Linux System Clock Explained: NTP, Drift and Monotonic Time
OSTechNix, Friday, October 23rd, 2026
Why Linux clocks drift and jump, how NTP keeps them honest, and why elapsed time needs a monotonic clock rather than wall-clock time.
Your computer's clock can drift, jump backward and disagree with other servers, and this guide explains why.
Linux offers CLOCK_REALTIME for wall-clock time and CLOCK_MONOTONIC for measuring elapsed time, since the wall clock can be stepped during corrections; the lesson is to use wall time for when something happened and monotonic time for how long it took.
It explains how NTP synchronizes clocks despite network delays and faulty sources, how to inspect status with timedatectl, and why scheduling something for 9 AM tomorrow is harder than waiting 86,400 seconds because of time zones and daylight saving.