man2/adjtimex.2

   1 .\" Copyright (c) 1995 Michael Chastain (mec@shell.portal.com), 15 April 1995.
   2 .\" and Copyright (C) 2014 Michael Kerrisk <mtk.manpages@gmail.com>
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  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>
  28 .\"
  29 .TH ADJTIMEX 2 2014-12-31 "Linux" "Linux Programmer's Manual"
  30 .SH NAME
  31 adjtimex \- tune kernel clock
  32 .SH SYNOPSIS
  33 .nf
  34 .B #include <sys/timex.h>
  35
  36 .BI "int adjtimex(struct timex *" "buf" );
  37 .fi
  38 .SH DESCRIPTION
  39 Linux uses David L. Mills' clock adjustment algorithm (see RFC\ 5905).
  40 The system call
  41 .BR adjtimex ()
  42 reads and optionally sets adjustment parameters for this algorithm.
  43 It takes a pointer to a
  44 .I timex
  45 structure, updates kernel parameters from field values,
  46 and returns the same structure with current kernel values.
  47 This structure is declared as follows:
  48 .PP
  49 .in +4n
  50 .nf
  51 struct timex {
  52     int  modes;      /* Mode selector */
  53     long offset;     /* Time offset; nanoseconds, if STA_NANO
  54                         status flag is set, otherwise microseconds */
  55     long freq;       /* Frequency offset, in units of 2^-16 ppm
  56                         (parts per million, see NOTES below) */
  57     long maxerror;   /* Maximum error (microseconds) */
  58     long esterror;   /* Estimated error (microseconds) */
  59     int  status;     /* Clock command/status */
  60     long constant;   /* PLL (phase-locked loop) time constant */
  61     long precision;  /* Clock precision (microseconds, read-only) */
  62     long tolerance;  /* Clock frequency tolerance (ppm, read-only) */
  63     struct timeval time;
  64                      /* Current time (read-only, except for
  65                         ADJ_SETOFFSET); upon return, time.tv_usec
  66                         contains nanoseconds, if STA_NANO status
  67                         flag is set, otherwise microseconds */
  68     long tick;       /* Microseconds between clock ticks */
  69     long ppsfreq;    /* PPS (pulse per second) frequency (in units
  70                         of 2^-16 ppm\-\-see NOTES, read-only) */
  71     long jitter;     /* PPS jitter (read-only); nanoseconds, if
  72                         STA_NANO status flag is set, otherwise
  73                         microseconds */
  74     int  shift;      /* PPS interval duration (seconds, read-only) */
  75     long stabil;     /* PPS stability (2^-16 ppm\-\-see NOTES,
  76                         read-only) */
  77     long jitcnt;     /* PPS jitter limit exceeded (read-only) */
  78     long calcnt;     /* PPS calibration intervals (read-only) */
  79     long errcnt;     /* PPS calibration errors (read-only) */
  80     long stbcnt;     /* PPS stability limit exceeded (read-only) */
  81     int tai;         /* TAI offset, as set by previous ADJ_TAI
  82                         operation (seconds, read-only,
  83                         since Linux 2.6.26) */
  84     /* Further padding bytes to allow for future expansion */
  85 };
  86 .fi
  87 .in
  88 .PP
  89 The
  90 .I modes
  91 field determines which parameters, if any, to set.
  92 It is a bit mask containing a
  93 .RI bitwise- or
  94 combination of zero or more of the following bits:
  95 .TP
  96 .BR ADJ_OFFSET
  97 Set time offset from
  98 .IR buf.offset .
  99 .TP
 100 .BR ADJ_FREQUENCY
 101 Set frequency offset from
 102 .IR buf.freq .
 103 .TP
 104 .BR ADJ_MAXERROR
 105 Set maximum time error from
 106 .IR buf.maxerror .
 107 .TP
 108 .BR ADJ_ESTERROR
 109 Set estimated time error from
 110 .IR buf.esterror .
 111 .TP
 112 .BR ADJ_STATUS
 113 Set clock status from
 114 .IR buf.status .
 115 .TP
 116 .BR ADJ_TIMECONST
 117 Set PLL time constant from
 118 .IR buf.constant .
 119 If the
 120 .B STA_NANO
 121 status flag (see below) is clear, the kernel adds 4 to this value.
