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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 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
       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.

       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.

       EPERM  buf.mode is nonzero and the caller does not have sufficient privilege.  Under Linux
	      the CAP_SYS_TIME capability is required.

CONFORMING TO
       adjtimex() is Linux-specific and should not be used in programs intended to  be	portable.
       See  adjtime(3)	for  a	more  portable, but less flexible, method of adjusting the system
       clock.

SEE ALSO
       settimeofday(2), adjtime(3), capabilities(7), time(7)

COLOPHON
       This page is part of release 3.53 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at
       http://www.kernel.org/doc/man-pages/.

Linux					    2004-05-27				      ADJTIMEX(2)
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