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.

Debian                                            June 4, 1993                                        ADJTIME(2)