• 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 to where HZ is the system timer interrupt frequency.

  EPERM

  buf.mode is non-zero 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 3.19 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/.

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