adjtime(2) System Calls Manual adjtime(2)
Name
adjtime - correct the time to allow synchronization of the system clock
Syntax
#include <sys/time.h>
adjtime(delta, olddelta)
struct timeval *delta;
struct timeval *olddelta;
Description
The system call changes the system time, as returned by moving it backward or forward by the number of microseconds corresponding to the
timeval delta.
The time is maintained by incrementing it with a machine-dependent tick every clock interrupt. If delta is negative, the clock is slowed
down by incrementing it in smaller ticks until the correction is made. If delta is positive, a larger tick is used. Thus, the time is
always a monotonically increasing function. A time correction from an earlier call to may not be finished when is called again. If old-
delta is nonzero, then the structure pointed to will contain, upon return, the number of microseconds still to be corrected from the ear-
lier call.
This call can be used in 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 call is restricted to the superuser.
Note
Time is incremented in 3906-microsecond (us) ticks on RISC and 10000 us ticks on VAX. When is called with a delta less than 1 second, time
is incremented according to the following table until the time is corrected:
-------------------------------------------
Default Fast Slow
System Increment Increment Increment
-------------------------------------------
RISC 3906 us 3921 us 3891 us
VAX 10000 us 10001 us 9999 us
-------------------------------------------
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.
Diagnostics
The following error codes may be set in errno:
[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)
adjtime(2)