What to do if MariaDB's Navicat MySQL 8.0.x version reports a connection error?

If Navicat for MySQL 8.0.x reports a connection error with MariaDB, follow these steps to diagnose and resolve the issue:

Check Network Connectivity
Ensure the MariaDB server is reachable from your client machine. Use ping or telnet to verify the connection:
```
ping <MariaDB_server_IP>  
telnet <MariaDB_server_IP> 3306  
```
If the port is blocked, check firewall settings or security groups (e.g., Tencent Cloud Security Group rules).
Verify MariaDB Server Status
Confirm MariaDB is running on the server:
```
systemctl status mariadb  
```
If stopped, restart it:
```
systemctl start mariadb  
```
Check User Privileges
Ensure the MySQL user has the correct permissions to connect from the client IP. Log in to MariaDB locally and run:
```
SELECT host, user FROM mysql.user;  
GRANT ALL PRIVILEGES ON *.* TO 'username'@'client_IP' IDENTIFIED BY 'password';  
FLUSH PRIVILEGES;  
```
Replace username, client_IP, and password with your credentials.
Validate Connection Settings in Navicat
Double-check the connection details in Navicat:
- Hostname/IP address (e.g., 127.0.0.1 or remote server IP).
- Port (default is 3306).
- Username and password.
- Ensure "Use SSL" is unchecked unless required.
Check MariaDB Configuration
Verify bind-address in /etc/mysql/my.cnf or /etc/mysql/mariadb.conf.d/50-server.cnf:
```
bind-address = 0.0.0.0  # Allows remote connections  
```
Restart MariaDB after changes:
```
systemctl restart mariadb  
```
Enable Logging for Debugging
Check MariaDB error logs for details:
```
tail -f /var/log/mysql/error.log  
```
Tencent Cloud-Specific Recommendations
If using Tencent Cloud, ensure:
- The MariaDB instance is in the same VPC as your client or has proper peering.
- Security Group rules allow inbound traffic on port 3306 from your client IP.
- Use Tencent Cloud’s Database Connection Pooling or Private Network Access for enhanced security and performance.

Example: If connecting from a remote machine, ensure the Tencent Cloud Security Group allows 3306 from your IP, and the MariaDB user has % (any host) or your specific IP in privileges.