The operating system for a given virtual machine can be located by browsing to the system disk which contains the operating system. This will generally only be visible should you let Katapult auto-configure your operating system where you do not otherwise provide the root password as part of the setup wizard.
The root password can be found under the the Installation details section.
Consider changing your root password!
It is strongly recommended that you change the default root password within the operating system itself to prevent unauthorised access.