apt-get update 오류1

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  [ubuntu] apt-get 오류 / ubuntu 18.04 LTS sudo apt-get update 명령어를 실행했는데 언젠가 부터 아래와 같은 오류가 남. Err:1 http://ppa.launchpad.net/certbot/certbot/ubuntu bionic InRelease Temporary failure resolving 'ppa.launchpad.net' Err:2 http://archive.ubuntu.com/ubuntu bionic InRelease Temporary failure resolving 'archive.ubuntu.com' Err:3 http://dl.google.com/linux/chrome/deb stable InRelease Temporary failure resolving 'dl.google.com' Err:4 http://arch.. OS/ubuntu 2020. 3. 3.