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NAME    [Toc]    [Back]

       adjtimex - tune kernel clock

SYNOPSIS    [Toc]    [Back]

       #include <sys/timex.h>

       int adjtimex(struct timex *buf);

DESCRIPTION    [Toc]    [Back]

       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

	      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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       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

SEE ALSO    [Toc]    [Back]


Linux 2.0			  1997-07-30			   ADJTIMEX(2)
[ Back ]
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