You can view the log output of a running instance by clicking the Log tab for that instance in the Dashboard. If the log output of a running Linux instance is empty or only displaying a single character, such as "?", the instance may not be configured to send output to the console.
To correct this, append the following parameters to kernel arguments specified in the instance's boot loader:
After you reboot the instance, it will be configured to send output to the Compute service.
NOTE: Amazon Machine Images (AMI) cannot accept these kernel arguments.