1. Check the error log for the MySQL 126 error:

$ tail -f /var/log/mysql/error.log

2. Check the MySQL configuration file for any misconfigurations:

$ cat /etc/mysql/my.cnf

3. Check the system variables for any misconfigurations:

$ mysql -u root -p
mysql> SHOW VARIABLES;

4. Check the system status for any misconfigurations:

mysql> SHOW STATUS;

5. Check the system processes for any misconfigurations:

mysql> SHOW PROCESSLIST;

6. Check the system tables for any misconfigurations:

mysql> SHOW TABLE STATUS;

7. Check the system privileges for any misconfigurations:

mysql> SHOW GRANTS;

8. Check the system logs for any misconfigurations:

mysql> SHOW LOGS;

9. Check the system users for any misconfigurations:

mysql> SELECT USER();

10. Use an automated database observability tool to monitor and fix the MySQL 126 in question. Automated database observability tools can provide real-time insights into the performance and health of your database, allowing you to quickly identify and fix any issues that may arise. These tools can also provide detailed metrics and logs that can help you diagnose and troubleshoot any MySQL 126 errors.