]).

=INFO REPORT==== 29-Jan-2018::13:45:13 ===
Protocol 'inet_tcp': the name foo@REDACTED seems to be in use by
another Erlang node


Date: Mon, 29 Jan 2018 17:57:09 +0900
From: zxq9@REDACTED
To: erlang-questions@REDACTED
Subject: Re: [erlang-questions] net_kernel:start() "the name seems to
	be in	use by another Erlang node"
Message-ID: <28099967.CzVN9HJnuF@REDACTED>
Content-Type: text/plain; charset="UTF-8"

On 2018?1?28???? 15?51?07? JST Mark Sebald wrote:
> I am using "net_kernel:start()", to start multiple nodes of the same 
> application, on the same host. Each time I start a node, I don't know 
> how many other nodes were already started, so my thinking was to add 
> an index number to the node name, and if start() returns: "{already_started, pid()}"
> I will increment the index on the node name, and call start() again.
> Instead, when I try to start a second node of the same name I get this:
> 14:14:29.425 [info] Protocol 'inet_tcp': the name my_node01@REDACTED 
> seems to be in use by another Erlang node
> 14:14:29.425 [error] CRASH REPORT Process <0.109.0> with 0 neighbours 
> exited with reason: {error,badarg} in gen_server:init_it/6 line 349
> and an error tuple is returned
> This seems like an Erlang bug, since the info log message indicates 
> that the situation is well in hand, but then we get a crash.  Is there 
> a better way to start multiple nodes?  Are there any conditions where 
> start() will return "already_started"?

I've not messed with this in a while, but I do recall being able to do
dynamic start names like this. I don't have a sample of the code that
did it for me, though.

In the shell, however, the following worked.

Node 1:

  Eshell V9.2  (abort with ^G)
  1> net_kernel:start([foo, longnames]).

Node 2:

  Eshell V9.2  (abort with ^G)
  1> Start = 
  1>   fun(Name1, Name2) ->
  1>     case net_kernel:start([Name1, longnames]) of
  1>       {ok, Pid} ->
  1>         {ok, Pid};
  1>       {error, Reason} ->
  1>         ok = io:format("Failed with ~tp~nTrying ~tp~n", [Reason,
  1>         net_kernel:start([Name2, longnames])
  1>     end
  1>   end.
  2> Start(foo, bar).
  Failed with {{shutdown,
  Trying bar
  =INFO REPORT==== 29-Jan-2018::17:48:11 ===
  Protocol 'inet_tcp': the name foo@REDACTED seems to
be in use by another Erlang node

The info message from SASL still pops up, but it isn't crashing
anything, just returning the error tuple as expected. I'm not sure what
else would be going on in your case. I know there are a few tricky EPMD
issues, I just never seem to run into them.


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