adjtimex - tune kernel clock


SYNOPSIS

       #include <sys/timex.h>

       int adjtimex(struct timex *buf);


DESCRIPTION

       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 fol­
       lows:

              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.


ERRORS

       EFAULT buf does not point to writable 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 sys­
              tem timer interrupt frequency.


CONFORMING TO

       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.


SEE ALSO

       settimeofday(2)


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