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25 .TH ADJTIME 3 2014-05-28 "Linux" "Linux Programmer's Manual"
27 adjtime \- correct the time to synchronize the system clock
30 .B #include <sys/time.h>
32 .BI "int adjtime(const struct timeval *" delta ", struct timeval *" olddelta );
36 Feature Test Macro Requirements for glibc (see
37 .BR feature_test_macros (7)):
45 function gradually adjusts the system clock (as returned by
46 .BR gettimeofday (2)).
47 The amount of time by which the clock is to be adjusted is specified
48 in the structure pointed to by
50 This structure has the following form:
55 time_t tv_sec; /* seconds */
56 suseconds_t tv_usec; /* microseconds */
63 is positive, then the system clock is speeded up by some
64 small percentage (i.e., by adding a small
65 amount of time to the clock value in each second) until the adjustment
69 is negative, then the clock is slowed down in a similar fashion.
71 If a clock adjustment from an earlier
73 call is already in progress
74 at the time of a later
78 is not NULL for the later call, then the earlier adjustment is stopped,
79 but any already completed part of that adjustment is not undone.
83 is not NULL, then the buffer that it points to is used to return
84 the amount of time remaining from any previous adjustment that
85 has not yet been completed.
90 On failure, \-1 is returned, and
92 is set to indicate the error.
98 is outside the permitted range.
101 The caller does not have sufficient privilege to adjust the time.
104 capability is required.
106 .SS Multithreading (see pthreads(7))
109 function is thread-safe.
115 makes to the clock is carried out in such a manner that the clock
116 is always monotonically increasing.
119 to adjust the time prevents the problems that can be caused for certain
122 by abrupt positive or negative jumps in the system time.
125 is intended to be used to make small adjustments to the system time.
126 Most systems impose a limit on the adjustment that can be specified in
128 In the glibc implementation,
130 must be less than or equal to (INT_MAX / 1000000 \- 2)
131 and greater than or equal to (INT_MIN / 1000000 + 2)
132 (respectively 2145 and \-2145 seconds on i386).
135 .\" http://sourceware.org/bugzilla/show_bug?id=2449
136 .\" http://bugzilla.kernel.org/show_bug.cgi?id=6761
139 was specified as NULL,
140 no valid information about the outstanding clock adjustment was returned in
142 (In this circumstance,
144 should return the outstanding clock adjustment, without changing it.)
146 .\" Thanks to the new adjtimex() ADJ_OFFSET_SS_READ flag
147 on systems with glibc 2.8 or later and
148 Linux kernel 2.6.26 or later.
151 .BR gettimeofday (2),