When debug mode is enabled (the -debug flag is passed) Packer pauses after executing each step. But when it comes to boot commands, it executes all of them without pausing. For debugging purpose it would be useful if Packer paused before each boot command in debug mode (or perhaps requiring an additional flag). This is useful to debug installations which require many steps (many boot commands) to complete. For example operating systems that don't offer an automatic/non-interactive installation option. It's fairly easy for the boot commands and the actual installation to get auto of sync and pausing before each boot command allows to manually verify that the installation is at the expected step.