Este é o PuTTY tentando vários métodos de autenticação (por exemplo, GSSAPI) e o CentOS respondendo 'Não, obrigado'.
Para se livrar do erro, você deve desativar os métodos de autenticação extras do PuTTY ou configurá-los no sshd do CentOS.
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Uma pesquisa no Google confirmou que isso é um problema entre o PuTTY e o CentOS:
link
For the “Access denied” problem.
Most of the time this is caused by the new GSSAPI option in Putty 0.61. Go to Connection: SSH: Auth: GSSAPI an deactivate “Attempt GSSAPI authentication”
If that doesn’t help go to Putty log file by CTRL+Click on your Putty session and open up the normaly hidden menue entry “Event log”. There you should see what caused the access error.
Yes, that was it. Turning off the GSSAPI authentication eliminated the “Access denied” error message for me as well. I still think that I should update the OpenSSH software used by CentOS 5.6. It’s better to be safe than sorry. ;)