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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 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.

       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.sta-
              tus 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  non-zero  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)

       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at

Linux                             2004-05-27                       ADJTIMEX(2)