Some Linux distributions don't come bundled with the ca-certificates and gnupg2 packages. If you use such a distribution, you'll need to install them with:
This example is for Debian/Ubuntu and derivatives. Consult your distribution's documentation if you use another one.
Some users have reported that they can't download the key from Ubuntu's keyserver. When they run the gpg command, their firewalls or proxies block their requests to download. If this issue affects you, you can try this alternative:
Distributions like Amazon Linux 2 and CentOS before version 8 don't support the PGP V4 signature we use. You'll need to disable the verification when you install k6: