Ntp

systemd-timesyncd is a minimal SNTP client for synchronizing the local system clock against configured time sources. It can help keep certificate checks and wall-clock timestamps meaningful, but it does not provide an unconditional accuracy guarantee. Whether the daemon can run, whether it receives acceptable samples, and whether the system reports synchronization are separate facts to establish. ...

A time daemon is useful only when its operating state supports the application’s time requirements. A running process can have no usable source, and a selected source can still be wrong or insufficiently measured. Treat time service health as an observable chain: source configuration, successful observations, selection, uncertainty, and permitted clock control. A green process indicator covers only the beginning. ...