adjtime
—
correct the time to allow synchronization of the
system clock
Standard C Library (libc, -lc)
#include
<sys/time.h>
int
adjtime
(
const
struct timeval *delta,
struct timeval
*olddelta);
The
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
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 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
adjtime
() system call is restricted to
the super-user.
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.
The
adjtime
() system call 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.
date(1),
gettimeofday(2),
timed(8),
timedc(8)
R. Gusella and
S. Zatti, TSP: The Time
Synchronization Protocol for UNIX 4.3BSD.
The
adjtime
() system call appeared in
4.3BSD.