adjtimex()函數 Unix/Linux

名稱

adjtimex - 調內核時鐘

內容簡介

#include <sys/timex.h>
int adjtimex(struct timex *buf);

描述

Linux使用大衛L. Mills的時鐘調整算法（參見RFC1305）。 adjtimex()係統調用讀取和任選設置該算法的調整參數。這需要一個指針的TIMEX結構，更新內核參數字段值，並返回相同的結構與當前的內核值。這種結構的聲明如下：

struct timex {
    int modes;           /* mode selector */
    long offset;         /* time offset (usec) */
    long freq;           /* frequency offset (scaled ppm) */
    long maxerror;       /* maximum error (usec) */
    long esterror;       /* estimated error (usec) */
    int status;          /* clock command/status */
    long constant;       /* pll time constant */
    long precision;      /* clock precision (usec) (read only) */
    long tolerance;      /* clock frequency tolerance (ppm)
                            (read only) */
    struct timeval time; /* current time (read only) */
    long tick;           /* usecs between clock ticks */
};

“modes ”字段確定的參數，如果有的話就設置。它可能包含一個按位或組合的零個或多個以下bits：

#define ADJ_OFFSET            0x0001 /* time offset */
#define ADJ_FREQUENCY         0x0002 /* frequency offset */
#define ADJ_MAXERROR          0x0004 /* maximum time error */
#define ADJ_ESTERROR          0x0008 /* estimated time error */
#define ADJ_STATUS            0x0010 /* clock status */
#define ADJ_TIMECONST         0x0020 /* pll time constant */
#define ADJ_TICK              0x4000 /* tick value */
#define ADJ_OFFSET_SINGLESHOT 0x8001 /* old-fashioned adjtime() */

普通用戶限製到零值模式mode。隻有超級用戶可以設置任何參數。

返回值

成功，adjtimex() 返回時鐘狀態：

#define TIME_OK   0 /* clock synchronized */
#define TIME_INS  1 /* insert leap second */
#define TIME_DEL  2 /* delete leap second */
#define TIME_OOP  3 /* leap second in progress */
#define TIME_WAIT 4 /* leap second has occurred */
#define TIME_BAD  5 /* clock not synchronized */

如果失敗，adjtimex（）返回-1，並設置errno。

錯誤

標簽	描述
EFAULT	buf does not point to writable memory.
EINVAL	An attempt is made to setbuf.offset to a value outside the range -131071 to +131071,or to set buf.status to a value other than those listed above,or to set buf.tick to a value outside the range 900000/HZ to 1100000/HZ, where HZ is the system timer interrupt frequency.
EPERM	buf.mode is non-zero and the caller does not have sufficient privilege.Under Linux the CAP_SYS_TIME capability is required.

遵循於

adjtimex() 是Linux特有的，並且不應該被用在程序準備移植. 查看adjtime（3）用於調整係統時鐘的方法，更輕便，但彈性較差。

另請參閱

settimeofday (2)