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

[arif@REDACTED]

Sorry, I forgot to add that you will get the error {already_started,
pid()} if you try to start the node from the already started node:

(foo@REDACTED)4>
net_kernel:start(['foo@REDACTED',longnames]).
{error,{already_started,<0.73.0>}}
(foo@REDACTED)5> 
 
BR/Arif

On 2018-01-29 13:47, arif@REDACTED wrote:
> Hi, 
> 
> 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
> {error,
>     {{shutdown,
>          {failed_to_start_child,net_kernel,{'EXIT',nodistribution}}},
>      {child,undefined,net_sup_dynamic,
>          {erl_distribution,start_link,[[foo,longnames],false]},
>          permanent,1000,supervisor,
>          [erl_distribution]}}}
> 2> net_kernel:start(['foo@REDACTED',longnames]).
> 
> =INFO REPORT==== 29-Jan-2018::12:12:07 ===
> Protocol 'inet_tcp': register/listen error: econnrefused
> {error,
>     {{shutdown,
>          {failed_to_start_child,net_kernel,{'EXIT',nodistribution}}},
>      {child,undefined,net_sup_dynamic,
>          {erl_distribution,start_link,
>              [['foo@REDACTED',longnames],false]},
>          permanent,1000,supervisor,
>          [erl_distribution]}}}
> 
> 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)
> (foo@REDACTED)1> 
> (foo@REDACTED)1> 
> 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
> me@REDACTED ~ $
> 
> So now you can attempt starting the node again:
> 3> net_kernel:start(['foo@REDACTED',longnames]).
> {ok,<0.73.0>}
> (foo@REDACTED)4>
> 
> 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
> {error,
>     {{shutdown,
>          {failed_to_start_child,net_kernel,{'EXIT',nodistribution}}},
>      {child,undefined,net_sup_dynamic,
>          {erl_distribution,start_link,
>              [['foo@REDACTED',longnames],false]},
>          permanent,1000,supervisor,
>          [erl_distribution]}}}
> 2> 
> 
> BR/Arif
> 
> 
> 
> 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]).
>   {ok,<0.66.0>}
>   (foo@REDACTED)2>
> 
> 
> 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,
> Name2]),
>   1>         net_kernel:start([Name2, longnames])
>   1>     end
>   1>   end.
>   #Fun<erl_eval.12.99386804>
>   2> Start(foo, bar).
>   Failed with {{shutdown,
>                   
> {failed_to_start_child,net_kernel,{'EXIT',nodistribution}}},
>                {child,undefined,net_sup_dynamic,
>                   
> {erl_distribution,start_link,[[foo,longnames],false]},
>                    permanent,1000,supervisor,
>                    [erl_distribution]}}
>   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
>   {ok,<0.71.0>}
>   (bar@REDACTED)3>
> 
> 
> 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.
> 
> -Craig