Instroduce

When you launch a EC2 instance, the default:

• You have to use .pem(chmod 400 before use) for ssh login.
• You will only centos(or ec2-user) account for login(user permission)

And ofcourse you have only user permission.

STEP by STEP

1. Login to EC2 by default:

   $ chmod 400 my-key-pair.pem
   $ ssh -i my-key-pair.pem centos@{public ip}
   

2. Switch permission from user to root:

   $ sudo su

   Then you are able to change root password and do any root things.

   
   

3. Modify ssh to allow root login:

   # vi /etc/ssh/sshd_config

   Chenge:

   PermitRootLogin yes

   Save and Exit.
   
   

4. Modify ssh allow password login:

   # vi /etc/ssh/sshd_config

   Change:

   PasswordAuthentication yes

   Save and Exit.
   
   

5. Modify allow use .pem file for root login:

   vi /root/.ssh/authorized_keys

   Remove below section:

   command="echo 'Please login as the ec2-user user rather than root user.';echo;sleep 10"

   Save and Exit.
   
   

6. Restart sshd:

   # service sshd restart

You are now get root permission and able to login by password and .pem file.