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adjtime.2freebsd

BSD mandoc

NAME

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

LIBRARY

Lb libc

SYNOPSIS

In sys/time.h Ft int Fn adjtime const struct timeval *delta struct timeval *olddelta

DESCRIPTION

The Fn 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 Fa delta . If Fa delta is negative, the clock is slowed down by incrementing it more slowly than normal until the correction is complete. If Fa 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 Fn adjtime may not be finished when Fn adjtime is called again. If Fa 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 Fn adjtime system call is restricted to the super-user.

RETURN VALUES

Rv -std adjtime

ERRORS

The Fn adjtime system call will fail if:

Bq Er EFAULT

An argument points outside the process's allocated address space.

Bq Er EPERM

The process's effective user ID is not that of the super-user.

SEE ALSO

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

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

HISTORY

The Fn adjtime system call appeared in BSD 4.3