When we process, it shows :
With this issue, system processes to get a subscription repo without purchase subscription on this server. So it shows an error message for notice unable to get repo source. For fixing this problem you should
1. Remove the subscription repo that had set in source list.
2. Add a no subscription repo for free in Proxmox system.
Add Non-Subscription Repo of Proxmox Enterprise
Access apt list of enterprise repo in Proxmox server by web CLI or SSH. This directory store all the apt source list.
cp pve-enterprise.list pve-no-subscription.list
Open the copy file.
Replace this file with the no subscription URL, ctrl+x and YES to save
deb http://download.proxmox.com/debian/pve stretch pve-no-subscription
At last, run:
The error still there, but now you can update Proxmox as no subscription.
Tips: Always run dist-upgrade, not just “apt-get upgrade.”
Dist-upgrade ensures that all packages and their dependencies are updated; if you just run “apt-get upgrade” things may break.