adjtimex()函数 Unix/Linux

名称

adjtimex - 调内核时钟

内容简介

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

描述

Linux使用大卫L. Mills的时钟调整算法（参见RFC1305）。 adjtimex()系统调用读取和任选设置该算法的调整参数。这需要一个指针的TIMEX结构，更新内核参数字段值，并返回相同的结构与当前的内核值。这种结构的声明如下：

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 ”字段确定的参数，如果有的话就设置。它可能包含一个按位或组合的零个或多个以下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() */

普通用户限制到零值模式mode。只有超级用户可以设置任何参数。

返回值

成功，adjtimex() 返回时钟状态：

#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 */

如果失败，adjtimex（）返回-1，并设置errno。

错误

标签	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.

遵循于

adjtimex() 是Linux特有的，并且不应该被用在程序准备移植. 查看adjtime（3）用于调整系统时钟的方法，更轻便，但弹性较差。

另请参阅

settimeofday (2)