man2/adjtimex.2

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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>
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  29 .TH ADJTIMEX 2 2004-05-27 "Linux" "Linux Programmer's Manual"
  30 .SH NAME
  31 adjtimex \- tune kernel clock
  32 .SH SYNOPSIS
  33 .B #include <sys/timex.h>
  34 .sp
  35 .BI "int adjtimex(struct timex *" "buf" );
  36 .SH DESCRIPTION
  37 Linux uses David L. Mills' clock adjustment algorithm (see RFC\ 1305).
  38 The system call
  39 .BR adjtimex ()
  40 reads and optionally sets adjustment parameters for this algorithm.
  41 It takes a pointer to a
  42 .I timex
  43 structure, updates kernel parameters from field values,
  44 and returns the same structure with current kernel values.
  45 This structure is declared as follows:
  46 .PP
  47 .in +4n
  48 .nf
  49 struct timex {
  50     int modes;           /* mode selector */
  51     long offset;         /* time offset (usec) */
  52     long freq;           /* frequency offset (scaled ppm) */
  53 .\" FIXME -- what is the scaling unit?  2^16 ?
  54     long maxerror;       /* maximum error (usec) */
  55     long esterror;       /* estimated error (usec) */
  56     int status;          /* clock command/status */
  57     long constant;       /* pll time constant */
  58     long precision;      /* clock precision (usec) (read-only) */
  59     long tolerance;      /* clock frequency tolerance (ppm)
  60                             (read-only) */
  61     struct timeval time; /* current time (read-only) */
  62     long tick;           /* usecs between clock ticks */
  63 };
  64 .fi
  65 .in
  66 .PP
  67 The
  68 .I modes
  69 field determines which parameters, if any, to set.
  70 It may contain a
  71 .RI bitwise- or
  72 combination of zero or more of the following bits:
  73 .PP
  74 .in +4n
  75 .nf
  76 #define ADJ_OFFSET            0x0001 /* time offset */
  77 #define ADJ_FREQUENCY         0x0002 /* frequency offset */
  78 #define ADJ_MAXERROR          0x0004 /* maximum time error */
  79 #define ADJ_ESTERROR          0x0008 /* estimated time error */
  80 #define ADJ_STATUS            0x0010 /* clock status */
  81 #define ADJ_TIMECONST         0x0020 /* pll time constant */
  82 #define ADJ_TICK              0x4000 /* tick value */
  83 #define ADJ_OFFSET_SINGLESHOT 0x8001 /* old-fashioned adjtime() */
  84 .fi
  85 .in
  86 .PP
  87 Ordinary users are restricted to a zero value for
  88 .IR mode .
  89 Only the superuser may set any parameters.
  90 .br
  91 .ne 12v
  92 .SH "RETURN VALUE"
  93 On success,
  94 .BR adjtimex ()
  95 returns the clock state:
  96 .PP
  97 .in +4n
  98 .nf
  99 #define TIME_OK   0 /* clock synchronized */
 100 #define TIME_INS  1 /* insert leap second */
 101 #define TIME_DEL  2 /* delete leap second */
 102 #define TIME_OOP  3 /* leap second in progress */
 103 #define TIME_WAIT 4 /* leap second has occurred */
 104 #define TIME_BAD  5 /* clock not synchronized */
 105 .fi
 106 .in
 107 .PP
 108 On failure,
 109 .BR adjtimex ()
 110 returns \-1 and sets
 111 .IR errno .
 112 .SH ERRORS
 113 .TP
 114 .B EFAULT
 115 .I buf
 116 does not point to writable memory.
 117 .TP
 118 .B EINVAL
 119 An attempt is made to set
 120 .I buf.offset
 121 to a value outside the range \-131071 to +131071,
 122 or to set
 123 .I buf.status
 124 to a value other than those listed above,
 125 or to set
 126 .I buf.tick
 127 to a value outside the range
 128 .RB 900000/ HZ
 129 to
 130 .RB 1100000/ HZ ,
 131 where
 132 .B HZ
 133 is the system timer interrupt frequency.
 134 .TP
 135 .B EPERM
 136 .I buf.mode
 137 is nonzero and the caller does not have sufficient privilege.
 138 Under Linux the
 139 .B CAP_SYS_TIME
 140 capability is required.
 141 .SH "CONFORMING TO"
 142 .BR adjtimex ()
 143 is Linux-specific and should not be used in programs
 144 intended to be portable.
 145 See
 146 .BR adjtime (3)
 147 for a more portable, but less flexible,
 148 method of adjusting the system clock.
 149 .SH "SEE ALSO"
 150 .BR settimeofday (2),
 151 .BR adjtime (3),
 152 .BR capabilities (7),
 153 .BR time (7)