vCenter Upgrade fails in Stage 2 Pre-upgrade check with the Error: "The source vCenter Server Appliance cannot access the configured NTP servers."

Products

• VMware vCenter Server

Issue/Introduction

Symptoms:
1. vCenter upgrade will fail in stage 2 with the below error:



2. Running the date command shows a visible time difference between the vCenter and the current time on the NTP server.

Cause

This usually happens when the ntpd or the timesyncd service is masked.

Resolution

To resolve this issue we first need to check the status of the ntpd and timesyncd services.

1. Run the below command on the vCenter to check the status:

systemctl status ntpd

Output:
● ntpd.service
   Loaded: masked (Reason: Unit ntpd.service is masked.)
   Active: inactive (dead) 
  Main PID: 1884 (code=exited, status=0/SUCCESS) ...

systemctl status systemd-timesyncd

Output:
● systemd-timesyncd.service
   Loaded: masked (Reason: Unit systemd-timesyncd.service is masked.)
   Active: inactive (dead)

We notice that the ntpd and timesyncd services are masked and currently inactive.

2. Trying to start the ntpd service will give an error, so we need to unmask the service and then start it:

systemctl unmask ntpd
systemctl start ntpd

3. Check the status of the ntpd service and if it shows active, restart the Stage 2 Pre-upgrade check and see if the error is fixed.

systemctl status ntpd

Output:
● ntpd.service - Network Time Service
   Loaded: loaded (/lib/systemd/system/ntpd.service; enabled; vendor preset: disabled)
   Active: active (running) since Sat 2024-02-10 08:25:10 UTC; 5s ago
     Docs: man:ntpd
  Process: 49368 ExecStart=/usr/bin/ntpd -g -u ntp:ntp (code=exited, status=0/SUCCESS)
 Main PID: 49370 (ntpd)
    Tasks: 2 (limit: 9830)
   Memory: 1.5M
   CGroup: /system.slice/ntpd.service
           └─49370 /usr/bin/ntpd -g -u ntp:ntp

Workaround:
If the issue still exists after performing the above steps, unmask the timesyncd service by running the below commands:
systemctl unmask systemd-timesyncd
systemctl start systemd-timesyncd

The Pre-upgrade check should now be completed successfully.

Note: You should not use ntpd and timesyncd in parallel, as in theory, they could pick different time servers that have a slight delay between them. This could result in the vCenter's clock experiencing periodic fluctuations. So, it is recommended to stop (systemctl stop systemd-timesyncd) the timesyncd service after the upgrade is complete.