After executing sudo apt-get update in a Azure VM I receive this output:
Hit:1 http://packages.microsoft.com/repos/vscode stable InRelease
Hit:2 http://ppa.launchpad.net/webupd8team/atom/ubuntu xenial InRelease
Hit:3 http://azure.archive.ubuntu.com/ubuntu xenial InRelease
Get:4 http://apt-mo.trafficmanager.net/repos/dotnet-release xenial InRelease [2835 B]
Get:5 http://azure.archive.ubuntu.com/ubuntu xenial-updates InRelease [102 kB]
Get:6 http://azure.archive.ubuntu.com/ubuntu xenial-backports InRelease [102 kB]
Hit:7 http://ppa.launchpad.net/x2go/stable/ubuntu xenial InRelease
Err:1 http://packages.microsoft.com/repos/vscode stable InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY EB3E94ADBE1229CF
Hit:8 https://packages.microsoft.com/ubuntu/16.04/prod xenial InRelease
Ign:9 https://dl.bintray.com/sbt/debian InRelease
Hit:10 https://download.docker.com/linux/ubuntu xenial InRelease
Err:2 http://ppa.launchpad.net/webupd8team/atom/ubuntu xenial InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C2518248EEA14886
Get:11 https://dl.bintray.com/sbt/debian Release [815 B]
Get:12 http://security.ubuntu.com/ubuntu xenial-security InRelease [102 kB]
Hit:11 https://dl.bintray.com/sbt/debian Release
Get:13 http://azure.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages [724 kB]
Get:14 http://azure.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 Packages [587 kB]
Err:7 http://ppa.launchpad.net/x2go/stable/ubuntu xenial InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7CDE3A860A53F9FD
Err:8 https://packages.microsoft.com/ubuntu/16.04/prod xenial InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY EB3E94ADBE1229CF
Fetched 1621 kB in 0s (2135 kB/s)
Reading package lists... Done
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://packages.microsoft.com/repos/vscode stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY EB3E94ADBE1229CF
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://ppa.launchpad.net/webupd8team/atom/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C2518248EEA14886
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://ppa.launchpad.net/x2go/stable/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7CDE3A860A53F9FD
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://packages.microsoft.com/ubuntu/16.04/prod xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY EB3E94ADBE1229CF
W: Failed to fetch https://packages.microsoft.com/ubuntu/16.04/prod/dists/xenial/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY EB3E94ADBE1229CF
W: Failed to fetch http://packages.microsoft.com/repos/vscode/dists/stable/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY EB3E94ADBE1229CF
W: Failed to fetch http://ppa.launchpad.net/webupd8team/atom/ubuntu/dists/xenial/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C2518248EEA14886
W: Failed to fetch http://ppa.launchpad.net/x2go/stable/ubuntu/dists/xenial/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7CDE3A860A53F9FD
W: Some index files failed to download. They have been ignored, or old ones used instead.
I saw many similar issues here or googling, but none of them is actually working for me and I still receive the reported error.
Feel free to ask for more details, if you think it is duplicated, please report me the link
