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hwclock: update man page 

Add information about setting the Hardware Clock if it has been
corrupted.

Add information about --update-drift and reduced system shutdown
times for --systohc.

Signed-off-by: J William Piggott <elseifthen@gmx.com>
This commit is contained in:
J William Piggott 2017-07-30 21:28:36 -04:00
parent 1ef6feb533
commit fefc39f965
1 changed files with 20 additions and 6 deletions
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26
sys-utils/hwclock.8.in
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@ -4,7 +4,7 @@
.\" Authored new section: DATE-TIME CONFIGURATION.
.\" Subsections: Keeping Time..., LOCAL vs UTC, POSIX vs 'RIGHT'.
.\"
.TH HWCLOCK 8 "April 2015" "util-linux" "System Administration"
.TH HWCLOCK 8 "July 2017" "util-linux" "System Administration"
.SH NAME
hwclock \- time clocks utility
.SH SYNOPSIS
@ -197,8 +197,9 @@ Set the Hardware Clock to the time given by the
option, and update the timestamps in
.IR @ADJTIME_PATH@ .
With the
.B --update-drift
option (re)calculate the drift factor.
.B \%\-\-update-drift
option also (re)calculate the drift factor. Try it without the option if
.BR \%\-\-set " fails. See " \%\-\-update-drift " below."
.
.TP
.B \-\-systz
@ -234,9 +235,10 @@ changed then a reboot would be required to inform the kernel.
.BR \-w , \ \-\-systohc
Set the Hardware Clock from the System Clock, and update the timestamps in
.IR @ADJTIME_PATH@ .
When the
.B --update-drift
option is given, then also (re)calculate the drift factor.
With the
.B \%\-\-update-drift
option also (re)calculate the drift factor. Try it without the option if
.BR \%\-\-systohc " fails. See " \%\-\-update-drift " below."
.
.TP
.BR \-V , \ \-\-version
@ -404,6 +406,11 @@ on the drift factor.
(Re)calculating drift factor on every shutdown delivers suboptimal
results. For example, if ephemeral conditions cause the machine to be
abnormally hot the drift factor calculation would be out of range.
.IP \(bu 2
Significantly increased system shutdown times (as of v2.31 when not
using
.B \%\-\-update\-drift
the RTC is not read).
.PP
.RB "Having " \%hwclock
calculate the drift factor is a good starting point, but for optimal
@ -414,6 +421,13 @@ crafted it should not need to be changed. Therefore, the old behavior to
automatically (re)calculate drift was changed and now requires this
option to be used. See the discussion below, under
.BR "The Adjust Function" .
.PP
This option requires reading the Hardware Clock before setting it. If
it cannot be read, then this option will cause the set functions to fail.
This can happen, for example, if the Hardware Clock is corrupted by a
power failure. In that case, the clock must first be set without this
option. Despite it not working, the resulting drift correction factor
would be invalid anyway.
.RE
.
.SH NOTES