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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | NOTES | BUGS | SEE ALSO | COLOPHON |
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adjtime(3) Library Functions Manual adjtime(3)
adjtime - correct the time to synchronize the system clock
Standard C library (libc, -lc)
#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
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.
On success, adjtime() returns 0. On failure, -1 is returned, and
errno is set to indicate the error.
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.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ adjtime() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
None.
4.3BSD, System V.
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
could 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).
A longstanding bug meant that if delta was specified as NULL, no
valid information about the outstanding clock adjustment was
returned in olddelta. (In this circumstance, adjtime() should
return the outstanding clock adjustment, without changing it.)
This bug is fixed on systems with glibc 2.8 or later and Linux
kernel 2.6.26 or later.
adjtimex(2), gettimeofday(2), time(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 adjtime(3)
Pages that refer to this page: adjtimex(2), clock_getres(2), timeval(3type), time(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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