NAME
adjtime —
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);
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.