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 in the ntp data directory, often /var/lib/ntp or /var/lib/ntp/. The file contains a single decimal number representing the clock's drift, i.e., the rate at which the local clock advances compared to true time. In practice this is equivalent to the frequency offset, commonly described in parts per million (ppm).

Update behavior: ntpd reads the drift on startup. As the daemon runs, it measures the clock's frequency error and periodically writes the updated value back to the drift file. The drift file may also be updated on normal shutdown. If the file is missing or unreadable, ntpd uses a default drift, which may slow convergence.

Administration and security: The drift file is normally owned by root and writable by the ntp process. Permissions should prevent tampering. Do not edit the file manually; let ntpd manage it. If the file becomes corrupted, you can remove it and restart ntpd to create a new drift value.

See also: ntpd, NTP protocol, drift, time synchronization.