1 .\" Copyright (c) 1995 Michael Chastain (mec@shell.portal.com), 15 April 1995.
2 .\" and Copyright (C) 2014 Michael Kerrisk <mtk.manpages@gmail.com>
4 .\" %%%LICENSE_START(GPLv2+_DOC_FULL)
5 .\" This is free documentation; you can redistribute it and/or
6 .\" modify it under the terms of the GNU General Public License as
7 .\" published by the Free Software Foundation; either version 2 of
8 .\" the License, or (at your option) any later version.
10 .\" The GNU General Public License's references to "object code"
11 .\" and "executables" are to be interpreted as the output of any
12 .\" document formatting or typesetting system, including
13 .\" intermediate and printed output.
15 .\" This manual is distributed in the hope that it will be useful,
16 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
17 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 .\" GNU General Public License for more details.
20 .\" You should have received a copy of the GNU General Public
21 .\" License along with this manual; if not, see
22 .\" <http://www.gnu.org/licenses/>.
25 .\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
26 .\" Modified 1997-07-30 by Paul Slootman <paul@wurtel.demon.nl>
27 .\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>
29 .TH ADJTIMEX 2 2014-12-31 "Linux" "Linux Programmer's Manual"
31 adjtimex \- tune kernel clock
34 .BR "#define _BSD_SOURCE" " /* See feature_test_macros(7) */"
35 .B #include <sys/timex.h>
37 .BI "int adjtimex(struct timex *" "buf" );
40 Linux uses David L. Mills' clock adjustment algorithm (see RFC\ 5905).
43 reads and optionally sets adjustment parameters for this algorithm.
44 It takes a pointer to a
46 structure, updates kernel parameters from field values,
47 and returns the same structure with current kernel values.
48 This structure is declared as follows:
53 int modes; /* Mode selector */
54 long offset; /* Time offset; nanoseconds, if STA_NANO
55 status flag is set, otherwise microseconds */
56 long freq; /* Frequency offset, in units of 2^-16 ppm
57 (parts per million, see NOTES below) */
58 long maxerror; /* Maximum error (microseconds) */
59 long esterror; /* Estimated error (microseconds) */
60 int status; /* Clock command/status */
61 long constant; /* PLL (phase-locked loop) time constant */
62 long precision; /* Clock precision (microseconds, read-only) */
63 long tolerance; /* Clock frequency tolerance (ppm, read-only) */
65 /* Current time (read-only, except for
66 ADJ_SETOFFSET); upon return, time.tv_usec
67 contains nanoseconds, if STA_NANO status
68 flag is set, otherwise microseconds */
69 long tick; /* Microseconds between clock ticks */
70 long ppsfreq; /* PPS (pulse per second) frequency (in units
71 of 2^-16 ppm\-\-see NOTES, read-only) */
72 long jitter; /* PPS jitter (read-only); nanoseconds, if
73 STA_NANO status flag is set, otherwise
75 int shift; /* PPS interval duration (seconds, read-only) */
76 long stabil; /* PPS stability (2^-16 ppm\-\-see NOTES,
78 long jitcnt; /* PPS jitter limit exceeded (read-only) */
79 long calcnt; /* PPS calibration intervals (read-only) */
80 long errcnt; /* PPS calibration errors (read-only) */
81 long stbcnt; /* PPS stability limit exceeded (read-only) */
82 int tai; /* TAI offset, as set by previous ADJ_TAI
83 operation (seconds, read-only,
84 since Linux 2.6.26) */
85 /* Further padding bytes to allow for future expansion */
92 field determines which parameters, if any, to set.
93 It is a bit mask containing a
95 combination of zero or more of the following bits:
102 Set frequency offset from
106 Set maximum time error from
110 Set estimated time error from
114 Set clock status from
118 Set PLL time constant from
122 status flag (see below) is clear, the kernel adds 4 to this value.
124 .BR ADJ_SETOFFSET " (since Linux 2.6.29)"
125 .\" commit 094aa1881fdc1b8889b442eb3511b31f3ec2b762
126 .\" Author: Richard Cochran <richardcochran@gmail.com>
136 is interpreted as a nanosecond value;
137 otherwise it is interpreted as microseconds.
