apt-get update failed?

Question

Get:1 https://download.docker.com/linux/ubuntu focal InRelease [36.2 kB]
Err:1 https://download.docker.com/linux/ubuntu focal InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7EA0A9C3F273FCD8
Ign:2 http://old-releases.ubuntu.com/ubuntu focal-security InRelease
Err:3 http://old-releases.ubuntu.com/ubuntu focal-security Release
  404  Not Found [IP: 91.189.91.124 80]
Err:4 http://in.old-releases.ubuntu.com/ubuntu focal-backports InRelease
  Could not resolve 'in.old-releases.ubuntu.com'
Reading package lists...
W: GPG error: https://download.docker.com/linux/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7EA0A9C3F273FCD8
E: The repository 'https://download.docker.com/linux/ubuntu focal InRelease' is not signed.
E: The repository 'http://old-releases.ubuntu.com/ubuntu focal-security Release' does not have a Release file.
W: Target Packages (stable/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:60
W: Target Translations (stable/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:60
W: Target Translations (stable/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:60
W: Target DEP-11 (stable/dep11/Components-amd64.yml) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:60
W: Target DEP-11 (stable/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:60
W: Target CNF (stable/cnf/Commands-amd64) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:60
W: Target CNF (stable/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:60
W: Target Packages (stable/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:62
W: Target Translations (stable/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:62
W: Target Translations (stable/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:62
W: Target DEP-11 (stable/dep11/Components-amd64.yml) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:62
W: Target DEP-11 (stable/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:62
W: Target CNF (stable/cnf/Commands-amd64) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:62
W: Target CNF (stable/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:62
W: Target Packages (stable/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:64
W: Target Translations (stable/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:64
W: Target Translations (stable/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:64
W: Target DEP-11 (stable/dep11/Components-amd64.yml) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:64
W: Target DEP-11 (stable/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:64
W: Target CNF (stable/cnf/Commands-amd64) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:64
W: Target CNF (stable/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:64
W: Target Packages (stable/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:66
W: Target Translations (stable/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:66
W: Target Translations (stable/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:66
W: Target DEP-11 (stable/dep11/Components-amd64.yml) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:66
W: Target DEP-11 (stable/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:66
W: Target CNF (stable/cnf/Commands-amd64) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:66
W: Target CNF (stable/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:58 and /etc/apt/sources.list:66

Answer 1

You have some weird repositories enabled. Why are you using old-releases.ubuntu.com with Ubuntu 20.04? This repository is only for old unsupported versions of Ubuntu. Also, one line says in.old-releases.ubuntu.com which doesn't exist.

I recommend replacing your /etc/apt/sources.list with "default" one for 20.04:

deb http://archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse

deb http://archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse

deb http://archive.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse

deb http://archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse

deb http://archive.canonical.com/ubuntu focal partner
deb-src http://archive.canonical.com/ubuntu focal partner

You'll need to re-add the docker repository, but this should fix the update issue with old-releases.ubuntu.com.

Answer 2

I just used this command and it solved the problem

# rm -rf /var/lib/apt/lists/*

then

# apt-get update