What are the reasons that cause the time settings in Linux to become invalid after a restart?

1. Insufficient power in the BIOS/CMOS battery: The BIOS/CMOS battery is used to store system time and other BIOS settings. If the battery power is low, time settings may be lost when the system restarts.
2. The NTP service is not started or configured incorrectly: NTP (Network Time Protocol) is used to synchronize system time. If the NTP service is not properly started or configured incorrectly, the system may not automatically synchronize time after restart.
3. Hardware malfunction, such as a motherboard failure, could result in the system time being reset to its default value.
4. Software misconfiguration: Some software may reset the system time to its default value. For example, scheduled tasks or scripts may reset the time when the system restarts.
5. Malware or viruses: Some malicious software or viruses may change system time or reset time settings.
6. Network issue: If a system relies on network time synchronization (such as NTP), problems with the network connection could result in the failure of time synchronization.
7. Operating system error: Errors or issues within the operating system itself may cause the time settings to be lost after a reboot.

It should be noted that these possible reasons apply not just to Linux systems, but also to other operating systems.