For my sins, I've worked on an old HP-UX system back in the Before-Times and that once required knowledge of vi to get it booting - no nano on that system. For

For my sins, I've worked on an old HP-UX system back in the Before-Times and that once required knowledge of vi to get it booting - no nano on that system. For more modern systems, you can end up in BusyBox and not have access to nano (I think you can specify that vi gets included in BusyBox).