What does "SMP PREEMPT RT" mean in `uname -a`?

Question

As per the subject, here is the output of uname -a:

Linux 4.19.82 #1 SMP PREEMPT RT Mon Mar 2 17:33:16 PST 2020 x86_64 x86_64 x86_64 GNU/Linux

There is no related information in man uname indeed.

Answer 1

“SMP” means that the kernel was built with support for SMP (symmetric multi-processing).

“PREEMPT” means that the kernel was built as a preemptible kernel.

“RT”, on version 4.19, means that the kernel was built as a fully preemptible (real-time) kernel, using the Preempt RT patches.

The string you see in uname -a’s output is constructed by scripts/mkcompile_h based on the kernel’s build configuration options.