[opensuse-virtual] sistemad telling me "Time has been changed", only on xen guests?
After having migrated a number of systems to a xen setup, I am seeing this "Time has been changed" message from systemd twice a minute in the guest systems (once per systemd daemon). The host is running ntpd, the guests aren't. Both host and guests are using openSUSE 13.2 + latest updates. I guess it's not causing any problems, but I'd like to understand what it means. -- Per Jessen, Zürich (5.2°C) http://www.hostsuisse.com/ - virtual servers, made in Switzerland. -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
Per Jessen wrote:
After having migrated a number of systems to a xen setup, I am seeing this "Time has been changed" message from systemd twice a minute in the guest systems (once per systemd daemon). The host is running ntpd, the guests aren't. Both host and guests are using openSUSE 13.2 + latest updates.
I guess it's not causing any problems, but I'd like to understand what it means.
Having done some more research, it seems to be due to my not running ntpd on the guests. Is it possible to have a guest ntpd sync'ing directly to the dom0 clock, i.e. without causing any network traffic? -- Per Jessen, Zürich (9.3°C) http://www.hostsuisse.com/ - dedicated server rental in Switzerland. -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
Hi,
Somewhere there is an article about the evils of syncing to your
system clock, or at least doing it in a very specific way.
Unless you run an ntpd on your HostOS, you can't run an ntp client
pointing to your Host.'
The proper way to implement is to point all your machines (both HostOS
and Guests) to some highly available network ntpd.
For those running network security, this might be a Domain Controller.
For most others, this probably would mean pointing to a ntpd on the Internet.
Tony
On Mon, Mar 16, 2015 at 4:16 AM, Per Jessen
Per Jessen wrote:
After having migrated a number of systems to a xen setup, I am seeing this "Time has been changed" message from systemd twice a minute in the guest systems (once per systemd daemon). The host is running ntpd, the guests aren't. Both host and guests are using openSUSE 13.2 + latest updates.
I guess it's not causing any problems, but I'd like to understand what it means.
Having done some more research, it seems to be due to my not running ntpd on the guests. Is it possible to have a guest ntpd sync'ing directly to the dom0 clock, i.e. without causing any network traffic?
-- Per Jessen, Zürich (9.3°C) http://www.hostsuisse.com/ - dedicated server rental in Switzerland.
-- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
-- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
Tony Su wrote:
Hi, Somewhere there is an article about the evils of syncing to your system clock, or at least doing it in a very specific way.
Hi Tony yes, there is a lot of articles out there, and they don't all agree :-(
Unless you run an ntpd on your HostOS,
The xen host is sync'ed to our local time source.
you can't run an ntp client pointing to your Host.'
Right.
The proper way to implement is to point all your machines (both HostOS and Guests) to some highly available network ntpd.
Okay - is this the way everybody does it here? -- Per Jessen, Zürich (9.7°C) http://www.hostsuisse.com/ - dedicated server rental in Switzerland. -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
On Mon, Mar 16, Per Jessen wrote:
After having migrated a number of systems to a xen setup, I am seeing this "Time has been changed" message from systemd twice a minute in the guest systems (once per systemd daemon). The host is running ntpd, the guests aren't. Both host and guests are using openSUSE 13.2 + latest updates.
I remember such systemd output, looks like a bug in that component. I dont know much about time keeping. My understanding is that Xen does a reasonable good job of keeping dom0 and domU time in sync. I think the only requirement or recommendation is that dom0 runs ntpd. There is some knob to make a domU not use dom0 time, not sure if you have that enabled for your domUs. But such knob may only apply to PV guests. Olaf -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
Olaf Hering wrote:
On Mon, Mar 16, Per Jessen wrote:
After having migrated a number of systems to a xen setup, I am seeing this "Time has been changed" message from systemd twice a minute in the guest systems (once per systemd daemon). The host is running ntpd, the guests aren't. Both host and guests are using openSUSE 13.2 + latest updates.
I remember such systemd output, looks like a bug in that component.
I dont know much about time keeping. My understanding is that Xen does a reasonable good job of keeping dom0 and domU time in sync. I think the only requirement or recommendation is that dom0 runs ntpd.
That's what I thought too. With that setup, I get $SUBJ though.
There is some knob to make a domU not use dom0 time, not sure if you have that enabled for your domUs. But such knob may only apply to PV guests.
For the time being (no pun intended), I've set xen.independent_wallclock=1 on my guests and started ntpd on them too. What do other people here do? I can't help thinking ntp might/could have an option for sync'ing to the dom0, maybe a special server a la : server 127.127.1.0 # local clock (LCL) -- Per Jessen, Zürich (8.4°C) http://www.hostsuisse.com/ - dedicated server rental in Switzerland. -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
Olaf Hering wrote:
On Mon, Mar 16, Per Jessen wrote:
After having migrated a number of systems to a xen setup, I am seeing this "Time has been changed" message from systemd twice a minute in the guest systems (once per systemd daemon). The host is running ntpd, the guests aren't. Both host and guests are using openSUSE 13.2 + latest updates.
I remember such systemd output, looks like a bug in that component.
I dont know much about time keeping. My understanding is that Xen does a reasonable good job of keeping dom0 and domU time in sync. I think the only requirement or recommendation is that dom0 runs ntpd.
I have problem with domU clock. It lose 30 minutes each day. How can i synchronize it with dom0 clock?
Is this PV domU? If yes, setting /proc/sys/xen/independent_wallclock to 0 (the default) should make it sync with dom0. You only need ntp on dom0, and domUs will follow.
This is the setup I started out with, and where I see systemd reporting "Time has been changed" about once a minute. OTOH, that same paragraph also says:
The alternative, set /proc/sys/xen/independent_wallclock to 1 and run ntp on domU.
Which is what I am doing now. No systemd messages. Most confusing, to be honest. -- Per Jessen, Zürich (8.6°C) http://www.dns24.ch/ - your free DNS host, made in Switzerland. -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
Per Jessen [19.03.2015 09:07]:
I have problem with domU clock. It lose 30 minutes each day. How can i synchronize it with dom0 clock?
Is this PV domU? If yes, setting /proc/sys/xen/independent_wallclock to 0 (the default) should make it sync with dom0. You only need ntp on dom0, and domUs will follow.
This is the setup I started out with, and where I see systemd reporting "Time has been changed" about once a minute.
OTOH, that same paragraph also says:
The alternative, set /proc/sys/xen/independent_wallclock to 1 and run ntp on domU.
Which is what I am doing now. No systemd messages.
Most confusing, to be honest.
When you install SAP systems on top of Xenified VMs, there is the recommendation to do the latter: disable the sync and run a separate ntpd in the DomU. This is also a recommendation for VMs inside a VMWare environment - the problem ist the same there. It did not cause pain to set up one host as ntp server with "outer world" sources and the VMs as ntp clients listening to that host only, so I do not get headache while pondering which way to sync time :) Just my 2¢, Werner --
participants (4)
-
Olaf Hering -
Per Jessen -
Tony Su -
Werner Flamme