Changing the host name of a Proxmox node is unfortunately a bit harder than changing the hostname of your typical Linux machine. This article will guide you through the process. Keep in mind that this only covers changing the host name for a standalone node, I don’t know if the process is different when the node is part of a cluster.
If you are running a Linux server that don’t have rebootless kernel patching like KernelCare or Canonical Livepatch then chances are you are running an out of date kernel. And that is understandable because keep tracking of new kernels and rebooting your servers isn’t fun. But Nagios can do that job for you, or at least the part of looking for a new kernel, and then notify you of when it’s time to reboot! That way you don’t have to worry about being vulnerable to known kernel exploits just because you haven’t rebooted your server.