Debian Bookworm + Chrony in a Dual-Boot Setup: Why Windows and Linux Disagree on Time & Solution

The RTC is the motherboard clock that keeps time even when the machine is powered off. On boot, the OS reads that clock and decides how to interpret it. The conflict: Linux usually treats the RTC as UTC Windows usually treats the RTC as local time [1] Boot Linux | v Linux writes RTC = UTC | | Example: | Real local time = 15:00 | Timezone = UTC+2 | RTC stored = 13:00 (UTC) v [2] Reboot into Windows | v Windows reads same RTC value as LOCAL TIME | | Reads RTC 13:00 | Interprets it as local time v [3] Windows shows wrong clock | | Displayed time = 13:00 | Expected time = 15:00 | Error = -2 hours v (Not tested yet, but intuitively expected - the next steps) [4] Windows may write RTC back as LOCAL TIME | | RTC becomes 15:00 (but stored as localtime) v [5] Reboot back into Linux | v Linux reads RTC again as UTC | | Reads RTC 15:00 | Interprets it as UTC v [6] Linux shows wrong clock too | | 15:00 UTC = 17:00 local time (UTC+2) | Linux clock is now wrong v Result: Linux and Windows keep reint