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 2014-05-28 "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, as scaled PPM
  58                          (parts per million) */
  59 .\" FIXME What is the scaling unit of timex.freq?  2^16 ?
  60     long maxerror;    /* Maximum error (microseconds) */
  61     long esterror;    /* Estimated error (microseconds) */
  62     int  status;      /* Clock command/status */
  63     long constant;    /* PLL (phase-locked loop) time constant */
  64     long precision;   /* Clock precision (microseconds,
  65                          read-only) */
  66     long tolerance;   /* Clock frequency tolerance (PPM,
  67                          read-only) */
  68     struct timeval time;
  69                       /* Current time (read-only, except for
  70                          ADJ_SETOFFSET); upon return, time.tv_usec
  71                          contains nanoseconds, if STA_NANO status
  72                          flag is set, otherwise microseconds */
  73     long tick;        /* Microseconds between clock ticks */
  74     long ppsfreq;     /* PPS (pulse per second) frequency
  75                          (scaled PPM, read-only) */
  76     long jitter;      /* PPS jitter (read-only); nanoseconds, if
  77                          STA_NANO status flag is set, otherwise
  78                          microseconds */
  79     int  shift;       /* PPS interval duration
  80                          (seconds, read-only) */
  81     long stabil;      /* PPS stability (scaled PPM, read-only) */
  82     long jitcnt;      /* PPS jitter limit exceeded (read-only) */
  83     long calcnt;      /* PPS calibration intervals (read-only) */
  84     long errcnt;      /* PPS calibration errors (read-only) */
  85     long stbcnt;      /* PPS stability limit exceeded
  86                          (read-only) */
  87     int tai;          /* TAI offset, as set by previous ADJ_TAI
  88                          operation (seconds, read-only,
  89                          since Linux 2.6.26) */
  90     /* Further padding bytes to allow for future expansion */
  91 };
  92 .fi
  93 .in
  94 .PP
  95 The
  96 .I modes
  97 field determines which parameters, if any, to set.
  98 It is a bit mask containing a
  99 .RI bitwise- or
 100 combination of zero or more of the following bits:
 101 .TP
 102 .BR ADJ_OFFSET
 103 Set time offset from
 104 .IR buf.offset .
 105 .TP
 106 .BR ADJ_FREQUENCY
 107 Set frequency offset from
 108 .IR buf.freq .
 109 .TP
 110 .BR ADJ_MAXERROR
 111 Set maximum time error from
 112 .IR buf.maxerror .
 113 .TP
 114 .BR ADJ_ESTERROR
 115 Set estimated time error from
 116 .IR buf.esterror .
 117 .TP
 118 .BR ADJ_STATUS
 119 Set clock status from
 120 .IR buf.status .
 121 .TP
 122 .BR ADJ_TIMECONST
 123 Set PLL time constant from
 124 .IR buf.constant .
 125 If the
 126 .B STA_NANO
 127 status flag (see below) is clear, the kernel adds 4 to this value.
 128 .TP
 129 .BR ADJ_SETOFFSET " (since Linux 2.6.29)"
 130 .\" commit 094aa1881fdc1b8889b442eb3511b31f3ec2b762
 131 .\" Author: Richard Cochran <richardcochran@gmail.com>
 132 Add
 133 .I buf.time
 134 to the current time.
 135 If
 136 .I buf.status
 137 includes the
 138 .B ADJ_NANO
 139 flag, then
 140 .I buf.time.tv_usec
 141 is interpreted as a nanosecond value;
 142 otherwise it is interpreted as microseconds.
 143 .TP
 144 .BR ADJ_MICRO " (since Linux 2.6.36)"
 145 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 146 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 147 Select microsecond resolution.
 148 .TP
 149 .BR ADJ_NANO " (since Linux 2.6.36)"
 150 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 151 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 152 Select nanosecond resolution.
 153 Only one of
 154 .BR ADJ_MICRO
 155 and
 156 .BR ADJ_NANO
 157 should be specified.
 158 .TP
 159 .BR ADJ_TAI " (since Linux 2.6.26)"
 160 .\" commit 153b5d054ac2d98ea0d86504884326b6777f683d
 161 Set TAI (Atomic International Time) offset from
 162 .IR buf->constant .
 163
 164 .BR ADJ_TAI
 165 should not be used in conjunction with
 166 .BR ADJ_TIMECONST ,
 167 since the latter mode also employs the
 168 .IR buf->constant
 169 field.
 170
 171 For a complete explanation of TAI
 172 and the difference between TAI and UTC, see
 173 .UR http://www.bipm.org/en/bipm/tai/tai.html
 174 .I BIPM
 175 .UE
 176 .TP
 177 .BR ADJ_TICK
 178 Set tick value from
 179 .IR buf.tick .
 180 .PP
 181 Alternatively,
 182 .I modes
 183 can be specified as either of the following (multibit mask) values,
 184 in which case other bits should not be specified in
 185 .IR modes :
 186 .\" In general, the other bits are ignored, but ADJ_OFFSET_SINGLESHOT 0x8001
 187 .\" ORed with ADJ_NANO (0x2000) gives 0xa0001 == ADJ_OFFSET_SS_READ!!
 188 .TP
 189 .BR ADJ_OFFSET_SINGLESHOT
 190 .\" In user space, ADJ_OFFSET_SINGLESHOT is 0x8001
 191 .\" In kernel space it is 0x0001, and must be ANDed with ADJ_ADJTIME (0x8000)
 192 Old-fashioned
 193 .BR adjtime ():
 194 (gradually) adjust time by value specified in
 195 .IR buf.offset ,
 196 which specifies an adjustment in microseconds.
