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
       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.

       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.


       EFAULT buf does not point to writeable memory.

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

       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 sys­
              tem 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.