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ADJTIME - reference manual online

Correct the time to synchronize the system clock.

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2015-03-02
ADJTIME(3)                          Linux Programmer's Manual                          ADJTIME(3)

NAME adjtime - correct the time to synchronize the system clock
SYNOPSIS #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 gettimeof‐ day(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 adjust‐ ment 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 sys‐ tems impose a limit on the adjustment that can be specified in delta. In the glibc imple‐ mentation, 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).
BUGS 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, adj‐ time() 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.
SEE ALSO adjtimex(2), gettimeofday(2), time(7)
COLOPHON This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.
Linux 2015-03-02 ADJTIME(3)
This manual Reference Other manuals
adjtime(3) referred by adjtimex(2) | clock_getres(2) | time(7)
refer to adjtimex(2) | attributes(7) | feature_test_macros(7) | gettimeofday(2) | make(1) | time(7)