 197 .TP
 198 .BR ADJ_OFFSET_SS_READ " (functional since Linux 2.6.28)"
 199 .\" In user space, ADJ_OFFSET_SS_READ is 0xa001
 200 .\" In kernel space there is ADJ_OFFSET_READONLY (0x2000) anded with
 201 .\" ADJ_ADJTIME (0x8000) and ADJ_OFFSET_SINGLESHOT (0x0001) to give 0xa001)
 202 Return (in
 203 .BR buf.offset )
 204 the remaining amount of time to be adjusted after an earlier
 205 .BR ADJ_OFFSET_SINGLESHOT
 206 operation.
 207 This feature was added in Linux 2.6.24,
 208 .\" commit 52bfb36050c8529d9031d2c2513b281a360922ec
 209 but did not work correctly
 210 .\" commit 916c7a855174e3b53d182b97a26b2e27a29726a1
 211 until Linux 2.6.28.
 212 .PP
 213 Ordinary users are restricted to a value of either 0 or
 214 .B ADJ_OFFSET_SS_READ
 215 for
 216 .IR modes .
 217 Only the superuser may set any parameters.
 218
 219 The
 220 .I buf.status
 221 field is a bit mask that is used to set and/or retrieve status
 222 bits associated with the NTP implementation.
 223 Some bits in the mask are both readable and settable,
 224 while others are read-only.
 225 .TP
 226 .BR STA_PLL
 227 Enable phase-locked loop (PLL) updates (read-write) via
 228 .BR ADJ_OFFSET .
 229 .TP
 230 .BR STA_PPSFREQ
 231 Enable PPS freq discipline (read-write).
 232 .TP
 233 .BR STA_PPSTIME
 234 Enable PPS time discipline (read-write).
 235 .TP
 236 .BR STA_FLL
 237 Select frequency-locked loop (FLL) mode (read-write).
 238 .TP
 239 .BR STA_INS
 240 Insert leap second (read-write).
 241 .TP
 242 .BR STA_DEL
 243 Delete leap second (read-write).
 244 .TP
 245 .BR STA_UNSYNC
 246 Clock unsynchronized (read-write).
 247 .TP
 248 .BR STA_FREQHOLD
 249 Hold frequency (read-write).
 250 .TP
 251 .BR STA_PPSSIGNAL
 252 PPS signal present (read-only).
 253 .TP
 254 .BR STA_PPSJITTER
 255 PPS signal jitter exceeded (read-only).
 256 .TP
 257 .BR STA_PPSWANDER
 258 PPS signal wander exceeded (read-only).
 259 .TP
 260 .BR STA_PPSERROR
 261 PPS signal calibration error (read-only).
 262 .TP
 263 .BR STA_CLOCKERR
 264 Clock hardware fault (read-only).
 265 .TP
 266 .BR STA_NANO " (since Linux 2.6.26)"
 267 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 268 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 269 Resolution (0 = microsecond, 1 = nanoseconds; read-only).
 270 Set via
 271 .BR ADJ_NANO ,
 272 cleared via
 273 .BR ADJ_MICRO .
 274 .TP
 275 .BR STA_MODE " (since Linux 2.6.26)"
 276 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 277 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 278 Mode (0 = Phase Locked Loop, 1 = Frequency Locked Loop; read-only).
 279 .TP
 280 .BR STA_CLK " (since Linux 2.6.26)"
 281 .\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
 282 .\" Author: Roman Zippel <zippel@linux-m68k.org>
 283 Clock source (0 = A, 1 = B; read-only).
 284 .PP
 285 Attempts to set read-only
 286 .I status
 287 bits are silently ignored.
 288 .SH RETURN VALUE
 289 On success,
 290 .BR adjtimex ()
 291 returns the clock state; that is, one of the following values:
 292 .TP 12
 293 .BR TIME_OK
 294 Clock synchronized.
 295 .TP
 296 .BR TIME_INS
 297 Insert leap second.
 298 .TP
 299 .BR TIME_DEL
 300 Delete leap second.
 301 .TP
 302 .BR TIME_OOP
 303 Leap second in progress.
 304 .TP
 305 .BR TIME_WAIT
 306 Leap second has occurred.
 307 .TP
 308 .BR TIME_BAD
 309 Clock not synchronized.
 310 .PP
 311 On failure,
 312 .BR adjtimex ()
 313 returns \-1 and sets
 314 .IR errno .
 315 .SH ERRORS
 316 .TP
 317 .B EFAULT
 318 .I buf
 319 does not point to writable memory.
 320 .TP
 321 .B EINVAL
 322 An attempt was made to set
 323 .I buf.offset
 324 to a value outside the range \-131071 to +131071,
 325 or to set
 326 .I buf.status
 327 to a value other than those listed above,
 328 or to set
 329 .I buf.tick
 330 to a value outside the range
 331 .RB 900000/ HZ
 332 to
 333 .RB 1100000/ HZ ,
 334 where
 335 .B HZ
 336 is the system timer interrupt frequency.
 337 .TP
 338 .B EPERM
 339 .I buf.modes
 340 is neither 0 nor
 341 .BR ADJ_OFFSET_SS_READ ,
 342 and the caller does not have sufficient privilege.
 343 Under Linux, the
 344 .B CAP_SYS_TIME
 345 capability is required.
 346 .SH CONFORMING TO
 347 .BR adjtimex ()
 348 is Linux-specific and should not be used in programs
 349 intended to be portable.
 350 See
 351 .BR adjtime (3)
 352 for a more portable, but less flexible,
 353 method of adjusting the system clock.
 354 .SH SEE ALSO
 355 .BR settimeofday (2),
 356 .BR adjtime (3),
 357 .BR capabilities (7),
 358 .BR time (7),
 359 .BR adjtimex (8)