On a Debian-based Linux system, such as Ubuntu, the default location of the MySQL error log file is /var/log/mysql/error.log. This file contains information about errors and other messages that are generated by the MySQL server.
You can view the MySQL error log by using the tail command to print the last few lines of the file, like this:
tail -f /var/log/mysql/error.log
This will show the most recent entries in the error log as they are added. You can also use the less command to view the entire error log, like this:
less /var/log/mysql/error.log
Keep in mind that the MySQL error log may contain sensitive information, such as passwords and SQL queries, so you should be careful about who has access to it.
If the MySQL error log file is not being created or is not located in the default location, you can check the my.cnf configuration file for the log_error option. This option specifies the location of the error log file. For example:
log_error = /var/log/mysql/error.log