adjtimex man page on ElementaryOS

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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 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

	   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 supe‐
       ruser 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.

       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 system 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.

       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.

       settimeofday(2), adjtime(3), capabilities(7), time(7), adjtimex(8)

       This  page  is  part of release 3.54 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux				  2013-08-07			   ADJTIMEX(2)

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