When you’re using Proxmox for free without any subscription you may see


TASK ERROR: command 'apt-get update' failed: exit code 100
The issue here is that by default Proxmox is using subscription only repos, you can remove this “error” by either getting a subscription (duh), or change the repo to pve-no-subscription. This repo is not as stable as the subscription one they claim, but for a home server it should be enough. If you really need the stability you’re probably running a critial environment which probably is worth paying for the subscription.

To change the repo edit your /etc/apt/sources.list and set the repo to pve-no-subscription.


deb http://ftp.debian.org/debian buster main contrib
deb http://ftp.debian.org/debian buster-updates main contrib

# PVE pve-no-subscription repository provided by proxmox.com,
# NOT recommended for production use
deb http://download.proxmox.com/debian/pve buster pve-no-subscription

# security updates
deb http://security.debian.org/debian-security buster/updates main contrib

Source: https://pve.proxmox.com/wiki/Package_Repositories#sysadmin_no_subscription_repo