mirror of https://github.com/mkerrisk/man-pages
155 lines
4.5 KiB
Groff
155 lines
4.5 KiB
Groff
.\" Copyright (c) 1995 Michael Chastain (mec@shell.portal.com), 15 April 1995.
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.\"
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.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, see
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.\" <http://www.gnu.org/licenses/>.
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.\" %%%LICENSE_END
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.\"
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.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 1997-07-30 by Paul Slootman <paul@wurtel.demon.nl>
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.\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" FIXME 2.6.29 added ADJ_SETOFFSET
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.\"
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.TH ADJTIMEX 2 2004-05-27 "Linux" "Linux Programmer's Manual"
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.SH NAME
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adjtimex \- tune kernel clock
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.SH SYNOPSIS
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.B #include <sys/timex.h>
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.sp
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.BI "int adjtimex(struct timex *" "buf" );
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.SH DESCRIPTION
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Linux uses David L. Mills' clock adjustment algorithm (see RFC\ 1305).
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The system call
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.BR adjtimex ()
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reads and optionally sets adjustment parameters for this algorithm.
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It takes a pointer to a
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.I timex
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structure, updates kernel parameters from field values,
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and returns the same structure with current kernel values.
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This structure is declared as follows:
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.PP
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.in +4n
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.nf
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struct timex {
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int modes; /* mode selector */
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long offset; /* time offset (usec) */
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long freq; /* frequency offset (scaled ppm) */
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.\" FIXME -- what is the scaling unit? 2^16 ?
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long maxerror; /* maximum error (usec) */
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long esterror; /* estimated error (usec) */
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int status; /* clock command/status */
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long constant; /* pll time constant */
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long precision; /* clock precision (usec) (read-only) */
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long tolerance; /* clock frequency tolerance (ppm)
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(read-only) */
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struct timeval time; /* current time (read-only) */
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long tick; /* usecs between clock ticks */
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};
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.fi
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.in
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.PP
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The
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.I modes
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field determines which parameters, if any, to set.
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It may contain a
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.RI bitwise- or
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combination of zero or more of the following bits:
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.PP
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.in +4n
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.nf
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#define ADJ_OFFSET 0x0001 /* time offset */
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#define ADJ_FREQUENCY 0x0002 /* frequency offset */
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#define ADJ_MAXERROR 0x0004 /* maximum time error */
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#define ADJ_ESTERROR 0x0008 /* estimated time error */
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#define ADJ_STATUS 0x0010 /* clock status */
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#define ADJ_TIMECONST 0x0020 /* pll time constant */
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#define ADJ_TICK 0x4000 /* tick value */
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#define ADJ_OFFSET_SINGLESHOT 0x8001 /* old-fashioned adjtime() */
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.fi
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.in
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.PP
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Ordinary users are restricted to a zero value for
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.IR mode .
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Only the superuser may set any parameters.
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.br
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.ne 12v
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.SH RETURN VALUE
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On success,
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.BR adjtimex ()
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returns the clock state:
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.PP
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.in +4n
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.nf
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#define TIME_OK 0 /* clock synchronized */
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#define TIME_INS 1 /* insert leap second */
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#define TIME_DEL 2 /* delete leap second */
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#define TIME_OOP 3 /* leap second in progress */
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#define TIME_WAIT 4 /* leap second has occurred */
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#define TIME_BAD 5 /* clock not synchronized */
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.fi
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.in
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.PP
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On failure,
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.BR adjtimex ()
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returns \-1 and sets
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.IR errno .
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.SH ERRORS
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.TP
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.B EFAULT
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.I buf
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does not point to writable memory.
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.TP
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.B EINVAL
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An attempt is made to set
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.I buf.offset
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to a value outside the range \-131071 to +131071,
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or to set
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.I buf.status
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to a value other than those listed above,
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or to set
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.I buf.tick
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to a value outside the range
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.RB 900000/ HZ
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to
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.RB 1100000/ HZ ,
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where
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.B HZ
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is the system timer interrupt frequency.
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.TP
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.B EPERM
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.I buf.mode
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is nonzero and the caller does not have sufficient privilege.
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Under Linux the
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.B CAP_SYS_TIME
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capability is required.
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.SH CONFORMING TO
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.BR adjtimex ()
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is Linux-specific and should not be used in programs
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intended to be portable.
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See
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.BR adjtime (3)
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for a more portable, but less flexible,
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method of adjusting the system clock.
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.SH SEE ALSO
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.BR settimeofday (2),
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.BR adjtime (3),
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.BR capabilities (7),
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.BR time (7)
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