Recently I faced with the problem that Git client for Linux (CentOS) always asked for user credentials on every push even though SSH key was installed. In general SSH key is installed exactly for avoiding that. So what went wrong?
Let's briefly check whole process. First of all we need to install SSH key pair. On Linux it can be done with ssh-keygen tool. If you don't want to enter passphrase on every push just click Enter on each step. By default it will save public/private key files (id_rsa.pub and id_rsa) into ~/.ssh folder (where ~ means local user folder - usually under /home/local/...). After that copy content of public key file id_rsa.pub and go GitHub > your profile Settings > SSH and GPG keys > SSH keys and paste content there:
Installation of SSH key has been completed. But if you will try to clone some repository and try to push changes there (assuming that you have write permission in this repository) git may still ask for username/pw credentials and every push. As it turned out it depends on how repository was cloned. There are several ways to clone repositories: HTTPS, SSH and GitHub CLI (HTTPS tab goes first in UI)
Mentioned problem with credentials appears when repository is cloned via HTTPS. Solution here is to clone repository with SSH instead:
After that git should not ask you for credentials anymore.