Measure the hardware clock, see how it drifts, and learn how to correct or compensate for it. 09.02.2026 | reading time: 2 min The hardware real time clock can drift away from the system clock; that causes timestamps to disagree after reboots or when the network is unavailable, so learn to measure and interpret that drift. Measure drift hands-on ```bash # Sync system time into the RTC and record initial readings $ sudo hwclock --systohc $ date --iso-8601=seconds 2026-02-08T11:00:00+00:00 $ sudo hwclock --show 2026-02-08 10:59:59.880544+00:00 # After two hours, recheck both clocks $ date --iso-8601=seconds 2026-02-08T13:00:00+00:00 $ sudo hwclock --show 2026-02-08 12:59:58.760544+00:00 # Interpretation: RTC lost ~1.24 seconds in 2 hours (~0.62 s/hour), a concrete drift you can quantify and log for trend analysis ``` Options that change behavior Use `--show` to read the RTC and `--systohc` or `--hctosys` to copy time between system and hardware clocks, use `--utc` or `--localtime` to match how the RTC is interpreted, and use `--adjust` together with the `/etc/adjtime` file to apply recorded drift corrections automatically. When to rely on network time An NTP client such as chrony or systemd-timesyncd disciplines the system clock continuously and is usually preferable for production systems; keep the system clock synced and update the RTC at shutdown or periodically, because hwclock does not continuously correct drift on its own. Practical tips for admins Measure drift by logging paired `date` and `hwclock --show` readings over hours or days, compute seconds per day to decide whether to compensate via adjtime or replace the RTC battery or device; record ambient conditions because temperature often affects crystal frequency. Next moves for learning Inspecting hwclock drift teaches a useful diagnostic workflow: measure, quantify, decide on software correction or hardware replacement; to deepen skills consider formal study toward CompTIA Linux+ or LPIC-1 and try intensive exam prep at bitsandbytes.academy. Join Bits & Bytes Academy First class LINUX exam preparation. utilities boot-process troubleshooting infrastructure
