I have a simple gen_server which connects to a tcp port, when I run gen_server directly:
erl -noshell -s ttest start
it works fine, But when I run:
erl -noshell -s tt_sup start_link
the connection will be closed instantly, It will work if I unlink the supervisor:
erl -noshell -s tt_sup start_shell
How could I run my simple gen_tcp:connect (gen_server) with supervisor ?
Supervisor :

-module(tt_sup).
-behaviour(supervisor).
-export([init/1, start_link/0, start_shell/0]).

start_link() ->
    io:format("Supervisor started with PID~p~n", [self()]),
    {ok, Pid} = supervisor:start_link(tt_sup, []),
    io:format("Supervisor PID=~p~n", [Pid]),
    {ok, Pid}.

start_shell() ->
    io:format("Supervisor started with PID~p~n", [self()]),
    {ok, Pid} = supervisor:start_link(tt_sup, []),
    io:format("Supervisor PID=~p~n", [Pid]),
    unlink(Pid),
    {ok, Pid}.

init(_Args) ->
    SupFlags = #{strategy => one_for_one},
    Child = [#{id => ttest, start => {ttest, start, []},
               restart => permanent, shutdown => brutal_kill,
               type => worker, modules => [ttest]}],
    {ok, {SupFlags, Child}}.

gen_server:

-module(ttest).
-export([start/0,init/1,handle_cast/2,handle_call/3,handle_info/2,terminate/2,connect/1]).
-behaviour(gen_server).


start() ->

       io:format("gen_server start id is ~p~n",[self()]),
       {ok,Pid} = gen_server:start_link({local,ttest},ttest,[],[]),
       io:format("gen_server id is ~p~n",[Pid]),
       connect(Pid),
       {ok,Pid}.


init(_Args) ->
        io:format("init id is ~p~n",[self()]),
        {ok,[]}.       
handle_call({tcp,Socket,Bin},_From,States) ->
        {reply,States,States}.
handle_info({tcp,Socket,Bin},States) ->
        io:format("got info msg"),
        {noreply,States}.

handle_cast({send,Msg},States) ->
        {reply,States}.

connect(I) ->
    io:format("connect id is ~p~n",[self()]),
    {ok,Socket} =gen_tcp:connect("localhost",6000,[binary,{active,true}]),
    gen_tcp:controlling_process(Socket,I).


terminate(shutdown, State) ->
    io:format("terminating"),
    ok.