1ADJTIME(3) Linux Programmer's Manual ADJTIME(3)
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6 adjtime - correct the time to synchronize the system clock
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9 int adjtime(const struct timeval *delta, struct timeval *olddelta);
10 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
12 adjtime(): _BSD_SOURCE
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16 The adjtime() function gradually adjusts the system clock (as returned
17 by gettimeofday(2)). The amount of time by which the clock is to be
18 adjusted is specified in the structure pointed to by delta. This
19 structure has the following form:
20 struct timeval {
22 time_t tv_sec; /* seconds */
23 suseconds_t tv_usec; /* microseconds */
24 };
25 If the adjustment in delta is positive, then the system clock is
27 speeded up by some small percentage (i.e., by adding a small amount of
28 time to the clock value in each second) until the adjustment has been
29 completed. If the adjustment in delta is negative, then the clock is
30 slowed down in a similar fashion.
31 If a clock adjustment from an earlier adjtime() call is already in
33 progress at the time of a later adjtime() call, and delta is not NULL
34 for the later call, then the earlier adjustment is stopped, but any
35 already completed part of that adjustment is not undone.
36 If olddelta is not NULL, then the buffer that it points to is used to
38 return the amount of time remaining from any previous adjustment that
39 has not yet been completed.
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42 On success, adjtime() returns 0. On failure, -1 is returned, and errno
43 is set to indicate the error.
44
46 EINVAL The adjustment in delta is outside the permitted range.
47 EPERM The caller does not have sufficient privilege to adjust the
49 time. Under Linux the CAP_SYS_TIME capability is required.
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52 4.3BSD, System V.
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55 The adjustment that adjtime() makes to the clock is carried out in such
56 a manner that the clock is always monotonically increasing. Using adj‐
57 time() to adjust the time prevents the problems that can be caused for
58 certain applications (e.g., make(1)) by abrupt positive or negative
59 jumps in the system time.
60 adjtime() is intended to be used to make small adjustments to the sys‐
62 tem time. Most systems impose a limit on the adjustment that can be
63 specified in delta. In the glibc implementation, delta must be less
64 than or equal to (INT_MAX / 1000000 - 2) and greater than or equal to
65 (INT_MIN / 1000000 + 2) (respectively 2145 and -2145 seconds on i386).
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68 A longstanding bug meant that if delta was specified as NULL, no valid
69 information about the outstanding clock adjustment was returned in old‐
70 delta. (In this circumstance, adjtime() should return the outstanding
71 clock adjustment, without changing it.) This bug is fixed on systems
72 with glibc 2.8 or later and Linux kernel 2.6.26 or later.
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75 adjtimex(2), gettimeofday(2), time(7)
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78 This page is part of release 3.25 of the Linux man-pages project. A
79 description of the project, and information about reporting bugs, can
80 be found at http://www.kernel.org/doc/man-pages/.
81Linux 2008-06-22 ADJTIME(3)