 122 .TP
 123 .BR ADJ_SETOFFSET " (since Linux 2.6.29)"
 124 .\" commit 094aa1881fdc1b8889b442eb3511b31f3ec2b762
 125 .\" Author: Richard Cochran <richardcochran@gmail.com>
 126 Add
 127 .I buf.time
 128 to the current time.
 129 If
 130 .I buf.status
 131 includes the
 132 .B ADJ_NANO
 133 flag, then
 134 .I buf.time.tv_usec
 135 is interpreted as a nanosecond value;
 136 otherwise it is interpreted as microseconds.
 137 .TP
 138 .BR ADJ_MICRO " (since Linux 2.6.36)"
 139 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 140 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 141 Select microsecond resolution.
 142 .TP
 143 .BR ADJ_NANO " (since Linux 2.6.36)"
 144 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 145 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 146 Select nanosecond resolution.
 147 Only one of
 148 .BR ADJ_MICRO
 149 and
 150 .BR ADJ_NANO
 151 should be specified.
 152 .TP
 153 .BR ADJ_TAI " (since Linux 2.6.26)"
 154 .\" commit 153b5d054ac2d98ea0d86504884326b6777f683d
 155 Set TAI (Atomic International Time) offset from
 156 .IR buf->constant .
 157
 158 .BR ADJ_TAI
 159 should not be used in conjunction with
 160 .BR ADJ_TIMECONST ,
 161 since the latter mode also employs the
 162 .IR buf->constant
 163 field.
 164
 165 For a complete explanation of TAI
 166 and the difference between TAI and UTC, see
 167 .UR http://www.bipm.org/en/bipm/tai/tai.html
 168 .I BIPM
 169 .UE
 170 .TP
 171 .BR ADJ_TICK
 172 Set tick value from
 173 .IR buf.tick .
 174 .PP
 175 Alternatively,
 176 .I modes
 177 can be specified as either of the following (multibit mask) values,
 178 in which case other bits should not be specified in
 179 .IR modes :
 180 .\" In general, the other bits are ignored, but ADJ_OFFSET_SINGLESHOT 0x8001
 181 .\" ORed with ADJ_NANO (0x2000) gives 0xa0001 == ADJ_OFFSET_SS_READ!!
 182 .TP
 183 .BR ADJ_OFFSET_SINGLESHOT
 184 .\" In user space, ADJ_OFFSET_SINGLESHOT is 0x8001
 185 .\" In kernel space it is 0x0001, and must be ANDed with ADJ_ADJTIME (0x8000)
 186 Old-fashioned
 187 .BR adjtime ():
 188 (gradually) adjust time by value specified in
 189 .IR buf.offset ,
 190 which specifies an adjustment in microseconds.
 191 .TP
 192 .BR ADJ_OFFSET_SS_READ " (functional since Linux 2.6.28)"
 193 .\" In user space, ADJ_OFFSET_SS_READ is 0xa001
 194 .\" In kernel space there is ADJ_OFFSET_READONLY (0x2000) anded with
 195 .\" ADJ_ADJTIME (0x8000) and ADJ_OFFSET_SINGLESHOT (0x0001) to give 0xa001)
 196 Return (in
 197 .IR buf.offset )
 198 the remaining amount of time to be adjusted after an earlier
 199 .BR ADJ_OFFSET_SINGLESHOT
 200 operation.
 201 This feature was added in Linux 2.6.24,
 202 .\" commit 52bfb36050c8529d9031d2c2513b281a360922ec
 203 but did not work correctly
 204 .\" commit 916c7a855174e3b53d182b97a26b2e27a29726a1
 205 until Linux 2.6.28.
 206 .PP
 207 Ordinary users are restricted to a value of either 0 or
 208 .B ADJ_OFFSET_SS_READ
 209 for
 210 .IR modes .
 211 Only the superuser may set any parameters.
 212
 213 The
 214 .I buf.status
 215 field is a bit mask that is used to set and/or retrieve status
 216 bits associated with the NTP implementation.
 217 Some bits in the mask are both readable and settable,
 218 while others are read-only.
 219 .TP
 220 .BR STA_PLL
 221 Enable phase-locked loop (PLL) updates (read-write) via
 222 .\" FIXME Any pointer to further information about what this means?
 223 .\"       (It was not immediately obvious from a scan of the RFC, whether
 224 .\"       this is described in the RFC.)
