ADJTIMEX (2)

SYNOPSIS

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

DESCRIPTION

Linux uses David L. Mills' clock adjustment algorithm. adjtimex reads and optionally sets adjustment parameters for this algorithm.

adjtimex 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. 12v

RETURN VALUE

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 .

ERRORS

EFAULT

buf does not point to writeable memory.

EPERM

buf.mode is non-zero and the user is not super-user.

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.

CONFORMING TO

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.

SEE ALSO

settimeofday(2) man2/unimplemented 2