luaposix msgget function doesn't create the queue

Question

I'm playing with luaposix module (using luajit) trying to learn how to fork process and demonize it. Here is the code that create a new process and try to set up a msg queue for communication with the child. I use the function msgget(key) to create the queue but the function goes in error with "No such file or directory", please can someone help me to understand where is the mistake ?

local psx = require("posix");
local os = require("os");

--daemon sleep before die
local DAEMON_SLEEP_BD = 20;
--sleep seconds in write
local SLEEP_SEC = 1;
--message que key
local MSGQ_KEY = 1000;


function main()
  local ppid = nil;
  local pid = nil;
  local sid = nil;

  --clear screen
  os.execute("clear");

  --get process pid - this is the parent
  ppid = psx.getpid ("pid"); 

  psx.sleep(SLEEP_SEC);
  io.write("proces started with pid : "..ppid.."\n");
  psx.sleep(SLEEP_SEC);

  --create a msq queque
  psx.sleep(SLEEP_SEC);
  io.write("process "..ppid.." is going to create a msg queue...\n");
  psx.sleep(SLEEP_SEC);

  local msgqid = psx.msgget(MSGQ_KEY,psx.IPC_CREATE);

  if msgqid==nil then
    psx.sleep(SLEEP_SEC);
    io.write(psx.errno().."\n");
    io.write("process "..ppid.." failed to create msg queue...stopping execution\n") ;
    psx.sleep(SLEEP_SEC); 

    psx._exit(-1);
  end

  psx.sleep(SLEEP_SEC); 
  io.write("process "..ppid.." created msg que with identifier "..msgqid.."\n");
  psx.sleep(SLEEP_SEC); 

  psx.sleep(SLEEP_SEC);
  io.write("process "..ppid.." is going to fork\n");
  psx.sleep(SLEEP_SEC);

  pid = psx.fork(); 

  if pid < 0 then
    psx.sleep(SLEEP_SEC);
    io.write("process " ..ppid.." failed to fork...stopping execution\n")
    psx.sleep(SLEEP_SEC);

    psx._exit(-1);
  end

  if pid > 0 then
    --##################################################
    --here put the code of parent process after the fork
    --##################################################

    psx.sleep(SLEEP_SEC);
    io.write("process "..ppid.." is going to wait msg from forked child\n");
    psx.sleep(SLEEP_SEC);

    while true do
      psx.sleep(SLEEP_SEC);
      io.write("process "..ppid.." waiting for msg from forked process.\n");
      psx.sleep(SLEEP_SEC);

      local msg_type, msg_text = psx.msgrcv(msgqid,1,100)

      if msg_type == nil then 
        psx.sleep(SLEEP_SEC);
        io.write("process " ..ppid.." raised error receiving msg...stopping execution\n");
        psx.sleep(SLEEP_SEC);

        psx._exit(-1);
      end

      if msg_text == "ok" then
        psx.sleep(SLEEP_SEC);
        io.write("process "..ppid.." received mesg from forked "..msg_text.." stopping execution to demonaze\n");
        psx.sleep(SLEEP_SEC);

        psx.sleep(SLEEP_SEC);
        io.write("process "..ppid.." die letting fork to demonize\n");
        psx.sleep(SLEEP_SEC);

        psx._exit(0);
      end

    end --while  

  end --if

  --#################################################################
  --here write the code of child process that will setup it as daemon
  --#################################################################

  pid = psx.getpid("pid");

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." born from fork is the candidate daemon...\n");
  psx.sleep(SLEEP_SEC);

  psx.sleep(SLEEP_SEC);
  io.write(str.format("process "..pid.." eredited db env %s \n",envv));
  psx.sleep(SLEEP_SEC);

  psx.sleep(SLEEP_SEC);
  io.write(str.format("process "..pid.." eredited db connection %s \n",con));
  psx.sleep(SLEEP_SEC);

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." changing umask\n");
  psx.sleep(SLEEP_SEC);

  psx.umask(0);

  --open log for writing --to_do

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." changing setsid...\n");
  psx.sleep(SLEEP_SEC);

  sid = psx.setpid("s");

  if sid ==nill then
    psx.sleep(SLEEP_SEC);
    io.write("process "..pid.." setsid failed\n");
    psx.sleep(SLEEP_SEC);

    psx._exit(-1);
  end

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." candidate daemon sid :"..sid.."\n");  
  psx.sleep(SLEEP_SEC);

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." changing working directory.\n");
  psx.sleep(SLEEP_SEC);

  if psx.chdir("/")==nill then
    psx.sleep(SLEEP_SEC);
    io.write(".....can't change the dir\n");
    psx.sleep(SLEEP_SEC);

    psx._exit(-1);
  end

  psx.sleep(SLEEP_SEC);
  io.write("process " ..pid.." changed directory to "..psx.getcwd().."\n");
  psx.sleep(SLEEP_SEC);

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." attaching parent message queue with msgq_key "..MSGQ_KEY.."\n");
  psx.sleep(SLEEP_SEC);

  --attach the msg que using the same key
  msgqid = psx.msgget(MSGQ_KEY); 
  if msgqid == nill then
    psx.sleep(SLEEP_SEC);
    io.write("process "..pid.." attaching msgq failed...stopping execution\n");
    psx.sleep(SLEEP_SEC);

    psx._exit(-1);
  end

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." has attached msq queue with msgid "..msgqid.."\n");
  psx.sleep(SLEEP_SEC);

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." going to close all file descriptor now is a daemon\n");
  psx.sleep(SLEEP_SEC);

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." entering in while loop.\n");
  psx.sleep(SLEEP_SEC);

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." sending msg to parent telling him to die\n");
  psx.sleep(SLEEP_SEC);

  if psx.msgsnd(msgqid,1,"ok")==nil then
    psx.sleep(SLEEP_SEC);
    io.write("process "..pid.." raised error sending msg...stopping execution.\n");
    psx.sleep(SLEEP_SEC);
  end

  psx.sleep(SLEEP_SEC);
  io.write("process "..pid.." msg sent\n");
  psx.sleep(SLEEP_SEC);



  psx.close(0);
  psx.close(1);
  psx.close(2);

  while true do
    --here write the code of daemon
    --you can't use io.write/print because fd are closed

    psx.sleep(DAEMON_SLEEP_BD)
    psx._exit(0); 

  end --while



end --main

main()