When trying to SSH into GitHub.com on a Linux computer, you may see the following message in your terminal:
$ ssh -vT git@github.com
> ...
> Agent admitted failure to sign using the key.
> debug1: No more authentication methods to try.
> Permission denied (publickey).
For more details, see this issue report on Canonical Launchpad.
Resolution
You should be able to fix this error by loading your keys into your SSH agent with ssh-add:
# start the ssh-agent in the background
$ eval "$(ssh-agent -s)"
> Agent pid 59566
$ ssh-add
> Enter passphrase for /home/YOU/.ssh/id_rsa: [tippy tap]
> Identity added: /home/YOU/.ssh/id_rsa (/home/YOU/.ssh/id_rsa)
If your key does not have the default filename (/.ssh/id_rsa), you'll have to pass that path to ssh-add:
# start the ssh-agent in the background
$ eval "$(ssh-agent -s)"
> Agent pid 59566
$ ssh-add ~/.ssh/my_other_key
> Enter passphrase for /home/YOU/.ssh/my_other_key: [tappity tap tap]
> Identity added: /home/YOU/.ssh/my_other_key (/home/YOU/.ssh/my_other_key)