When run apt update,
root@hadoop123:~# apt-get update
Get:5 https://repo.saltproject.io/py3/ubuntu/20.04/amd64/archive/3005 focal InRelease [2125 B]
Err:5 https://repo.saltproject.io/py3/ubuntu/20.04/amd64/archive/3005 focal InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0E08A149DE57BFBE
Reading package lists... Done
W: GPG error: https://repo.saltproject.io/py3/ubuntu/20.04/amd64/archive/3005 focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0E08A149DE57BFBE
E: The repository 'https://repo.saltproject.io/py3/ubuntu/20.04/amd64/archive/3005 focal InRelease' is not signed.
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@hadoop123:~# sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 0E08A149DE57BFBE
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
Executing: /tmp/apt-key-gpghome.LJUVq0TIDD/gpg.1.sh --keyserver keyserver.ubuntu.com --recv-keys 0E08A149DE57BFBE
gpg: key 0E08A149DE57BFBE: "SaltStack Packaging Team <packaging@saltstack.com>" not changed
gpg: Total number processed: 1
gpg: unchanged: 1
Solution:
apt-get clean
cd /var/lib/apt
mv lists lists.old
mkdir -p lists/partial
apt-get clean
apt-get update