Inspect system timers, verify clock sources and measure drift to troubleshoot missed or delayed jobs. 16.11.2025 | reading time: 3 min He wants to know whether jobs run late and why the clock seems to wander; start by checking the system clock, the hardware clock and systemd timers to find the culprit quickly. Measure clocks on a test VM On a test VM run the following commands to inspect time services and timers, then compare values to spot drift: ```bash timedatectl status hwclock --show systemctl list-timers --all --no-pager ``` Sample condensed output might look like this: ``` Local time: Mon 2025-11-17 11:02:00 UTC RTC time: Mon 2025-11-17 11:01:58 NTP synchronized: yes NEXT LEFT LAST PASSED Mon 2025-11-17 12:00:00 UTC 57min Mon 2025-11-17 10:00:00 UTC 1h 2min ago ``` Compare the RTC and Local time and watch the "LEFT" and "PASSED" columns for timers that miss or accumulate delay. Check accuracy and clock sources Drill deeper by checking the kernel clocksource and monotonic timers because systemd timers use CLOCK_MONOTONIC for intervals; verify `cat /sys/devices/system/clocksource/clocksource0/current_clocksource` and watch for changes under load, and remember that tickless kernels and CPU frequency scaling can shift perceived timing accuracy. Tune timer units and NTP interaction When a timer is slightly late, inspect the unit for accuracy and persistent settings: fields such as OnBootSec, OnUnitActiveSec and AccuracySec influence scheduling; also make sure NTP adjustments do not step the clock unexpectedly — prefer gradual slewing when precise intervals matter. Hands-on troubleshooting checklist If timers are flaky, do this: confirm NTP or chrony is healthy, compare `hwclock` to system time, list systemd timers and check journal entries for the unit with `journalctl -u your-timer.timer`, and isolate whether the issue is timer scheduling, CPU starvation or clocksource instability by running short targeted tests under load. Resources and further reading Explore systemd timer documentation for unit fields, the kernel docs on clock sources and POSIX timer semantics for CLOCK_MONOTONIC vs CLOCK_REALTIME, and practice reproducing timing issues in a controlled VM before touching production systems. Final thought Timers look small, but timing bugs can silently corrupt workflows; learn to measure clocks, read timer units and correlate logs so he can find the fault quickly and fix it cleanly — keep studying Linux and consider formalizing that knowledge with a certificate like CompTIA Linux+ or LPIC-1 and intensive exam preparation at bitsandbytes.academy. Join Bits & Bytes Academy First class LINUX exam preparation. utilities boot-process processes troubleshooting
