Signatures couldn't be verified because the public key is not available: NO_PUBKEY

[anjumfarzana]

When i run the commands for Ubuntu 20.04 Build: https://carla.readthedocs.io/en/0.9.14/build_linux/#unreal-engine.

sudo apt-add-repository "deb http://apt.llvm.org/focal/ llvm-toolchain-focal main"

I got below error:
Err:14 https://apt.llvm.org/focal llvm-toolchain-focal InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY xxxxxxxxxxx
Reading package lists... Done
W: GPG error: https://apt.llvm.org/focal llvm-toolchain-focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 15CF4D18AF4F7421
E: The repository 'http://apt.llvm.org/focal llvm-toolchain-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

I am using Ubuntu 20.04 version

Please help to solve this issue?

Thank You!

[jimmysoda]

@anjumfarzana I just came across this problem. This preceding step appears to be missing from the documentation:

wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -

See https://askubuntu.com/a/906366.