Recently, my desktop hard disk crashed. So I reinstalled Linux and created a new set of private RSA keys for authentication. However, two of my remote UNIX servers still uses old DSA keys. I do not remember root password for those servers. I do have backup of private and public DSA keys and currently stored in /backup/home/user/.ssh/id_dsa and /backup/home/user/.ssh/id_dsa.pub. How do I force my ssh clients to use identity file /backup/home/user/.ssh/id_dsa to get back to my remote UNIX servers?
Many users are using ssh to log into a remote machine and append the indicated identity file to machine’s ~/.ssh/authorized_keys file. I recently moved one of my server, and I would like to revoke openssh keys and disable user access under Linux operating systems. How do I revoke OpenSSH keys under Unix or Linux operating systems?