linux man page for adjtime

ADJTIME(2)						     Linux Programmer's Manual							ADJTIME(2)

NAME
       adjtime - smoothly tune kernel clock

SYNOPSIS
       #include <sys/time.h>

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

DESCRIPTION
       This function speeds up or slows down the system clock in order to make a gradual adjustment.  This ensures that the calendar time reported
       by the system clock is always monotonically increasing, which might not happen if you simply set the clock.

       The delta argument specifies a relative adjustment to be made to the clock time.  If negative, the system clock is slowed down  fora  while
       until it has lost this much elapsed time.  If positive, the system clock is speeded up for a while.

       If  the	olddelta  argument is not a null pointer, the adjtime function returns information about any previous time adjustment that has not
       yet completed.

       This function is typically used to synchronize the clocks of computers in a local network.  You must be a privileged user to use it.

RETURN VALUE
       The adjtime function returns 0 on success and -1 on failure and sets the external variable errno accordingly.

ERRORS
       EPERM  The calling process does not have enough privileges to access the clock.

NOTE
       With a Linux kernel, you can use the adjtimex(2) function to permanently change the system clock speed.

CONFORMING TO
       This function is derived from 4.3 BSD and SVr4.

SEE ALSO
       adjtimex(2), settimeofday(2)

Linux 2.0							    2002-02-16								ADJTIME(2)