sudo apt-get update sudo apt-get update를 입력하고 아래와 같은 GPG error가 발생하는 경우가 있습니다. W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://packages.ros.org/ros/ubuntu bionic InRelease: The following signatures were invalid: EXPKEYSIG F42ED6FBAB17C654 Open Robotics W: Failed to fetch http://packages.ros.org/ros..