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Manuál Linux
[Linux manuál]

adjtimex: naladit hodiny jádra

Originální popis anglicky: adjtimex - tune kernel clock

Návod, kniha: Linux Programmer's Manual

STRUČNĚ

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

POPIS / INSTRUKCE

Linux uses David L. Mills' clock adjustment algorithm (see RFC 1305). The system call adjtimex reads and optionally sets adjustment parameters for this algorithm. It takes a pointer to a timex structure, updates kernel parameters from field values, and returns the same structure with current kernel values. This structure is declared as follows:
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 */
};
The modes field determines which parameters, if any, to set. It may contain a bitwise-or combination of zero or more of the following 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 */
Ordinary users are restricted to a zero value for mode. Only the superuser may set any parameters.
 

NÁVRATOVÁ HODNOTA

On success, adjtimex returns the clock state:
#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 */
On failure, adjtimex returns -1 and sets errno.

CHYBY / ERRORY

EFAULT
buf does not point to writable memory.
EINVAL
An attempt is made to set buf.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.

ODPOVÍDAJÍCÍ

adjtimex is Linux specific and should not be used in programs intended to be portable. There is a similar but less general call adjtime in SVr4.

SOUVISEJÍCÍ

settimeofday(2), capabilities(7)
2004-05-27 Linux 2.6.6
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