adjtime (3)
Leading comments
Copyright (c) 2006 by Michael Kerrisk <mtk.manpages@gmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this on...
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(): _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 |
CONFORMING TO
4.3BSD, System V.NOTES
The adjustment that adjtime() makes to the clock is carried out in such a manner that the clock is always monotonically increasing. Using adjtime() to adjust the time prevents the problems that can be caused for certain applications (e.g., make(1)) by abrupt positive or negative jumps in the system time.adjtime() is intended to be used to make small adjustments to the system time. Most systems impose a limit on the adjustment that can be specified in delta. In the glibc implementation, delta must be less than or equal to (INT_MAX / 1000000 - 2) and greater than or equal to (INT_MIN / 1000000 + 2) (respectively 2145 and -2145 seconds on i386).