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1 | .TH ADJTIME_CONFIG 5 "August 2018" "util-linux" "File Formats" |
2 | .SH NAME | |
3 | adjtime \- information about hardware clock setting and drift factor | |
4 | .SH SYNOPSIS | |
5 | .I /etc/adjtime | |
6 | .SH DESCRIPTION | |
7 | The file | |
8 | .B /etc/adjtime | |
9 | contains descriptive information about the hardware mode clock setting and clock drift factor. | |
10 | The file is read and write by hwclock; and read by programs like rtcwake to get RTC time mode. | |
11 | .PP | |
12 | The file is usually located in /etc, but tools like | |
13 | .BR hwclock (8) | |
14 | or | |
15 | .BR rtcwake (8) | |
16 | allow to use alternative location by command line options if write access to | |
17 | /etc is unwanted. The default clock mode is "UTC" if the file is missing. | |
18 | .PP | |
2bb3aa36 | 19 | The Hardware Clock is usually not very accurate. However, much of its inaccuracy is completely predictable - it gains |
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20 | or loses the same amount of time every day. This is called systematic drift. The util hwclock keeps the file /etc/adjtime, |
21 | that keeps some historical information. | |
22 | For more details see "\fBThe Adjust Function\fR" and "\fBThe Adjtime File\fR" sections from | |
dbeb1d73 | 23 | .BR hwclock (8) |
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24 | man page. |
25 | .PP | |
26 | ||
27 | The format of the adjtime file is, in ASCII. | |
28 | .sp | |
29 | .SS First line | |
30 | Three numbers, separated by blanks: | |
31 | .TP | |
32 | .B "drift factor" | |
33 | the systematic drift rate in seconds per day (floating point decimal) | |
34 | .TP | |
35 | .B last adjust time | |
36 | the resulting number of seconds since 1969 UTC of most recent adjustment or calibration (decimal integer) | |
37 | .TP | |
38 | .B "adjustment status" | |
39 | zero (for compatibility with clock(8)) as a decimal integer. | |
40 | ||
41 | .SS Second line | |
42 | .TP | |
43 | .B "last calibration time" | |
44 | The resulting number of seconds since 1969 UTC of most recent calibration. | |
45 | Zero if there has been no calibration yet or it is known that any previous | |
46 | calibration is moot (for example, because the Hardware Clock has been found, | |
47 | since that calibration, not to contain a valid time). This is a decimal | |
48 | integer. | |
49 | ||
50 | .SS Third line | |
51 | .TP | |
52 | .B "clock mode" | |
53 | Supported values are "UTC" or "LOCAL". Tells whether the Hardware Clock is set | |
54 | to Coordinated Universal Time or local time. You can always override this | |
55 | value with options on the hwclock command line. | |
56 | ||
57 | .SH FILES | |
58 | .IR /etc/adjtime | |
59 | .SH "SEE ALSO" | |
60 | .BR hwclock (8), | |
61 | .BR rtcwake (8) | |
62 | .SH AVAILABILITY | |
63 | This man page is part of the util-linux package and is available from | |
64 | https://www.kernel.org/pub/linux/utils/util-linux/. |