Login In Oracle Database Service Cloud as root user

Cause :

Oracle doesn't allow direct access to root on cloud machines. sudo is the only option users have to access the root privileges.

Solution for the above issue:
1. change the below file
/etc/ssh/sshd_config
change
PermitRootLogin no
to
PermitRootLogin yes
change
AllowUsers opc oracle
to
AllowUsers opc oracle root
2. copy the authorization keys from oracle home/opc/.ssh folder to /root/.ssh/
cp /home/opc/.ssh/authorized_keys /root/.ssh/
OR  if there is a authorized_keys file already present in /root/.shh/ directory then append that file with the authorized_key present in /opc/.ssh/
3. service sshd restart
Try connecting to machine using the same private key as root user from putty.