NAME
adjtime —
correct the time to allow
synchronization of the system clock
LIBRARY
library “libc”
SYNOPSIS
#include
<sys/time.h>
int
adjtime(const
struct timeval *delta,
struct timeval
*olddelta);
DESCRIPTION
adjtime()
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 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 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.
If the calling user is not the super user, the
adjtime()
system call will fail, and the adjtime() function in
the standard C library will try to use the
clockctl(4) device if present, thus making it possible for non
privileged users to adjust the system time. If
clockctl(4) is not present or not accessible, then
adjtime() returns EPERM.
RETURN VALUES
A return value of 0 indicates that the call succeeded. A return value of -1 indicates that an error occurred, and in this case an error code is stored in the global variable errno.
ERRORS
adjtime() 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), clockctl(4), 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.