When yum is installed, it prompts "No GPG public key has been installed, please download and install the software signature public key you want to install"

• In the CentOS 7.7 operating system, when installing oracle's dependency package, it appears that no GPG public key has been installed yet, and it is required to use rpm --import public.gpg.key to import
  
• Under normal circumstances, the GPG KEY will be available in the system, in the directory of your Linux installation CD, or in the /etc/pki/rpm-gpg/ directory, for example, my system is in the /etc/pki/rpm-gpg/ directory Next, there is a RPM-GPG-KEY-CentOS-7
  
• The solution is to use the command in the prompt to import the
  rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7. After the
  execution is complete, use yum to install the oracle dependency package, and then Can be installed normally