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ADJTIMEX
Section: Linux Programmer's Manual (2)
Updated: 2004-05-27
Index
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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
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.
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 3.05 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- SEE ALSO
-
- COLOPHON
-
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