ADJTIME(2)              COMMAND REFERENCE              ADJTIME(2)



NAME
     adjtime - correct the time to allow synchronization of the
     system clock

SYNOPSIS
     #include <sys/time.h>

     adjtime(delta, mode)
     struct timeval *delta;
     int mode;

DESCRIPTION
     The program adjtime changes the system time, as returned by
     gettimeofday(2), in the way specified by the argument mode.
     If mode is T_ADJ then adjtime moves the time back or forward
     by a number of milliseconds corresponding to the timeval
     delta while keeping the monotonicity of the function.  If
     mode is T_SET then delta milliseconds are added algebraicly
     to the time.

     This call can be used in timeservers that synchronize the
     clocks of computers in a network to keep an accurate network
     time.

     Only the superuser can call adjtime.  The time is normally
     incremented by a 20ms tick.  If T_ADJ is passed and delta is
     negative, the clock is incremented with a smaller tick for
     the time necessary to correct the error.  When delta is
     positive a larger tick is used.  This way, the clock is
     always a monotonic function.  With respect to this, adjtime
     with mode set to T_SET, should be used carefully and only at
     boot time before any users can log on.

     The T_SET mode has been introduced to make, at the process
     level, the operation of adding a value to the time an atomic
     one.

DIAGNOSTICS
     The program adjtime may set the following errors in errno:

     [EINVAL]
         mode is not valid.

     [EFAULT]
         An argument references invalid memory.

     [EPERM]
         The caller is not the superuser.

RETURN VALUE
     Upon successful completion, a value of 0 is returned.
     Otherwise, a value of -1 is returned and errno is set to



Printed 4/6/89                                                  1

ADJTIME(2)              COMMAND REFERENCE              ADJTIME(2)



     indicate the error.

SEE ALSO
     gettimeofday(2)



















































Printed 4/6/89                                                  2

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