jammy (2) adjtime.2freebsd.gz

NAME

     adjtime — correct the time to allow synchronization of the system clock

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/time.h>

     int
     adjtime(const struct timeval *delta, struct timeval *olddelta);

DESCRIPTION

     The adjtime() system call 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 negative, the clock is
     slowed down by incrementing it more slowly than normal until the correction 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 not a
     null pointer, 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 adjtime() system call is restricted to the super-user.

RETURN VALUES

     The adjtime() function returns the value 0 if successful; otherwise the value -1 is returned and the global
     variable errno is set to indicate the error.

ERRORS

     The adjtime() system call will fail if:

     [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.

SEE ALSO

     date(1), gettimeofday(2), timed(8), timedc(8)

     R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX 4.3BSD.

HISTORY

     The adjtime() system call appeared in 4.3BSD.