Home / server / Questions / 1085737
In Process
Krackout
Asked: 2021-12-09 06:39:12 +0800 CST

Linux guest on Hyper-V host, realtime clock, UTC or local - sync with AD DC

  • 772

I'm installing a Debian 11 Linux guest on a Hyper-V cluster. Hosts' realtime clocks are set to local time, as is the norm for Windows Servers; unlike the preference of Unix-like OSes. Should I execute timedatectl set-local-rtc 1 on the Linux guest, to be in line with its hosts?

Setting real time clock to local time on Linux systemd servers reports this:

Warning: The system is configured to read the RTC time in the local time zone.
     This mode can not be fully supported. It will create various problems
     with time zone changes and daylight saving time adjustments. The RTC
     time is never updated, it relies on external facilities to maintain it.

If time is synced with an NTP source or from the hypervisor, will there be any potential problems? That's the first part of my question.

Second part,

  • Can systemd timesyncd or ntpd sync time with a Windows AD time server (the DC holding the PDC emulator role)? My initial attempt failed for both services. Of course sync time with host was unchecked on VM's settings.
  • As an alternative, is syncing time from HyperV host (which in turn is in sync with AD DC) trustworthy?
linux hyper-v guest ntpd systemd-timesyncd

1 Answers

  1. timedatectl set-local-rtc 0

    Set RTC to UTC. Per that warning, the annoyance of local RTC is not worth it when the clock can actually be managed with other means.

    pool ad.example.net
# Optional PTP config for chrony
#refclock PHC /dev/ptp0 poll 3 dpoll -2 offset 0

    AD DS runs a NTP service on all DCs by default. Set ntp.conf or chrony.conf to the domain name. Hyper-V also makes available a PTP "hardware" clock to share the hosts time with very low latency.

    Confirm Hyper-V hosts have the correct time. Probably they should be domain members and follow the domain in this regard.

    Ensure Hyper-V guest integration is installed. May be already, I'm not positive what Debian kernels are doing. hv_vmbus driver is sufficient to allow Time Synchronization.

    You may use NTP, Hyper-V time sync, or both.

    • 0