adjtime - correct the time to allow synchronization of the system clock
struct timeval *delta;
struct timeval *olddelta;
Adjtime makes small adjustments to the system time, as returned by gettimeofday(2),
advancing or retarding it by the time specified by the timeval delta. If delta is nega-
tive, the clock is slowed down by incrementing it more slowly than normal until the cor-
rection is complete. If delta is positive, a larger increment than normal is used. The
skew used to perform the correction is generally a fraction of one percent. Thus, the
time is always a monotonically increasing function. A time correction from an earlier
call to adjtime may not be finished when adjtime is called again. If olddelta is non-
zero, then the structure pointed to will contain, upon return, the number of microseconds
still to be corrected from the earlier call.
This call may be used by time servers that synchronize the clocks of computers in a local
area network. Such time servers would slow down the clocks of some machines and speed up
the clocks of others to bring them to the average network time.
The call adjtime(2) is restricted to the super-user.
A return value of 0 indicates that the call succeeded. A return value of -1 indicates
that an error occurred, and in this case an error code is stored in the global variable
The following error codes may be set in errno:
[EFAULT] An argument points outside the process's allocated address space.
[EPERM] The process's effective user ID is not that of the super-user.
date(1), gettimeofday(2), timed(8), timedc(8),
TSP: The Time Synchronization Protocol for UNIX 4.3BSD, R. Gusella and S. Zatti
Adjtime(2) calls are executed immediately, not over a period of time, therefore, the old-
delta return values for an adjtime(2) call will always be zero.
4.3 Berkeley Distribution May 15, 1986 ADJTIME(2)