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Create SSH Keys with PuTTY on Windows

Download and install PuTTY on your computer.

After installing putty, run PuTTYgen from start menu

You may customize Parameter at the bottom. But generally default values are appropriate.

Now click on Generate and move the mouse on blank area to complete key generation.

Save private key in save place. Noted that you may or may not use Key passphrase.

Close PuTTYgen tools.

Connect to server with Private Key

Open PuTTY

Put hostname or IP in session.

Go to Connection > SSH > Auth and browse private key.

Now you will be prompted Login as

 

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How to restrict direct root access | Linux | CentOS

We can do it just in two steps.

Step One:

At first we will create new root user as follows (for example, newroot)

  1. Login as root using SSH.
  2. Create new user e.g., newroot and add user to wheel group 
    useradd -G wheel newroot
  3. Set password for newroot 
    passwd newroot
  4. You will get option to enter password. Use letter and number only.
    Save the newroot and password somewhere of you edge.
  5. Su to newroot 
    su - newroot
  6. Test sudo permission (permission should be root) 
    sudo whoami
  7. Enter password of newroot and it will show result “root”.
  8. Open sshd config file and check whether it has the “newroot” in AllowUsers. If not, add the user manually. (usually at the end). 
    vi /etc/ssh/sshd_config

    [Permission Denied!] Quit :q

    AllowUsers newroot
  9. Restart sshd.service 
    sudo systemctl restart sshd.service

Step Two:

Now we are going to disable the root user. Before doing this, you have to logout from “root” and then login with “newroot”.

You can only disable the  “root”, if you can successfully login with “newroot”.

  1. After successfully login with “newroot”, su to “root” using root password. 
    su - root
  2. Then open sshd_config. 
    vi /etc/ssh/sshd_config
  3. Search and change permitRootLogin “yes” to “no” as follows. 
    permitRootLogin no
  4. Restart sshd.service to implement the change 
    sudo systemctl restart sshd.service
  5. Now logout from “newroot” and try to login “root”
  6. Login with root now not allowed. Access Deny.
  7. So login with “newroot” and then su to root with root password 
    su - root