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.
buf does not
point to writable memory.
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.
buf.mode
is nonzero 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.
This page is part of release 2.79 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/.
|
Copyright (c) 1995 Michael Chastain (mecshell.portal.com), 15 April 1995. This is free documentation; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU General Public License's references to "object code" and "executables" are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this manual; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA. Modified 1997-01-31 by Eric S. Raymond <esrthyrsus.com> Modified 1997-07-30 by Paul Slootman <paulwurtel.demon.nl> Modified 2004-05-27 by Michael Kerrisk <mtk.manpagesgmail.com> |