ADJTIME(2) BSD System Calls Manual ADJTIME(2)NAMEadjtime — 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);
DESCRIPTIONAdjtime() 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 incre‐
menting 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 correc‐
tion from an earlier call to adjtime() may not be finished when adjtime()
is called again. If olddelta is non-nil, 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 com‐
puters 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 call adjtime() 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.
ERRORSAdjtime() 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 ALSOdate(1), gettimeofday(2), timed(8), timedc(8)
R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX
4.3BSD.
HISTORY
The adjtime() function call appeared in 4.3BSD.
BSD June 4, 1993 BSD
