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 .BR "#define _BSD_SOURCE" "      /* See feature_test_macros(7) */"
  35 .B #include <sys/timex.h>
  36
  37 .BI "int adjtimex(struct timex *" "buf" );
  38 .fi
  39 .SH DESCRIPTION
  40 Linux uses David L. Mills' clock adjustment algorithm (see RFC\ 5905).
  41 The system call
  42 .BR adjtimex ()
  43 reads and optionally sets adjustment parameters for this algorithm.
  44 It takes a pointer to a
  45 .I timex
  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:
  49 .PP
  50 .in +4n
  51 .nf
  52 struct timex {
  53     int  modes;       /* Mode selector */
  54     long offset;      /* Time offset; nanoseconds, if STA_NANO
  55                          status flag is set, otherwise
  56                          microseconds */
  57     long freq;        /* Frequency offset, in units of 2^-16 ppm
  58                          (parts per million) (see NOTES below) */
  59     long maxerror;    /* Maximum error (microseconds) */
  60     long esterror;    /* Estimated error (microseconds) */
  61     int  status;      /* Clock command/status */
  62     long constant;    /* PLL (phase-locked loop) time constant */
  63     long precision;   /* Clock precision (microseconds,
  64                          read-only) */
  65     long tolerance;   /* Clock frequency tolerance (ppm, read-only) */
  66     struct timeval time;
  67                       /* Current time (read-only, except for
  68                          ADJ_SETOFFSET); upon return, time.tv_usec
  69                          contains nanoseconds, if STA_NANO status
  70                          flag is set, otherwise microseconds */
  71     long tick;        /* Microseconds between clock ticks */
  72     long ppsfreq;     /* PPS (pulse per second) frequency
  73                          (2^-16 ppm (see NOTES), read-only) */
  74     long jitter;      /* PPS jitter (read-only); nanoseconds, if
  75                          STA_NANO status flag is set, otherwise
  76                          microseconds */
  77     int  shift;       /* PPS interval duration
  78                          (seconds, read-only) */
  79     long stabil;      /* PPS stability (2^-16 ppm (see NOTES), read-only) */
  80     long jitcnt;      /* PPS jitter limit exceeded (read-only) */
  81     long calcnt;      /* PPS calibration intervals (read-only) */
  82     long errcnt;      /* PPS calibration errors (read-only) */
  83     long stbcnt;      /* PPS stability limit exceeded
  84                          (read-only) */
  85     int tai;          /* TAI offset, as set by previous ADJ_TAI
  86                          operation (seconds, read-only,
  87                          since Linux 2.6.26) */
  88     /* Further padding bytes to allow for future expansion */
  89 };
  90 .fi
  91 .in
  92 .PP
  93 The
  94 .I modes
  95 field determines which parameters, if any, to set.
  96 It is a bit mask containing a
  97 .RI bitwise- or
  98 combination of zero or more of the following bits:
  99 .TP
 100 .BR ADJ_OFFSET
 101 Set time offset from
 102 .IR buf.offset .
 103 .TP
 104 .BR ADJ_FREQUENCY
 105 Set frequency offset from
 106 .IR buf.freq .
 107 .TP
 108 .BR ADJ_MAXERROR
 109 Set maximum time error from
 110 .IR buf.maxerror .
 111 .TP
 112 .BR ADJ_ESTERROR
 113 Set estimated time error from
 114 .IR buf.esterror .
 115 .TP
 116 .BR ADJ_STATUS
 117 Set clock status from
 118 .IR buf.status .
 119 .TP
 120 .BR ADJ_TIMECONST
 121 Set PLL time constant from
 122 .IR buf.constant .
 123 If the
 124 .B STA_NANO
 125 status flag (see below) is clear, the kernel adds 4 to this value.
 126 .TP
 127 .BR ADJ_SETOFFSET " (since Linux 2.6.29)"
 128 .\" commit 094aa1881fdc1b8889b442eb3511b31f3ec2b762
 129 .\" Author: Richard Cochran <richardcochran@gmail.com>
 130 Add
 131 .I buf.time
 132 to the current time.
 133 If
 134 .I buf.status
 135 includes the
 136 .B ADJ_NANO
 137 flag, then
 138 .I buf.time.tv_usec
 139 is interpreted as a nanosecond value;
 140 otherwise it is interpreted as microseconds.
