Linux systems use ssh to login, you can use password and secret key landing. Using password every time you need to enter a password for authentication, you can log in to the verification by the environment.
Landing on the client secret key to generate a corresponding server side public and private keys, public keys for encryption and the private key for decryption. Then the public key to the server to be connected. When a client needs to connect the server, the server will use public key encryption to send user names and passwords to the client, the client using the corresponding private key to decrypt, verify that you can log in to the server through.
Sometimes necessary, we need to force use password authentication to login.
Forced password provided as follows:
config file in the directory client /root/.ssh/ additional line PreferredAuthentications password
echo PreferredAuthentications password >> /root/.ssh/config
config file may not exist, you can create and write files directly to the above-mentioned fields.
Restart sshd service: systemctl restart sshd
Again ssh remote login using a password that is mandatory landing approach.