I get it. Maybe something is wrong in my VM system so I can't git repo. I'll resolve it and try again. Thank you^-^
root@ubuntu-vm-1:~/stemcells# git clone g...@github.com:cloudfoundry/bosh-release.git
Cloning into 'bosh-release'...
The authenticity of host 'github.com (192.30.252.128)' can't be established.
RSA key fingerprint is 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'github.com,192.30.252.128' (RSA) to the list of known hosts.
Permission denied (publickey).
fatal: The remote end hung up unexpectedly