You can view the log output of running instances from either the Log tab of the dashboard or the output of nova console-log. In some cases, the log output of a running Linux instance will be empty or only display a single character (for example, the ? character).
This occurs when the Compute service attempts to retrieve the log output of the instance via a serial console while the instance itself is not configured to send output to the console. To rectify this, append the following parameters to kernel arguments specified in the instance's boot loader:
console=tty0 console=ttyS0,115200n8
Upon rebooting, the instance will be configured to send output to the Compute service.
