systemd-time-wait-sync.service, systemd-time-wait-sync - Wait until kernel time is synchronized
systemd-time-wait-sync is a system service that delays the start of units that are ordered after time-sync.target (see systemd.special(7) for details) until the system time has been synchronized with an accurate remote reference time source by systemd-timesyncd.service.
systemd-timesyncd.service notifies systemd-time-wait-sync about successful synchronization. systemd-time-wait-sync also tries to detect when the kernel marks the system clock as synchronized, but this detection is not reliable and is intended only as a fallback for compatibility with alternative NTP services that can be used to synchronize time (e.g., ntpd, chronyd).
The presence of this file indicates to this service that the system clock has been synchronized.