adjtimex - tune kernel clock


     #include <sys/timex.h>

     int adjtimex(struct timex *buf));


     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  ker-
     nel  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.


     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.


          buf does not point to writeable memory.

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

          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.


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