code: function(command, host, options, cb) {
    let child = null;
  
    if(env === Constants.RESERVED.ENV_DEV) {
      child = cp.spawn(command, options);
      let prefix = command === Constants.COMMAND.SSH ? '[' + host + '] ' : '';
  
      child.stderr.on('data', function (chunk) {
        let msg = chunk.toString();
        process.stderr.write(msg);
        if(!!cb) {
          cb(msg);
        }
      });
  
      child.stdout.on('data', function (chunk) {
        let msg = prefix + chunk.toString();
        process.stdout.write(msg);
      });
    } else {
      child = cp.spawn(command, options, {detached: true, stdio: 'inherit'});
      child.unref();
    }
  
    child.on('exit', function (code) {
      if(code !== 0) {
        logger.warn('child process exit with error, error code: %s, executed command: %s', code,  command);
      }
      if (typeof cb === 'function') {
        cb(code === 0 ? null : code);
      }
    });
  }
docs: Fork child process to run command.
  
  @param {String} command
  @param {Object} options
  @param {Callback} callback