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ADJFREQ(2) System Calls Manual ADJFREQ(2)

adjfreq
correct the rate of the system clock

#include <sys/types.h>
#include <sys/time.h>
int
adjfreq(const int64_t *freq, int64_t *oldfreq);

adjfreq() adjusts the rate in which time progresses if freq is non-null. The unit of the rate of adjustment is nanoseconds per second, shifted left 32 bits to allow for fractional values.
If oldfreq is non-null, the current value is returned.
Only the superuser may adjust the frequency.

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

adjfreq() will fail if:
 
 
[]
Either of the arguments point outside the process's allocated address space.
 
 
[]
The freq argument is non-null and the process's effective user ID is not that of the superuser.

date(1), adjtime(2), gettimeofday(2), ntpd(8)

The adjfreq() function call first appeared in OpenBSD 4.0.
September 10, 2015 OpenBSD-current