Problems with starting an erlang application from the command line

Question

I am trying to start an application form the command line. The application is basically a OTP compliant TCP server and it works fine when started from the shell. However, when started form the command line it actually does not start.

I have all files in a compliant folder structure, meaning sources in \src and binaries \ebin. I have set the path in the .erlang file with

code:add_patha("./ebin").

And the function that is being called is in this module

-module(wotsuke_geolocation_lookup_server).
-behaviour(application).

-export([start/0, start/2, stop/1]).

start() -> 
    event_dbs:start(),
    wotsuke_server_sup:start_link().

start(_Type, _Args) ->
    event_dbs:start(),
    wotsuke_server_sup:start_link().

stop(_State) ->
    ok.

I have added (redundantly) also a start/0 (i use a start/2 due to future features requiring the args) because starting with arguments never worked. Now when I run:

erl -run wotsuke_geolocation_lookup_server start [] []

I get

Erlang/OTP 18 [erts-7.0] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false]

{"init terminating in do_boot",{undef,[{wotsuke_geolocation_lookup_server,start,[["[]","[]"]],[]},{init,start_it,1,[]},{init,start_em,1,[]}]}}

Crash dump is being written to: erl_crash.dump...done
init terminating in do_boot ()

Meaning it cannot find the module/function. Therefore, I used the redundant start/0

erl -run wotsuke_geolocation_lookup_server start

and get:

Erlang/OTP 18 [erts-7.0] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false]

Eshell V7.0  (abort with ^G)
1>

Basically nothing is started (no process ID returned). I tried to connect to the server and get the typical answer when the server is off. I also tried by forcing erl to the ebin folder with the -pa option. Same as above.

As a this is the first time I am trying to run an erlang app from the command line (in order to demonize it), I am left clueless.

Thanks for any help.

ADDED: not sure it helps, I add the erlang app code as well

{application, wotsuke_geolocation_lookup_server,
   [{description, "Wotsuke Geolocation lookup server"},
    {vsn, "0.1.0"},
    {modules, [tcpserver_otp_backend, ets_methods, data_packing, data_formats, event_timings, logger, event_dbs,
                    obsolete_data_clean_ad, obsolete_data_clean, wotsuke_data_input, wotsuke_logger, wotsuke_server_sup, data_retrieve, wotsuke_data_output, user_event_dbs,
                    event_areas]},
    {registered, [wotsuke_data_input, wotsuke_server_sup, wotsuke_logger, wotsuke_data_output]},
    {applications, [kernel, stdlib, mnesia]},
    {env, []},
    {mod, {bsc, []}}]}.

UPDATE: One issue is solved. The issue with the command

erl -run wotsuke_geolocation_lookup_server start [] []

is actually due t the fact that erl expects either a start/0 is only the module is specified or arity 1 if the function is also specified. Making [] [] to be seen as [[],[]].

looks like it is picking erl -run wotsuke_geolocation_lookup_server start [] [] up as one argument as {"init terminating in do_boot",{undef,[{wotsuke_geolocation_lookup_server,start,[["[]","[]"]],[]},{init,start_it,1,[]},{init,start_em,1,[]}]}} means undef for start/1 as ["[]","[]"] is one argument — ernstroux

Francesco Francesco · Accepted Answer · 2017-05-11T08:04:29

Clearly my problem is due to the fact that a supervisor cannot be started via the command line as a standard function but by using application:start. Therefore, I have solved my problem by using the application as such and execute on command line

erl (options) eval "application:start(...)"

Problems with starting an erlang application from the command line

2 Answers