Are you sure your software is running? What about in the next few microseconds? Let’s walk through how to answer this question, and write latency-critical software on Linux. You’ll get a headstart from the hardware to userspace, learning about BIOS quirks, kernel settings, paging, tools, application design, and common pitfalls. We’ll squeeze determinism out of PREEMPT_RT Linux, reduce the jitter in our cycle-times and networking from milliseconds to microseconds, and show off some real hardware demos from the industrial automation field.