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ADJTIMEX(2)			    Linux Programmer's Manual			      ADJTIMEX(2)

       adjtimex - tune kernel clock

       #include <sys/timex.h>

       int adjtimex(struct timex *buf);

       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

       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 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.

       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.


Linux 2.0				    1997-07-30				      ADJTIMEX(2)
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