 225 .BR ADJ_OFFSET .
 226 .TP
 227 .BR STA_PPSFREQ
 228 Enable PPS freq discipline (read-write).
 229 .\" FIXME Any pointer to further information about what this means?
 230 .\"       (It was not immediately obvious from a scan of the RFC, whether
 231 .\"       this is described in the RFC.)
 232 .TP
 233 .BR STA_PPSTIME
 234 Enable PPS time discipline (read-write).
 235 .\" FIXME Any pointer to further information about what this means?
 236 .\"       (It was not immediately obvious from a scan of the RFC, whether
 237 .\"       this is described in the RFC.)
 238 .TP
 239 .BR STA_FLL
 240 Select frequency-locked loop (FLL) mode (read-write).
 241 .\" FIXME Any pointer to further information about what this means?
 242 .\"       (It was not immediately obvious from a scan of the RFC, whether
 243 .\"       this is described in the RFC.)
 244 .TP
 245 .BR STA_INS
 246 Insert leap second (read-write).
 247 .\" FIXME Is the following correct?
 248 .\"     Insert a leap second after the last second of the day.
 249 .\"     That is, at 24:00:00, set the clock 1 second back, thus extending
 250 .\"     the last  minute of the day by one second.
 251 .\"     Leap second insertion will occur each day, so long as this flag
 252 .\"     remains set.
 253 .TP
 254 .BR STA_DEL
 255 Delete leap second (read-write).
 256 .\" FIXME Is the following correct?
 257 .\"     Delete a leap second at the last second of the leap day.
 258 .\"     That is, at 23:5:59, add one extra second to the clock.
 259 .\"     Leap second deletion will occur each day, so long as this flag
 260 .\"     remains set.
 261 .\" FIXME Does there need to be a statement that it is nonsensical to set
 262 .\"     to set both STA_INS and STA_DEL?
 263 .TP
 264 .BR STA_UNSYNC
 265 Clock unsynchronized (read-write).
 266 .TP
 267 .BR STA_FREQHOLD
 268 Hold frequency (read-write).
 269 .\" FIXME Any pointer to further information about what this means?
 270 .\"       (It was not immediately obvious from a scan of the RFC, whether
 271 .\"       this is described in the RFC.)
 272 .TP
 273 .BR STA_PPSSIGNAL
 274 PPS signal present (read-only).
 275 .\" FIXME Any pointer to further information about what this means?
 276 .\"       (It was not immediately obvious from a scan of the RFC, whether
 277 .\"       this is described in the RFC.)
 278 .TP
 279 .BR STA_PPSJITTER
 280 PPS signal jitter exceeded (read-only).
 281 .\" FIXME Any pointer to further information about what this means?
 282 .\"       (It was not immediately obvious from a scan of the RFC, whether
 283 .\"       this is described in the RFC.)
 284 .TP
 285 .BR STA_PPSWANDER
 286 PPS signal wander exceeded (read-only).
 287 .\" FIXME Any pointer to further information about what this means?
 288 .\"       (It was not immediately obvious from a scan of the RFC, whether
 289 .\"       this is described in the RFC.)
 290 .TP
 291 .BR STA_PPSERROR
 292 PPS signal calibration error (read-only).
 293 .\" FIXME Any pointer to further information about what this means?
 294 .\"       (It was not immediately obvious from a scan of the RFC, whether
 295 .\"       this is described in the RFC.)
 296 .TP
 297 .BR STA_CLOCKERR
 298 Clock hardware fault (read-only).
 299 .\" FIXME Any pointer to further information about what this means?
 300 .\"       (It was not immediately obvious from a scan of the RFC, whether
 301 .\"       this is described in the RFC.)
 302 .TP
 303 .BR STA_NANO " (since Linux 2.6.26)"
 304 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 305 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 306 Resolution (0 = microsecond, 1 = nanoseconds; read-only).
 307 Set via
 308 .BR ADJ_NANO ,
 309 cleared via
 310 .BR ADJ_MICRO .
 311 .TP
 312 .BR STA_MODE " (since Linux 2.6.26)"
 313 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 314 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 315 Mode (0 = Phase Locked Loop, 1 = Frequency Locked Loop; read-only).
 316 .TP
 317 .BR STA_CLK " (since Linux 2.6.26)"
 318 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 319 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 320 Clock source (0 = A, 1 = B; read-only).