139 .BR ADJ_MICRO " (since Linux 2.6.36)"
140 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
141 .\" Author: Roman Zippel <zippel@linux-m68k.org>
142 Select microsecond resolution.
144 .BR ADJ_NANO " (since Linux 2.6.36)"
145 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
146 .\" Author: Roman Zippel <zippel@linux-m68k.org>
147 Select nanosecond resolution.
154 .BR ADJ_TAI " (since Linux 2.6.26)"
155 .\" commit 153b5d054ac2d98ea0d86504884326b6777f683d
156 Set TAI (Atomic International Time) offset from
160 should not be used in conjunction with
162 since the latter mode also employs the
166 For a complete explanation of TAI
167 and the difference between TAI and UTC, see
168 .UR http://www.bipm.org/en/bipm/tai/tai.html
178 can be specified as either of the following (multibit mask) values,
179 in which case other bits should not be specified in
181 .\" In general, the other bits are ignored, but ADJ_OFFSET_SINGLESHOT 0x8001
182 .\" ORed with ADJ_NANO (0x2000) gives 0xa0001 == ADJ_OFFSET_SS_READ!!
184 .BR ADJ_OFFSET_SINGLESHOT
185 .\" In user space, ADJ_OFFSET_SINGLESHOT is 0x8001
186 .\" In kernel space it is 0x0001, and must be ANDed with ADJ_ADJTIME (0x8000)
189 (gradually) adjust time by value specified in
191 which specifies an adjustment in microseconds.
193 .BR ADJ_OFFSET_SS_READ " (functional since Linux 2.6.28)"
194 .\" In user space, ADJ_OFFSET_SS_READ is 0xa001
195 .\" In kernel space there is ADJ_OFFSET_READONLY (0x2000) anded with
196 .\" ADJ_ADJTIME (0x8000) and ADJ_OFFSET_SINGLESHOT (0x0001) to give 0xa001)
199 the remaining amount of time to be adjusted after an earlier
200 .BR ADJ_OFFSET_SINGLESHOT
202 This feature was added in Linux 2.6.24,
203 .\" commit 52bfb36050c8529d9031d2c2513b281a360922ec
204 but did not work correctly
205 .\" commit 916c7a855174e3b53d182b97a26b2e27a29726a1
208 Ordinary users are restricted to a value of either 0 or
209 .B ADJ_OFFSET_SS_READ
212 Only the superuser may set any parameters.
216 field is a bit mask that is used to set and/or retrieve status
217 bits associated with the NTP implementation.
218 Some bits in the mask are both readable and settable,
219 while others are read-only.
222 Enable phase-locked loop (PLL) updates (read-write) via
226 Enable PPS freq discipline (read-write).
229 Enable PPS time discipline (read-write).
232 Select frequency-locked loop (FLL) mode (read-write).
235 Insert leap second (read-write).
238 Delete leap second (read-write).
241 Clock unsynchronized (read-write).
244 Hold frequency (read-write).
247 PPS signal present (read-only).
250 PPS signal jitter exceeded (read-only).
253 PPS signal wander exceeded (read-only).
256 PPS signal calibration error (read-only).
259 Clock hardware fault (read-only).
261 .BR STA_NANO " (since Linux 2.6.26)"
262 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
263 .\" Author: Roman Zippel <zippel@linux-m68k.org>
264 Resolution (0 = microsecond, 1 = nanoseconds; read-only).
270 .BR STA_MODE " (since Linux 2.6.26)"
271 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
272 .\" Author: Roman Zippel <zippel@linux-m68k.org>
273 Mode (0 = Phase Locked Loop, 1 = Frequency Locked Loop; read-only).
275 .BR STA_CLK " (since Linux 2.6.26)"
276 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
277 .\" Author: Roman Zippel <zippel@linux-m68k.org>
278 Clock source (0 = A, 1 = B; read-only).
279 .\" FIXME It would be helpful to have some explanation of what
280 .\" "Clock source" is.
282 Attempts to set read-only
284 bits are silently ignored.
288 returns the clock state; that is, one of the following values:
300 Leap second in progress.
303 Leap second has occurred.
306 Clock not synchronized.
311 provided for backward compatibility.
321 does not point to writable memory.
324 An attempt was made to set
326 to a value outside the range \-131071 to +131071,
329 to a value other than those listed above,
332 to a value outside the range
338 is the system timer interrupt frequency.
343 .BR ADJ_OFFSET_SS_READ ,
344 and the caller does not have sufficient privilege.
347 capability is required.
355 are ppm (parts per million) with a 16-bit fractional part,
356 which means that a value of 1 in one of those fields
357 actually means 2^-16 ppm, and 2^16=65536 is 1 ppm.
358 This is the case for both input values (in the case of
363 is Linux-specific and should not be used in programs
364 intended to be portable.
367 for a more portable, but less flexible,
368 method of adjusting the system clock.
370 .BR settimeofday (2),
372 .BR capabilities (7),
376 This page is part of release 3.78 of the Linux
379 A description of the project,
380 information about reporting bugs,
381 and the latest version of this page,
383 \%http://www.kernel.org/doc/man\-pages/.