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ADJTIMEX
!!!ADJTIMEX

----
!!NAME


adjtimex - tune kernel clock
!!SYNOPSIS

 __#include <sys/time>
 __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.
;[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

__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 SVr4.

!!SEE ALSO

settimeofday(2)
----

4 pages link to adjtimex(2):

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Last edited on Monday, October 28, 2002 8:45:20 pm by PerryLorier

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