Update hwclock man page for the hwclock: hctosys drift compensation II patch. Signed-off-by: J William Piggott <elseifthen@xxxxxxx> --- sys-utils/hwclock.8.in | 50 +++++++++++++++++++++++++++++++++----------------- 1 file changed, 33 insertions(+), 17 deletions(-) diff --git a/sys-utils/hwclock.8.in b/sys-utils/hwclock.8.in index b11b45c..913da37 100644 --- a/sys-utils/hwclock.8.in +++ b/sys-utils/hwclock.8.in @@ -61,8 +61,18 @@ in Coordinated Universal Time. See the option. Showing the Hardware Clock time is the default when no function is specified. .TP +.B \-\-get +Like +.B --show +only with drift correction applied to the time read. This is useful when the +Hardware Clock is not being periodically updated by something such as NTP's +11 minute mode or when not using +.BR --adjust . +.TP .BR \-s , \ \-\-hctosys -Set the System Time from the Hardware Clock. +Set the System Time from the Hardware Clock. The time read from the Hardware +Clock is compensated to account for systematic drift before using it to set the +System Clock. See the discussion below, under \fBThe Adjust Function\fR. .PP Also set the kernel's timezone value to the local timezone as indicated by the TZ environment variable and/or @@ -484,8 +494,9 @@ The Hardware Clock is usually not very accurate. However, much of its inaccuracy is completely predictable - it gains or loses the same amount of time every day. This is called systematic drift. .BR hwclock 's -"adjust" function lets you make systematic corrections to correct the -systematic drift. +.I \-\-adjust +function lets you apply systematic drift corrections to the +Hardware Clock. .PP It works like this: .B hwclock @@ -529,20 +540,25 @@ since the last calibration, how long it has been since the last adjustment, what drift rate was assumed in any intervening adjustments, and the amount by which the clock is presently off. .PP -A small amount of error creeps in any time -.B hwclock -sets the clock, so it refrains from making an adjustment that would be -less than 1 second. Later on, when you request an adjustment again, -the accumulated drift will be more than a second and -.B hwclock -will do the adjustment then. -.PP -It is good to do a -.I hwclock \-\-adjust -just before the -.I hwclock \-\-hctosys -at system startup time, and maybe periodically while the system is -running via cron. +A small amount of error creeps in when +the Hardware Clock is set, so +.I \-\-adjust +refrains from making any adjustment that is less +than 1 second. Later on, when you request an adjustment again, the accumulated +drift will be more than 1 second and +.I \-\-adjust +will make the adjustment including any fractional amount. +.PP +.IR "hwclock \-\-hctosys" +also uses the adjtime file data to compensate the value read from the Hardware +Clock before using it to set the System Time. It does not share the 1 second +limitation of --adjust, and will correct sub-second drift values immediately. +It does not change the Hardware Clock time or the adjtime file. This may +eliminate the need to use --adjust, unless something else on the system needs +the Hardware Clock to be compensated. The drift compensation can be inhibited +by using the +.B --noadjfile +option. .PP The adjtime file, while named for its historical purpose of controlling adjustments only, actually contains other information for use by hwclock -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
