docs: function checkPid(pid, callback) {
    var list, msg = '';
    var isWin = _.isWin();
    var serverInfo = util.serverInfo() || options;
  
    if (isWin) {
      list = spawn('tasklist');
    } else {
      list = spawn('ps', ['-A']);
    }
  
    list.stdout.on('data', function(chunk) {
      msg += chunk.toString('utf-8').toLowerCase();
    });
  
    list.on('exit', function() {
      var found = false;
      msg.split(/[\r\n]+/).forEach(function(item) {
  
        if (~item.indexOf('--type ' + serverInfo.type) || process.platform !== 'darwin') {
          var m = item.match(/\d+/);
  
          if (m && m[0] == pid) {
            found = true;
          }
        }
      });
  
      callback(found);
    });
  
    list.on('error', function(e) {
      if (isWin) {
        fis.log.error('fail to execute `tasklist` command, please add your system path (eg: C:\\Windows\\system32, you should replace `C` with your system disk) in %PATH%');
      } else {
        fis.log.error('fail to execute `ps` command.');
      }
    });
  }