adjtimex

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



NAME
       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  parame-
       ters  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 parameters.

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 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 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)



Linux 2.0			  1997-07-30			  ADJTIMEX(2)