ntpdrift
ntpdrift is a simple, plain-text file used by the Network Time Protocol daemon (ntpd) to store the estimated frequency error of the local clock. By persisting the drift value across restarts, ntpd can start with a better initial frequency correction and converge more quickly to accurate time.
Location and format: On most systems, the drift file is named ntp.drift or ntpdrift and is located
Update behavior: ntpd reads the drift on startup. As the daemon runs, it measures the clock's frequency
Administration and security: The drift file is normally owned by root and writable by the ntp process.