65 lines
2.2 KiB
Groff
65 lines
2.2 KiB
Groff
.TH ADJTIME_CONFIG 5 "August 2018" "util-linux" "File Formats"
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.SH NAME
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adjtime \- information about hardware clock setting and drift factor
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.SH SYNOPSIS
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.I /etc/adjtime
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.SH DESCRIPTION
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The file
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.B /etc/adjtime
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contains descriptive information about the hardware mode clock setting and clock drift factor.
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The file is read and write by hwclock; and read by programs like rtcwake to get RTC time mode.
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.PP
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The file is usually located in /etc, but tools like
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.BR hwclock (8)
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or
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.BR rtcwake (8)
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allow to use alternative location by command line options if write access to
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/etc is unwanted. The default clock mode is "UTC" if the file is missing.
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.PP
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The Hardware Clock is usually not very accurate. However, much of its inaccuracy is completely predictable - it gains
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or loses the same amount of time every day. This is called systematic drift. The util hwclock keeps the file /etc/adjtime,
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that keeps some historical information.
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For more details see "\fBThe Adjust Function\fR" and "\fBThe Adjtime File\fR" sections from
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.BR hwclock (8)
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man page.
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.PP
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The format of the adjtime file is, in ASCII.
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.sp
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.SS First line
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Three numbers, separated by blanks:
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.TP
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.B "drift factor"
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the systematic drift rate in seconds per day (floating point decimal)
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.TP
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.B last adjust time
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the resulting number of seconds since 1969 UTC of most recent adjustment or calibration (decimal integer)
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.TP
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.B "adjustment status"
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zero (for compatibility with clock(8)) as a floating point decimal
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.SS Second line
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.TP
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.B "last calibration time"
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The resulting number of seconds since 1969 UTC of most recent calibration.
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Zero if there has been no calibration yet or it is known that any previous
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calibration is moot (for example, because the Hardware Clock has been found,
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since that calibration, not to contain a valid time). This is a decimal
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integer.
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.SS Third line
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.TP
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.B "clock mode"
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Supported values are "UTC" or "LOCAL". Tells whether the Hardware Clock is set
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to Coordinated Universal Time or local time. You can always override this
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value with options on the hwclock command line.
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.SH FILES
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.IR /etc/adjtime
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.SH "SEE ALSO"
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.BR hwclock (8),
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.BR rtcwake (8)
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.SH AVAILABILITY
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This man page is part of the util-linux package and is available from
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https://www.kernel.org/pub/linux/utils/util-linux/.
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