Year 2038 Problem
en.wikipedia.org
en.wikipedia.org
I've got embedded Linux systems still on the 3.x kernel that have a good chance of still being in use in 2038. We've been backporting patches where and when we can.
[1] https://lore.kernel.org/lkml/CAK8P3a2iZyA1VSFqvcEc9o59F76Ggz...