adjtimex - tune kernel clock
int adjtimex(struct timex *buf);
Linux uses David L. Mills' clock adjustment algorithm.
adjtimex reads and optionally sets adjustment parameters
for this algorithm.
adjtimex 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:
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 writeable memory.
EPERM buf.mode is non-zero and the user is not super-
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.
adjtimex is Linux specific and should not be used in pro
grams intended to be portable. There is a similar but
less general call adjtime in SVr4.