 321 .\" FIXME It would be helpful to have some explanation of what
 322 .\"       "Clock source" is.
 323 .PP
 324 Attempts to set read-only
 325 .I status
 326 bits are silently ignored.
 327 .SH RETURN VALUE
 328 On success,
 329 .BR adjtimex ()
 330 returns the clock state; that is, one of the following values:
 331 .TP 12
 332 .BR TIME_OK
 333 Clock synchronized.
 334 .TP
 335 .BR TIME_INS
 336 Insert leap second.
 337 .\" FIXME Is the following correct:
 338 .\"       Indicates that a leap second will be added at the end of the day
 339 .TP
 340 .BR TIME_DEL
 341 Delete leap second.
 342 .\" FIXME Is the following correct:
 343 .\"       Indicates that a leap second will be deleted at the end of the day
 344 .TP
 345 .BR TIME_OOP
 346 Leap second in progress.
 347 .\" FIXME Is the following correct:
 348 .\"       Indicates that we are currently in the middle of the leap second
 349 .\"       that is being added at the end of the day (as a result of STA_INS)
 350 .TP
 351 .BR TIME_WAIT
 352 Leap second has occurred.
 353 .\" FIXME Is the following correct:
 354 .\"       Indicates that a leap second has just been added or deleted
 355 .\"       during the previous second
 356 .TP
 357 .BR TIME_ERROR
 358 Clock not synchronized.
 359 .\" FIXME Should more be said about how the TIME_ERROR state can occur?
 360 The symbolic name
 361 .B TIME_BAD
 362 is a synonym for
 363 .BR TIME_ERROR ,
 364 provided for backward compatibility.
 365 Note that starting with Linux 3.4,
 366 .\" commit 6b43ae8a619d17c4935c3320d2ef9e92bdeed05d changed to asynchronous
 367 .\"  operation, so we can no longer rely on the return code.
 368 the call operates asynchronously and the return value usually will
 369 not reflect a state change caused by the call itself.
 370 .PP
 371 On failure,
 372 .BR adjtimex ()
 373 returns \-1 and sets
 374 .IR errno .
 375 .SH ERRORS
 376 .TP
 377 .B EFAULT
 378 .I buf
 379 does not point to writable memory.
 380 .TP
 381 .BR EINVAL " (kernels before Linux 2.6.26)"
 382 An attempt was made to set
 383 .I buf.offset
 384 to a value outside the permitted range.
 385 In kernels before Linux 2.0, the permitted range was (\-131072, +131072).
 386 From Linux 2.0 onwards, the permitted range was (\-512000, +512000).
 387 .TP
 388 .B EINVAL
 389 An attempt was made to set
 390 .I buf.status
 391 to a value other than those listed above.
 392 .TP
 393 .B EINVAL
 394 An attempt was made to set
 395 .I buf.tick
 396 to a value outside the range
 397 .RB 900000/ HZ
 398 to
 399 .RB 1100000/ HZ ,
 400 where
 401 .B HZ
 402 is the system timer interrupt frequency.
 403 .TP
 404 .B EPERM
 405 .I buf.modes
 406 is neither 0 nor
 407 .BR ADJ_OFFSET_SS_READ ,
 408 and the caller does not have sufficient privilege.
 409 Under Linux, the
 410 .B CAP_SYS_TIME
 411 capability is required.
 412 .SH NOTES
 413 In struct
 414 .IR timex ,
 415 .IR freq ,
 416 .IR ppsfreq ,
 417 and
 418 .I stabil
 419 are ppm (parts per million) with a 16-bit fractional part,
 420 which means that a value of 1 in one of those fields
 421 actually means 2^-16 ppm, and 2^16=65536 is 1 ppm.
 422 This is the case for both input values (in the case of
 423 .IR freq )
 424 and output values.
 425 .SH CONFORMING TO
 426 .BR adjtimex ()
 427 is Linux-specific and should not be used in programs
 428 intended to be portable.
 429 See
 430 .BR adjtime (3)
 431 for a more portable, but less flexible,
 432 method of adjusting the system clock.
 433 .SH SEE ALSO
 434 .BR settimeofday (2),
 435 .BR adjtime (3),
 436 .BR capabilities (7),
 437 .BR time (7),
 438 .BR adjtimex (8)