Automatically set the RTC

[yaxattax]

Hi all,

I've got Fedora 16 on a laptop - I've read that Linux purposefully doesn't set the RTC because of some dualbooting setups. The problem is that because of this, when I am not connected to the network (I enabled network time syncing during setup), during summer time the clock is incorrect. How do I enable the setting of the RTC by linux in order that I do not have this issue?

Kind regards,

Yax

[Gareth Jones]

EDIT: I think I may have misunderstood your question! As for how to save the time on shutdown, I'll have a look, but I'm not familiar with the new systemd way of doing things.

For my attempt at an explanation of the relationship between Linux and the hardware clock, see http://forums.fedoraforum.org/showpo...41&postcount=8.

To change the settings, run system-config-date. Make sure that your hardware clock is set correctly too – i.e. if "System clock uses UTC" is checked, as is best unless you dual-boot with Windows, then the BIOS clock must be set to UTC, otherwise set it to local time. You might want to enable network time too.

[yaxattax]

Actually, although you misunderstood, your comments were useful. I'd read somewhere that the NTP Daemon sets the RTC, but I somewhat glossed over it - when you mentioned network time I checked to see if my system was running ntpd. Nope.

Checked with systemctl --all, and it had errored / not loaded. ntpd is not installed - i don't know how my system time was being updated when I had a network connection, but it was. yum install ntp fixed the issue and now my system time is correct regardless of whether I have a network connection or not.

Cheers for the help.

Yax

[Gareth Jones]

I think F16 switched from NTPD to Chrony as the default network time client. I'm not sure of the rationale, or whether switching back to NTPD is likely to cause problems; just something to beware of by way of explanation.

[marko]

chrony is a bit better at dealing with sporadic network connections. ntp has a maximum error limit of 1000 secs, if the RTC was off more than that, ntpd gives up and exit. The way past that was to use
the ntpd -g option or ntpdate like mentioned below. I'm not sure if chrony has a default max limit, I don't see mention of it in the man page.

I think Fedora 16 uses ntpdate.service to do a 'one shot' setting of the clock at boot up. That's to take care of the clock being wildly off like months/days/hours (maybe you replaced the bios battery so the clock is way off)
then chronyd.service runs and keeps it accurate.

[yaxattax]

Well chronyd was not updating the RTC, only the system time, so whenever I booted up without a network connection, I saw the time as if summer time had not been applied.

I'll have a look to see if I can get chrony to update the RTC.

[marko]

Maybe you make sure you've got the ntpdate.service activated via systemctl and then go in /etc/sysconfig/ntpdate and set SYNC_HWCLOCK to yes like this (quoting the file ):

# Set to 'yes' to sync hw clock after successful ntpdate
SYNC_HWCLOCK=yes

I have SYNC_HWCLOCK set "no" but the command

hwclock --show

shows my RTC clock is set, so I'm not sure why mine is updated, I do have the time-sync.target so maybe that does it?

See also this BUG -- https://bugzilla.redhat.com/show_bug.cgi?id=753487

[stevea]

Originally Posted by marko

chrony is a bit better at dealing with sporadic network connections. ntp has a maximum error limit of 1000 secs, if the RTC was off more than that, ntpd gives up and exit.

The ntp protocol is quite complex, but yes if the ntp derived time (after sync'ing with multiple (3 min) servers) duesn't match the system time (aka kernel time) within 1000 seconds, then ntp refuses to set the HWclock (which is not the system clock). So the 1000 second error from system time requires manual intervetion but this prevents setting the hwclock with a grossly bad time without human intervention - that's very reasonably behavior.

It does not just quit or exit. For any amount of error between ntp time and system time - then ntp slowly drifts to clock toward the correct value. ntp also keeps statisticis about the variability of it's own time estimates based on ntp server data and estimates of packet delay - then then it ceases to tweak the system time very much when the system time matches 'within the noise'.

Originally Posted by marko

Maybe you make sure you've got the ntpdate.service activated via systemctl and then go in /etc/sysconfig/ntpdate and set SYNC_HWCLOCK to yes like this (quoting the file ):
SYNC_HWCLOCK=yes

DO NOT do that if you use chrony. the documentation makes clear that chrony leaves a setting and drift file behind and it uses that at boot to correct system time from the hwclock value. detail here ...
http://chrony.tuxfamily.org/FAQ.html#question_9.1

Also note that in F16 that chrony is setup to set the hwclock every 11 minutes by default.
See the rtcsync parameter
/usr/share/doc/chrony-1.26/chrony.txt

In /etc/chrony.conf we have

# Enable kernel RTC synchronization.
rtcsync

The documentation is ....

The `rtcsync' directive will enable a kernel mode where the system time
is copied to the real time clock (RTC) every 11 minutes.

This directive is supported only on Linux and cannot be used when the
normal RTC tracking is enabled, i.e. when the `rtcfile' directive is
used.

Originally Posted by yaxattax

Hi all,

I've got Fedora 16 on a laptop - I've read that Linux purposefully doesn't set the RTC because of some dualbooting setups.

That's not quite true. Sometime ther is an option to NOT set the HWclock (usually outsude of chrony/ntp) , but the default a have generally been to set it. F16 does not reset the rtc(hwclock) in scripts but does set it from chrony.

The problem is that because of this, when I am not connected to the network (I enabled network time syncing during setup), during summer time the clock is incorrect. How do I enable the setting of the RTC by linux in order that I do not have this issue?

Why only summer ? Is the error close to 1 hour - as in failure to set daylight saving time ?

i suggest you post the output of .....

[root@lycoperdon stevea]# date ; date -u; TZ=0 hwclock 
Wed Apr 11 23:26:53 EDT 2012
Thu Apr 12 03:26:53 UTC 2012
Thu 12 Apr 2012 03:26:54 AM   -0.219197 seconds

Then verify the local time and UTC times are correct. Compare to ....
http://www.time.gov/timezone.cgi?UTC/s/0/java


==========

Well chronyd was not updating the RTC, only the system time, so whenever I booted up without a network connection, I saw the time as if summer time had not been applied.

That sort of one-hour error has to do with an incorrect Time-zone setting (and maybe a correcsponding RTC setting error) and not a problem with chrony or system time.

The time zone value is in /etc/adjtime and you should only edit that file using the clock utility on the top panel clock - click it, select edit .. and find some place in your TZ.

[Doug G]

On a recent fresh un-tweaked f16 dvd install ntp & ntpdate aren't even installed.

I think Fedora 16 uses ntpdate.service to do a 'one shot' setting of the clock at boot up. That's to take care of the clock being wildly off like months/days/hours (maybe you replaced the bios battery so the clock is way off)

[yaxattax]

[root@yaxattax-vse:~]$ date ; date -u; TZ=0 hwclock
Thu Apr 12 08:12:05 BST 2012
Thu Apr 12 07:12:05 UTC 2012
Thu 12 Apr 2012 07:12:06 AM   -0.532218 seconds
[root@yaxattax-vse:~]$

[root@yaxattax-vse:~]$ cat /etc/adjtime 
0.004817 1334214476 0.000000
1334214476
UTC
[root@yaxattax-vse:~]$

Why only summer ? Is the error close to 1 hour - as in failure to set daylight saving time ?

The error was one hour. The problem is not reproducible now - after I set

systemctl enable ntpd.service

and rebooted the system, even now when I have disabled the ntp daemon, I no longer observe the issue where the system time is incorrect when I have no network connection after a reboot.

My TZ settings were correct - I had "System clock uses UTC" and my TZ set as London. Do you have any idea as to why Summer time was not being correctly applied before I used the ntpd?