apt update
Hit:1 http://archive.canonical.com/ubuntu focal InRelease
Ign:2 http://archive.ubuntu.com/ubuntu-archive focal InRelease
Ign:3 http://archive.ubuntu.com/ubuntu-archive focal-updates InRelease
Ign:4 http://archive.ubuntu.com/ubuntu-archive focal-backarchive InRelease
Ign:5 http://archive.ubuntu.com/ubuntu-archive focal-security InRelease
Err:6 http://archive.ubuntu.com/ubuntu-archive focal Release
  404  Not Found [IP: 91.189.88.152 80]
Err:7 http://archive.ubuntu.com/ubuntu-archive focal-updates Release
  404  Not Found [IP: 91.189.88.152 80]
Err:8 http://archive.ubuntu.com/ubuntu-archive focal-backarchive Release
  404  Not Found [IP: 91.189.88.152 80]
Err:9 http://archive.ubuntu.com/ubuntu-archive focal-security Release
  404  Not Found [IP: 91.189.88.152 80]
Reading package lists... Done
E: The repository 'http://archive.ubuntu.com/ubuntu-archive focal Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://archive.ubuntu.com/ubuntu-archive focal-updates Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://archive.ubuntu.com/ubuntu-archive focal-backarchive Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://archive.ubuntu.com/ubuntu-archive focal-security Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
root@localhost:/etc/apt# apt upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.