man2/adjtimex.2

   1 .\" Copyright (c) 1995 Michael Chastain (mec@shell.portal.com), 15 April 1995.
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  23 .\"
  24 .\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
  25 .\" Modified 1997-07-30 by Paul Slootman <paul@wurtel.demon.nl>
  26 .\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>
  27 .\"
  28 .\" FIXME Document ADJ_MICRO and ADJ_NANO (added in Linux 2.6.26)
  29 .\"             commit eea83d896e318bda54be2d2770d2c5d6668d11db
  30 .\"             Author: Roman Zippel <zippel@linux-m68k.org>
  31 .\"
  32 .\" FIXME Document ADJ_SETOFFSET (added in Linux 2.6.39)
  33 .\"             commit 094aa1881fdc1b8889b442eb3511b31f3ec2b762
  34 .\"             Author: Richard Cochran <richardcochran@gmail.com>
  35 .\"
  36 .TH ADJTIMEX 2 2014-05-28 "Linux" "Linux Programmer's Manual"
  37 .SH NAME
  38 adjtimex \- tune kernel clock
  39 .SH SYNOPSIS
  40 .nf
  41 .BR "#define _BSD_SOURCE" "      /* See feature_test_macros(7) */"
  42 .B #include <sys/timex.h>
  43
  44 .BI "int adjtimex(struct timex *" "buf" );
  45 .fi
  46 .SH DESCRIPTION
  47 Linux uses David L. Mills' clock adjustment algorithm (see RFC\ 1305).
  48 The system call
  49 .BR adjtimex ()
  50 reads and optionally sets adjustment parameters for this algorithm.
  51 It takes a pointer to a
  52 .I timex
  53 structure, updates kernel parameters from field values,
  54 and returns the same structure with current kernel values.
  55 This structure is declared as follows:
  56 .PP
  57 .in +4n
  58 .nf
  59 struct timex {
  60     int  modes;          /* mode selector */
  61     long offset;         /* time offset (usec) */
  62     long freq;           /* frequency offset (scaled ppm) */
  63 .\" FIXME What is the scaling unit of timex.freq?  2^16 ?
  64     long maxerror;       /* maximum error (usec) */
  65     long esterror;       /* estimated error (usec) */
  66     int  status;         /* clock command/status */
  67     long constant;       /* pll time constant */
  68     long precision;      /* clock precision (usec) (read-only) */
  69     long tolerance;      /* clock frequency tolerance (ppm)
  70                             (read-only) */
  71     struct timeval time; /* current time (read-only) */
  72     long tick;           /* usecs between clock ticks */
  73     long ppsfreq;        /* pps frequency (scaled ppm) (read-only) */
  74     long jitter;         /* pps jitter (usec) (read-only) */
  75     int shift;           /* interval duration (sec) (read-only) */
  76     long stabil;         /* pps stability (scaled ppm) (read-only) */
  77     long jitcnt;         /* jitter limit exceeded (read-only) */
  78     long calcnt;         /* calibration intervals (read-only) */
  79     long errcnt;         /* calibration errors (read-only) */
  80     long stbcnt;         /* stability limit exceeded (read-only) */
  81     int tai;             /* TAI offset (sec) (read-only) */
  82 };
  83 .fi
  84 .in
  85 .PP
  86 The
  87 .I modes
  88 field determines which parameters, if any, to set.
  89 It may contain a
  90 .RI bitwise- or
  91 combination of zero or more of the following bits:
  92 .PP
  93 .in +4n
  94 .nf
  95 #define ADJ_OFFSET            0x0001 /* time offset */
  96 #define ADJ_FREQUENCY         0x0002 /* frequency offset */
  97 #define ADJ_MAXERROR          0x0004 /* maximum time error */
  98 #define ADJ_ESTERROR          0x0008 /* estimated time error */
  99 #define ADJ_STATUS            0x0010 /* clock status */
 100 #define ADJ_TIMECONST         0x0020 /* pll time constant */
 101 #define ADJ_TAI               0x0080 /* TAI offset (since Linux 2.6.26) */
 102 #define ADJ_TICK              0x4000 /* tick value */
 103 #define ADJ_OFFSET_SINGLESHOT 0x8001 /* old-fashioned adjtime() */
 104 .fi
 105 .in
 106 .PP
 107 Ordinary users are restricted to a zero value for
 108 .IR modes .
 109 Only the superuser may set any parameters.
 110
 111 In the case of
 112 .BR ADJ_TAI ,
 113 as
 114 .I buf->tai
 115 is read-only, the new value is passed through
 116 .IR buf->constant .
 117 Therefore
 118 .BR ADJ_TAI
 119 should not be used in conjunction with
 120 .BR ADJ_TIMECONST ,
 121 since the latter mode also employs the
 122 .IR buf->constant
 123 field.
 124 .PP
 125 Support for TAI (Atomic International Time)
 126 was added
 127 .\" commit 153b5d054ac2d98ea0d86504884326b6777f683d
 128 in Linux 2.6.26.
 129 For a complete explanation of TAI
 130 and the difference between TAI and UTC, see
 131 .UR http://www.bipm.org/en/bipm/tai/tai.html
 132 .I BIPM
 133 .UE )
 134 .SH RETURN VALUE
 135 On success,
 136 .BR adjtimex ()
 137 returns the clock state:
 138 .PP
 139 .in +4n
 140 .nf
 141 #define TIME_OK   0 /* clock synchronized */
 142 #define TIME_INS  1 /* insert leap second */
 143 #define TIME_DEL  2 /* delete leap second */
 144 #define TIME_OOP  3 /* leap second in progress */
 145 #define TIME_WAIT 4 /* leap second has occurred */
 146 #define TIME_BAD  5 /* clock not synchronized */
 147 .fi
 148 .in
 149 .PP
 150 On failure,
 151 .BR adjtimex ()
 152 returns \-1 and sets
 153 .IR errno .
 154 .SH ERRORS
 155 .TP
 156 .B EFAULT
 157 .I buf
 158 does not point to writable memory.
 159 .TP
 160 .B EINVAL
 161 An attempt is made to set
 162 .I buf.offset
 163 to a value outside the range \-131071 to +131071,
 164 or to set
 165 .I buf.status
 166 to a value other than those listed above,
 167 or to set
 168 .I buf.tick
 169 to a value outside the range
 170 .RB 900000/ HZ
 171 to
 172 .RB 1100000/ HZ ,
 173 where
 174 .B HZ
 175 is the system timer interrupt frequency.
 176 .TP
 177 .B EPERM
 178 .I buf.modes
 179 is nonzero and the caller does not have sufficient privilege.
 180 Under Linux the
 181 .B CAP_SYS_TIME
 182 capability is required.
 183 .SH CONFORMING TO
 184 .BR adjtimex ()
 185 is Linux-specific and should not be used in programs
 186 intended to be portable.
 187 See
 188 .BR adjtime (3)
 189 for a more portable, but less flexible,
 190 method of adjusting the system clock.
 191 .SH SEE ALSO
 192 .BR settimeofday (2),
 193 .BR adjtime (3),
 194 .BR capabilities (7),
 195 .BR time (7),
 196 .BR adjtimex (8)