luaposix msgget函数不会创建队列

Question

我正在玩luaposix模块（使用luajit）试图学习如何分叉进程并将其妖魔化。以下是创建新进程并尝试设置msg队列以与子进行通信的代码。我使用函数msgget（key）来创建队列但是函数出错了“没有这样的文件或目录”，请有人帮我理解错误在哪里？

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()