settime

Settime is a general term used to describe the operation of assigning a new value to a clock or timestamp in computing systems. It can refer to an explicit programming interface or to administrative actions that change the time kept by a device. The concept covers both wall clock time (human-meaningful date and time) and internal clocks used for timing operations.

In Unix-like operating systems, several APIs allow setting the system clock. The settimeofday function and the clock_settime function provide ways to adjust wall clock time, typically for clocks such as CLOCK_REALTIME. Implementations usually require elevated privileges because changing the system time can affect scheduling, logging, and time-based security checks. Adjtime is another mechanism that gradually adjusts time to avoid abrupt jumps.

In Windows environments, time is set using APIs such as SetSystemTime, which updates the system’s UTC-based clock, and SetLocalTime for local time values. Both operations generally require administrator or equivalent privileges and appropriate safeguards to prevent tampering.

Time synchronization protocols play a central role in how settime is used in networks. Network Time Protocol (NTP) and Precision Time Protocol (PTP) allow devices to automatically adjust their clocks to a reference time source. Automatic synchronization reduces the need for manual changes and helps maintain consistent timestamps across systems, which is important for logging, security, and distributed computing. Manual changes to time can introduce inconsistencies, especially in distributed operations or forensic contexts.

Security and reliability considerations include protecting access to time-setting functions, validating time sources, and accounting for clock skew and leap seconds. Proper handling of time values and time zones is essential for accurate timestamps and orderly event sequencing.