In brief:
Early 2017: Installed PVE ontop a Debian 8.x according to https://pve.proxmox.com/wiki/Install_Proxmox_VE_on_Debian_Jessie
Late 2017: Upgraded Debian to version 9 Stretch
Early 2018: Ran update for Meltdown/Spectre in week 2
week 3: /boot reportedly nearly out of free space
Ran...