 141 .TP
 142 .BR ADJ_MICRO " (since Linux 2.6.36)"
 143 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 144 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 145 Select microsecond resolution.
 146 .TP
 147 .BR ADJ_NANO " (since Linux 2.6.36)"
 148 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 149 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 150 Select nanosecond resolution.
 151 Only one of
 152 .BR ADJ_MICRO
 153 and
 154 .BR ADJ_NANO
 155 should be specified.
 156 .TP
 157 .BR ADJ_TAI " (since Linux 2.6.26)"
 158 .\" commit 153b5d054ac2d98ea0d86504884326b6777f683d
 159 Set TAI (Atomic International Time) offset from
 160 .IR buf->constant .
 161
 162 .BR ADJ_TAI
 163 should not be used in conjunction with
 164 .BR ADJ_TIMECONST ,
 165 since the latter mode also employs the
 166 .IR buf->constant
 167 field.
 168
 169 For a complete explanation of TAI
 170 and the difference between TAI and UTC, see
 171 .UR http://www.bipm.org/en/bipm/tai/tai.html
 172 .I BIPM
 173 .UE
 174 .TP
 175 .BR ADJ_TICK
 176 Set tick value from
 177 .IR buf.tick .
 178 .PP
 179 Alternatively,
 180 .I modes
 181 can be specified as either of the following (multibit mask) values,
 182 in which case other bits should not be specified in
 183 .IR modes :
 184 .\" In general, the other bits are ignored, but ADJ_OFFSET_SINGLESHOT 0x8001
 185 .\" ORed with ADJ_NANO (0x2000) gives 0xa0001 == ADJ_OFFSET_SS_READ!!
 186 .TP
 187 .BR ADJ_OFFSET_SINGLESHOT
 188 .\" In user space, ADJ_OFFSET_SINGLESHOT is 0x8001
 189 .\" In kernel space it is 0x0001, and must be ANDed with ADJ_ADJTIME (0x8000)
 190 Old-fashioned
 191 .BR adjtime ():
 192 (gradually) adjust time by value specified in
 193 .IR buf.offset ,
 194 which specifies an adjustment in microseconds.
 195 .TP
 196 .BR ADJ_OFFSET_SS_READ " (functional since Linux 2.6.28)"
 197 .\" In user space, ADJ_OFFSET_SS_READ is 0xa001
 198 .\" In kernel space there is ADJ_OFFSET_READONLY (0x2000) anded with
 199 .\" ADJ_ADJTIME (0x8000) and ADJ_OFFSET_SINGLESHOT (0x0001) to give 0xa001)
 200 Return (in
 201 .BR buf.offset )
 202 the remaining amount of time to be adjusted after an earlier
 203 .BR ADJ_OFFSET_SINGLESHOT
 204 operation.
 205 This feature was added in Linux 2.6.24,
 206 .\" commit 52bfb36050c8529d9031d2c2513b281a360922ec
 207 but did not work correctly
 208 .\" commit 916c7a855174e3b53d182b97a26b2e27a29726a1
 209 until Linux 2.6.28.
 210 .PP
 211 Ordinary users are restricted to a value of either 0 or
 212 .B ADJ_OFFSET_SS_READ
 213 for
 214 .IR modes .
 215 Only the superuser may set any parameters.
 216
 217 The
 218 .I buf.status
 219 field is a bit mask that is used to set and/or retrieve status
 220 bits associated with the NTP implementation.
 221 Some bits in the mask are both readable and settable,
 222 while others are read-only.
 223 .TP
 224 .BR STA_PLL
 225 Enable phase-locked loop (PLL) updates (read-write) via
 226 .BR ADJ_OFFSET .
