$ git clone git@github.com:yourusername/xxx.git
Cloning into 'xxx'...
ssh: connect to host github.com port 22: Connection timed out
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.
Put the following text into ~/.ssh/config
Host github.com
Hostname ssh.github.com
Port 443
$ ssh -T git@github.com
Hi username! You've successfully authenticated, but GitHub does not provide shell access.