The adjtimex System Call

Although clock drift ensures that all systems eventually move away from the correct time, changing the time abruptly is both an administrative nuisance and risky behavior. Imagine, for instance, programmers trying to build a large program and depending on filetime stamps to make sure that out-of-date object files are recompiled. A large change in the system's time could confuse the make program and lead to an incorrect build. Keeping the clocks tuned is also important when implementing a distributed filesystem on a network of computers. In this case, it is wise to adjust the clocks of the interconnected PCs so that the timestamp values associated with the inodes of the accessed files are coherent. Thus, systems are often configured to run a time synchronization protocol such as Network Time Protocol (NTP) on a regular basis to change the time gradually at each tick. This utility

This system call is present in several Unix variants, although it should not be used in programs intended to be portable. It receives as its parameter a pointer to a timex structure, updates kernel parameters from the values in the timex fields, and returns the same structure with current kernel values. Such kernel values are used by update_wall_time_one_tick( ) to slightly adjust the number of microseconds added to xtime.tv_usec at each tick.

Continue reading here: Requesting and Releasing Page Frames

Was this article helpful?