I have a small cluster at home for testing with three nodes. On two of them, I was able to change the Proxmox host boot kernel without any problems, very easily using the Proxmox tools, but on one of them there is no way, and as always, it is the one I need. What is special about this machine is that I applied the Proxmox xshok script to it at the time, and no matter how hard I try, there is no way.