To disable GSS API, first open/etc/ssh/sshd_config in your favorite editor
vi /etc/ssh/sshd_config
Then find the line that says GSSAPIAuthentication yes and change it to GSSAPIAuthentication no
sed -i 's/GSSAPIAuthentication yes/GSSAPIAuthentication no/g' etc/ssh/sshd_config
and save the file. Finally, restart the sshd service.
service sshd restart