Unable to connect to the server via FTP using root user.
The following lines occur in the connection establishment:
# Command: USER root
Response: 331 Password required for root
Command: PASS *********
Response: 530 Login incorrect.
Error: Critical error: Could not connect to server
The following records occur in /var/log/secure:
CONFIG_TEXT: CONSECURITY VIOLATION: Root login attempted
FTP connection as root is not allowed by default.
By default, the FTP connection as root is not allowed, since this is the security risk. The system user should be used to log in. For more information check proftpd documentation.