Rename Proxmox node with existing VMs

Please note that I have only tried this on a single Proxmox node, and NOT a node joined to a cluster.

Change to the new hostname in the following 3 files:

nano /etc/hosts
nano /etc/hostname
nano /etc/postfix/

Reboot Proxmox.

Next, copy the VMs and configuration to the new hostname folder:

cd /etc/pve/nodes/
cp -r old_hostname/qemu-server new_hostname/qemu-server
rm -r old_hostname
cd /var/lib/rrdcached/db/pve2-node/
cp -r old_hostname new_hostname
rm -r old_hostname