I have read multiple times (although I can't find it right now) that data centers take great effort to make sure that all server have the exact same time. Including, but not limited to worrying about leap seconds.
Why is it so important that servers have the same time? And what are the actual tolerances?
I have CentOS machine and each time I've noticed that the server loses correct time after a while. It is usually behind by several minutes after time passes from having manually set the correct time. Is there a mechanism whereby I can update the server with the time from a specific time server?
On my host I am using libvirt and a KVM guest. When the host is shutting down, libvirt suspends the guest. When the host is starting up, libvirt resumes the guest. The problem is, if the guest is suspended and resumed after 24 hours for example, then the guest time is 24 hours in the past.
I thought that maybe the problem is with the clocksource, but it is set to "kvm-clock" already.
$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
kvm-clock tsc hpet acpi_pm
$ cat /sys/devices/system/clocksource/clocksource0/current_clocksource
kvm-clock
I've come across a handful of GPS NTP servers, as well as some inexpensive solutions using off-the-shelf receivers and software. Right now I'm just using NTP with a list of servers over the Internet. What is the advantage to using GPS instead (considering the alternative is free)?
Why does Windows Server (2008, in this case, but I've seen the same problem in 2003) seem to have problem synchronizing time? I've seen this error in my System log across a variety of servers:
The time service has not synchronized the system time for 86400 seconds because none of the time service providers provided a usable time stamp. The time service will not update the local system time until it is able to synchronize with a time source. If the local system is configured to act as a time server for clients, it will stop advertising as a time source to clients. The time service will continue to retry and sync time with its time sources. Check system event log for other W32time events for more details. Run 'w32tm /resync' to force an instant time synchronization.
Under Control Panel, Date and Time, The Internet Time Settings are set to synchronize with time-nw.nist.gov ; the last successful sync was 2 days ago, indicating there's some kind of problem. But if I click the "update now" button on that dialog, indeed, it updates with the time!
So why can't windows server reliably time sync via NTP in the background without me manually intervening? What am I doing wrong?