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Re: "dmesg -T" date doesn't match "date" output
On Saturday 2018-10-27 19:03 +0700, Robert Elz output:
: Date: Sat, 27 Oct 2018 17:39:16 +1100
: From: Geoff Wing <gcw%pobox.com@localhost>
: Message-ID: <20181027063916.GA2977%primenet.com.au@localhost>
: | dates output by "dmesg -T" are not matching real time. Using a program
: | to generate a segfault dmesg is showing times in the future:
:dmesg times come from "seconds since boot" which is what is actually
:logged, added to boottime. The seconds since boot is, I believe, a monotonic
:counter which counts at timer rate, unadjusted for clock errors.
:I'd assume you're running NTP or similar to sync your clock, and that it
:is constantly slowing down your timer - apparently by 6 seconds since
:boot, which suggests that either your clock is wildly inaccurate, or that
:your system has been up for a fairly lengthy time (at least a week probably).
:What does dmesg say without the -T, or perhaps using -TT
:The dmesg man page should perhaps explain all of this a little better.
I've tried on two -current amd64 machines and both were showing similar issues.
The dmesg time matches what appears in kern.boottime but I don't see a 5-6
second step in rc.log when ntpdate is run. Something fishy is going on.
# ./segfault; date; dmesg -T | tail -1; dmesg -TT | tail -1
 871 segmentation fault ./segfault
Sun Oct 28 09:37:49 AEDT 2018
[Sun Oct 28 09:37:55 AEDT 2018] pid 871 (segfault), uid 0: exited on signal 11 (core not dumped, err = 1)
[PT1M13.006S] pid 871 (segfault), uid 0: exited on signal 11 (core not dumped, err = 1)
# sysctl kern.boottime
kern.boottime = Sun Oct 28 09:36:42 2018
# ntpq -p
remote refid st t when poll reach delay offset jitter
XXXXXXXXXXXX XXXXXXXXXXXXXX 3 s 3 128 7 0.588 -4.308 3.546
XXXXXXXXXXXX XXXXXXXXXXXXXX 3 s 7 128 3 0.228 -3.728 0.066
XXXXXXXXXXXX XXXXXXXXXXXXXX 4 s 62 128 7 0.100 -4.151 2.945
+XXXXXXXXXXXX XXXXXXXXXXXXXX 3 u 28 64 3 0.812 -2.945 2.411
*XXXXXXXXXXXX XXXXXXXXXXXXXX 3 u 80 128 1 12.870 -6.306 0.032
( from /var/run/rc.log )
Setting date via ntp.
28 Oct 09:37:01 ntpdate: step time server XXXXXXXXXXXXXX offset 0.304666 sec
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