vi /etc/ssh/sshd_config
#PermitRootLogin yes의 주석을 풀고 no 로 변경
+++++++++++++++++ 예 시(sshd_config) ++++++++++++++++++++++++++++++++
생략.............................
# Authentication:
#LoginGraceTime 2m
#PermitRootLogin yes
PermitRootLogin no
#StrictModes yes
#MaxAuthTries 6
생략.............................