title: Docker: How to solve the public key error in ubuntu while installing docker
body: <p>I am getting the below error message when running the below command for installing docker and kubernetes in Ubuntu server. </p>
  
  <pre><code>root@master:/home/ubuntu# add-apt-repository \
  &gt;   "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
  &gt;   $(lsb_release -cs) \
  &gt;   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@master:/home/ubuntu#
  </code></pre>
  
  <p>I have also ran the below command but no luck</p>
  
  <pre><code>root@master:/# 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
  </code></pre>