You may encounter the following error when you try to access Git Server via SSH on Linux:

Example:

$ ssh -vT git@github.com
...
# Agent admitted failure to sign using the key.
# debug1: No more authentication methods to try.
# Permission denied (publickey).

You should be able to fix this error by simply loading your keys into your SSH agent with ssh-add:

$ ssh-add

info on github: Error: Agent admitted failure to sign · GitHub Help