adjtime (3)
NAME
adjtime - correct the time to synchronize the system clockSYNOPSIS
#include <sys/time.h>
int adjtime(const struct timeval *delta, struct timeval *olddelta);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
adjtime():
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_BSD_SOURCE
DESCRIPTION
The adjtime() function gradually adjusts the system clock (as returned by gettimeofday(2)). The amount of time by which the clock is to be adjusted is specified in the structure pointed to by delta. This structure has the following form:
struct timeval { time_t tv_sec; /* seconds */ suseconds_t tv_usec; /* microseconds */
};
If the adjustment in delta is positive, then the system clock is speeded up by some small percentage (i.e., by adding a small amount of time to the clock value in each second) until the adjustment has been completed. If the adjustment in delta is negative, then the clock is slowed down in a similar fashion. If a clock adjustment from an earlier adjtime() call is already in progress at the time of a later adjtime() call, and delta is not NULL for the later call, then the earlier adjustment is stopped, but any already completed part of that adjustment is not undone. If olddelta is not NULL, then the buffer that it points to is used to return the amount of time remaining from any previous adjustment that has not yet been completed.
RETURN VALUE
On success, adjtime() returns 0. On failure, -1 is returned, and errno is set to indicate the error.ERRORS
- EINVAL
- The adjustment in delta is outside the permitted range.
- EPERM
- The caller does not have sufficient privilege to adjust the time. Under Linux, the CAP_SYS_TIME capability is required.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| adjtime () | Thread safety | MT-Safe |