 227 .TP
 228 .BR STA_PPSFREQ
 229 Enable PPS freq discipline (read-write).
 230 .TP
 231 .BR STA_PPSTIME
 232 Enable PPS time discipline (read-write).
 233 .TP
 234 .BR STA_FLL
 235 Select frequency-locked loop (FLL) mode (read-write).
 236 .TP
 237 .BR STA_INS
 238 Insert leap second (read-write).
 239 .TP
 240 .BR STA_DEL
 241 Delete leap second (read-write).
 242 .TP
 243 .BR STA_UNSYNC
 244 Clock unsynchronized (read-write).
 245 .TP
 246 .BR STA_FREQHOLD
 247 Hold frequency (read-write).
 248 .TP
 249 .BR STA_PPSSIGNAL
 250 PPS signal present (read-only).
 251 .TP
 252 .BR STA_PPSJITTER
 253 PPS signal jitter exceeded (read-only).
 254 .TP
 255 .BR STA_PPSWANDER
 256 PPS signal wander exceeded (read-only).
 257 .TP
 258 .BR STA_PPSERROR
 259 PPS signal calibration error (read-only).
 260 .TP
 261 .BR STA_CLOCKERR
 262 Clock hardware fault (read-only).
 263 .TP
 264 .BR STA_NANO " (since Linux 2.6.26)"
 265 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 266 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 267 Resolution (0 = microsecond, 1 = nanoseconds; read-only).
 268 Set via
 269 .BR ADJ_NANO ,
 270 cleared via
 271 .BR ADJ_MICRO .
 272 .TP
 273 .BR STA_MODE " (since Linux 2.6.26)"
 274 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 275 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 276 Mode (0 = Phase Locked Loop, 1 = Frequency Locked Loop; read-only).
 277 .TP
 278 .BR STA_CLK " (since Linux 2.6.26)"
 279 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 280 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 281 Clock source (0 = A, 1 = B; read-only).
 282 .PP
 283 Attempts to set read-only
 284 .I status
 285 bits are silently ignored.
 286 .SH RETURN VALUE
 287 On success,
 288 .BR adjtimex ()
 289 returns the clock state; that is, one of the following values:
 290 .TP 12
 291 .BR TIME_OK
 292 Clock synchronized.
 293 .TP
 294 .BR TIME_INS
 295 Insert leap second.
 296 .TP
 297 .BR TIME_DEL
 298 Delete leap second.
 299 .TP
 300 .BR TIME_OOP
 301 Leap second in progress.
 302 .TP
 303 .BR TIME_WAIT
 304 Leap second has occurred.
 305 .TP
 306 .BR TIME_ERROR
 307 Clock not synchronized.
 308 The symbolic name
 309 .B TIME_BAD
 310 is a synonym for
 311 .BR TIME_ERROR ,
 312 provided for backward comaptibility.
 313 .PP
 314 On failure,
 315 .BR adjtimex ()
 316 returns \-1 and sets
 317 .IR errno .
 318 .SH ERRORS
 319 .TP
 320 .B EFAULT
 321 .I buf
 322 does not point to writable memory.
 323 .TP
 324 .B EINVAL
 325 An attempt was made to set
 326 .I buf.offset
 327 to a value outside the range \-131071 to +131071,
 328 or to set
 329 .I buf.status
 330 to a value other than those listed above,
 331 or to set
 332 .I buf.tick
 333 to a value outside the range
 334 .RB 900000/ HZ
 335 to
 336 .RB 1100000/ HZ ,
 337 where
 338 .B HZ
 339 is the system timer interrupt frequency.
 340 .TP
 341 .B EPERM
 342 .I buf.modes
 343 is neither 0 nor
 344 .BR ADJ_OFFSET_SS_READ ,
 345 and the caller does not have sufficient privilege.
 346 Under Linux, the
 347 .B CAP_SYS_TIME
 348 capability is required.
 349 .SH NOTES
 350 In struct
 351 .IR timex ,
 352 .IR freq ,
 353 .IR ppsfreq ,
 354 and
 355 .I stabil
 356 are ppm (parts per million) with a 16-bits fractional part, which means that a
 357 value of 1 in one of those fields actually means 2^-16 ppm, and 2^16=65535 is
 358 1 ppm. This is the case for both input values (in the case of
 359 .IR freq )
 360 and output values.
 361 .SH CONFORMING TO
 362 .BR adjtimex ()
 363 is Linux-specific and should not be used in programs
 364 intended to be portable.
 365 See
 366 .BR adjtime (3)
 367 for a more portable, but less flexible,
 368 method of adjusting the system clock.
 369 .SH SEE ALSO
 370 .BR settimeofday (2),
 371 .BR adjtime (3),
 372 .BR capabilities (7),
 373 .BR time (7),
 374 .BR adjtimex (8)