adjtimex.2: ffix

[thirdparty/man-pages.git] / man2 / adjtimex.2

.\" Copyright (c) 1995 Michael Chastain (mec@shell.portal.com), 15 April 1995.
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.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1997-07-30 by Paul Slootman <paul@wurtel.demon.nl>
.\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.TH ADJTIMEX 2 2014-05-28 "Linux" "Linux Programmer's Manual"
.SH NAME
adjtimex \- tune kernel clock
.SH SYNOPSIS
.nf
.BR "#define _BSD_SOURCE" "      /* See feature_test_macros(7) */"
.B #include <sys/timex.h>

.BI "int adjtimex(struct timex *" "buf" );
.fi
.SH DESCRIPTION
Linux uses David L. Mills' clock adjustment algorithm (see RFC\ 1305).
The system call
.BR adjtimex ()
reads and optionally sets adjustment parameters for this algorithm.
It takes a pointer to a
.I timex
structure, updates kernel parameters from field values,
and returns the same structure with current kernel values.
This structure is declared as follows:
.PP
.in +4n
.nf
struct timex {
    int  modes;          /* Mode selector */
    long offset;         /* Time offset (microseconds) */
    long freq;           /* Frequency offset, as scaled PPM
                            (parts per million) */
.\" FIXME What is the scaling unit of timex.freq?  2^16 ?
    long maxerror;       /* Maximum error (microseconds) */
    long esterror;       /* Estimated error (microseconds) */
    int  status;         /* Clock command/status */
    long constant;       /* PLL (phase-lock loop) time constant */
    long precision;      /* Clock precision (microseconds)
                            (read-only) */
    long tolerance;      /* Clock frequency tolerance (PPM)
                            (read-only) */
    struct timeval time; /* Current time (read-only, except
                            for ADJ_SETOFFSET) */
    long tick;           /* Usecs between clock ticks */
    long ppsfreq;        /* PPS frequency (scaled PPM) (read-only) */
    long jitter;         /* PPS jitter (microseconds)
                            (read-only) */
    int shift;           /* Interval duration (sec) (read-only) */
    long stabil;         /* PPS stability (scaled PPM) (read-only) */
    long jitcnt;         /* Jitter limit exceeded (read-only) */
    long calcnt;         /* Calibration intervals (read-only) */
    long errcnt;         /* Calibration errors (read-only) */
    long stbcnt;         /* Stability limit exceeded (read-only) */
    int tai;             /* TAI offset (sec) (read-only) */
};
.fi
.in
.PP
The
.I modes
field determines which parameters, if any, to set.
It is a bit mask containing a
.RI bitwise- or
combination of zero or more of the following bits:
.TP
.BR ADJ_OFFSET
Time offset.
.TP
.BR ADJ_FREQUENCY
Frequency offset.
.TP
.BR ADJ_MAXERROR
Maximum time error.
.TP
.BR ADJ_ESTERROR
Estimated time error.
.TP
.BR ADJ_STATUS
Clock status.
.TP
.BR ADJ_TIMECONST
PLL time constant.
.TP
.BR ADJ_SETOFFSET " (since Linux 2.6.29)"
.\" commit 094aa1881fdc1b8889b442eb3511b31f3ec2b762
.\" Author: Richard Cochran <richardcochran@gmail.com>
Add
.I buf.time
to the current time.
.TP
.TP
.BR ADJ_MICRO " (since Linux 2.6.36)"
.\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
.\" Author: Roman Zippel <zippel@linux-m68k.org>
Select microsecond resolution.
.TP
.BR ADJ_NANO " (since Linux 2.6.36)"
.\" commit eea83d896e318bda54be2d2770d2c5d6668d11db
.\" Author: Roman Zippel <zippel@linux-m68k.org>
Select nanosecond resolution.
Only one of
.BR ADJ_MICRO
and
.BR ADJ_NANO
should be specified.
.TP
.BR ADJ_TAI " (since Linux 2.6.26)"
TAI offset.
.TP
.BR ADJ_TICK
Tick value.
.TP
.BR ADJ_OFFSET_SINGLESHOT
Old-fashioned
.BR adjtime ().
.PP
Ordinary users are restricted to a zero value for
.IR modes .
Only the superuser may set any parameters.

In the case of
.BR ADJ_TAI ,
as
.I buf->tai
is read-only, the new value is passed through
.IR buf->constant .
Therefore
.BR ADJ_TAI
should not be used in conjunction with
.BR ADJ_TIMECONST ,
since the latter mode also employs the
.IR buf->constant
field.
.PP
Support for TAI (Atomic International Time)
was added
.\" commit 153b5d054ac2d98ea0d86504884326b6777f683d
in Linux 2.6.26.
For a complete explanation of TAI
and the difference between TAI and UTC, see
.UR http://www.bipm.org/en/bipm/tai/tai.html
.I BIPM
.UE )
.SH RETURN VALUE
On success,
.BR adjtimex ()
returns the clock state; that is, one of the following values:
.TP 12
.BR TIME_OK
Clock synchronized.
.TP
.BR TIME_INS
Insert leap second.
.TP
.BR TIME_DEL
Delete leap second.
.TP
.BR TIME_OOP
Leap second in progress.
.TP
.BR TIME_WAIT
Leap second has occurred.
.TP
.BR TIME_BAD
Clock not synchronized.
.PP
On failure,
.BR adjtimex ()
returns \-1 and sets
.IR errno .
.SH ERRORS
.TP
.B EFAULT
.I buf
does not point to writable memory.
.TP
.B EINVAL
An attempt was made to set
.I buf.offset
to a value outside the range \-131071 to +131071,
or to set
.I buf.status
to a value other than those listed above,
or to set
.I buf.tick
to a value outside the range
.RB 900000/ HZ
to
.RB 1100000/ HZ ,
where
.B HZ
is the system timer interrupt frequency.
.TP
.B EPERM
.I buf.modes
is nonzero and the caller does not have sufficient privilege.
Under Linux the
.B CAP_SYS_TIME
capability is required.
.SH CONFORMING TO
.BR adjtimex ()
is Linux-specific and should not be used in programs
intended to be portable.
See
.BR adjtime (3)
for a more portable, but less flexible,
method of adjusting the system clock.
.SH SEE ALSO
.BR settimeofday (2),
.BR adjtime (3),
.BR capabilities (7),
.BR time (7),
.BR adjtimex (8)