Issue
When trying to start Liferay, the starting process gets stuck at : 'Starting initial bundles'.
Environment
Liferay DXP 7.2 with a database connected
Resolution
Restarting the database server and the portal should solve the issue.
Checking the max number of clients on the DB side as well as the timeout is important to avoid such issue from happening again.
In that case, make sure that Liferay JDBC connection configuration has a lower timeout than the DB server.
If this does not solve the issue, you should open a support ticket and attach your thread dump.
Additional Information
The reason behind is that the DB is not responding because of 'too many clients'. It can occur when the portal was not shut down properly (e.g., kill -9) and the DB server still has the connections from the previously shut down JDBC connection pool. At the next startup, when Liferay loads the initial bundles, it makes a request against the DB to get the OSGi configuration from the Configuration_ table.