I am getting the below error message when running the below command for installing docker and kubernetes in Ubuntu server.
root@master:/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 InReleaseGet:2 https://download.docker.com/linux/ubuntu bionic InRelease [64.4 kB]Hit:3 http://in.archive.ubuntu.com/ubuntu bionic-updates InReleaseHit:4 http://in.archive.ubuntu.com/ubuntu bionic-backports InReleaseHit: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... DoneW: 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#I have also ran the below command but no luck
root@master:/# sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 7EA0A9C3F273FCD8Executing: /tmp/apt-key-gpghome.rDOuMCVLF2/gpg.1.sh --keyserver keyserver.ubuntu.com --recv-keys 7EA0A9C3F273FCD8gpg: keyserver receive failed: No keyserver available