From the documentation at https://docs.spring.io/spring-boot/reference/features/logging.html#features.logging.console-output :

you can also specify debug=true in your application.properties.

When the debug mode is enabled, a selection of core loggers (embedded container, Hibernate, and Spring Boot) are configured to output more information.

When you set debug=true a bunch of "core" loggers used under the hood by spring boot will be set to debug: web container (like a tomcat), spring boot itself, hibernate.

It won't affect the loggers of your application though - they'll still be at INFO severity level.

However, if you set something like logging.level.root=debug probably all the loggers will be set to DEBUG, so yes, technically there is a difference.

From the spring boot documentation:

When the debug mode is enabled, a selection of core loggers (embedded container, Hibernate, and Spring Boot) are configured to output more information. Enabling the debug mode does not configure your application to log all messages with DEBUG level.

Adding debug=true to the application.properties or debug: true in the application.yml, file should help. You'll get more detailed logging.

Generally, if you want to see more fine-grained log messages from all members of a given package, you can set that by adding a line such as:

logging.level.<package_name>=<LOGGING_LEVEL>

for example:

logging.level.org.springframework.context=DEBUG

These log messages may be helpful in finding the core of the problem (in this case why a given exception was thrown).