Fix Docker installation NO_PUBKEY error on Ubuntu 20.04 LTS

Today we are going to Fix Docker installation NO_PUBKEY error on Ubuntu 20.04 LTS and Debian 11 Bullseye

If you getting the below error message when running the below command for installing docker and Kubernetes in Ubuntu 20.04 LTS server.

root@linuxstoney:/home/ubuntu# add-apt-repository \
>   "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
>   $(lsb_release -cs) \
>   stable"
Hit:1 http://in.archive.ubuntu.com/ubuntu bionic InRelease
Get:2 https://download.docker.com/linux/ubuntu bionic InRelease [64.4 kB]
Hit:3 http://in.archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit:4 http://in.archive.ubuntu.com/ubuntu bionic-backports InRelease
Hit:5 http://in.archive.ubuntu.com/ubuntu bionic-security InRelease
**Err:2 https://download.docker.com/linux/ubuntu bionic InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7EA0A9C3F273FCD8**
Reading package lists... Done
W: GPG error: https://download.docker.com/linux/ubuntu bionic 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 bionic 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@linuxstoney:/home/ubuntu#

even if you have also run the below command but no luck ;

root@linuxstoney:/# sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 7EA0A9C3F273FCD8
Executing: /tmp/apt-key-gpghome.rDOuMCVLF2/gpg.1.sh --keyserver keyserver.ubuntu.com --recv-keys 7EA0A9C3F273FCD8
gpg: keyserver receive failed: No keyserver available

Check and Find Out How Long Time Take To Boot Your Linux System

Solution is Run this to add the correct key:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu focal stable"

Source: https://docs.docker.com/install/linux/docker-ce/ubuntu/

if you facing Docker error issue with Debian 11 Testing (bullseye):

Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).

But can be solved with:

 curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /us