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.\" Copyright (c) 1995 Michael Chastain (mec@shell.portal.com), 15 April 1995.
.\"
.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
.\" 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, see
.\" <http://www.gnu.org/licenses/>.
.\" %%%LICENSE_END
.\"
.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1997-07-30 by Paul Slootman <paul@wurtel.demon.nl>
.\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" FIXME 2.6.26 added ADJ_TAI
.\" commit 153b5d054ac2d98ea0d86504884326b6777f683d
.\" FIXME 2.6.26 added ADJ_MICOR and ADJ_NANO
.\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
.\" Author: Roman Zippel <zippel@linux-m68k.org>
.\" FIXME 2.6.39 added ADJ_SETOFFSET
.\" commit 094aa1881fdc1b8889b442eb3511b31f3ec2b762
.\" Author: Richard Cochran <richardcochran@gmail.com>
.\"
.TH ADJTIMEX 2 2014-05-28 "Linux" "Linux Programmer's Manual"
.SH NAME
adjtimex \- tune kernel clock
.SH SYNOPSIS
.nf
.BR "#define _BSD_SOURCE" " /* See feature_test_macros(7) */"
.B #include <sys/timex.h>
.BI "int adjtimex(struct timex *" "buf" );
.fi
.SH DESCRIPTION
Linux uses David L. Mills' clock adjustment algorithm (see RFC\ 1305).
The system call
.BR adjtimex ()
reads and optionally sets adjustment parameters for this algorithm.
It takes a pointer to a
.I timex
structure, updates kernel parameters from field values,
and returns the same structure with current kernel values.
This structure is declared as follows:
.PP
.in +4n
.nf
struct timex {
int modes; /* mode selector */
long offset; /* time offset (usec) */
long freq; /* frequency offset (scaled ppm) */
.\" FIXME -- what is the scaling unit? 2^16 ?
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 */
};
.fi
.in
.PP
The
.I modes
field determines which parameters, if any, to set.
It may contain a
.RI bitwise- or
combination of zero or more of the following bits:
.PP
.in +4n
.nf
#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() */
.fi
.in
.PP
Ordinary users are restricted to a zero value for
.IR modes .
Only the superuser may set any parameters.
.br
.ne 12v
.SH RETURN VALUE
On success,
.BR adjtimex ()
returns the clock state:
.PP
.in +4n
.nf
#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 */
.fi
.in
.PP
On failure,
.BR adjtimex ()
returns \-1 and sets
.IR errno .
.SH ERRORS
.TP
.B EFAULT
.I buf
does not point to writable memory.
.TP
.B EINVAL
An attempt is made to set
.I buf.offset
to a value outside the range \-131071 to +131071,
or to set
.I buf.status
to a value other than those listed above,
or to set
.I buf.tick
to a value outside the range
.RB 900000/ HZ
to
.RB 1100000/ HZ ,
where
.B HZ
is the system timer interrupt frequency.
.TP
.B EPERM
.I buf.modes
is nonzero and the caller does not have sufficient privilege.
Under Linux the
.B CAP_SYS_TIME
capability is required.
.SH CONFORMING TO
.BR adjtimex ()
is Linux-specific and should not be used in programs
intended to be portable.
See
.BR adjtime (3)
for a more portable, but less flexible,
method of adjusting the system clock.
.SH SEE ALSO
.BR settimeofday (2),
.BR adjtime (3),
.BR capabilities (7),
.BR time (7),
.BR adjtimex (8)
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