Error: Nach Umbennen eines Proxmox Node fehlten plötzlich alle VMs und im Log standen seltsame Fehler: ipcc_send_rec failed: Connection refused
Powerdown all VMs and containers
Edit /etc/hostname and /etc/hosts with the new hostname
Reboot the host
At this point you will see your old host as „disconnected“ in the web interface, and a new host with your new hostname appears.
SSH into the machine and navigate to /etc/pve/nodes – here you will see two folders (one with your new hostname, one with your old hostname)
The config for the containers is located at /etc/pve/nodes//lxc
The config for virtual machines is stored at /etc/pve/nodes//qemu-server
etc. depending on what other technologies you are using
So I just moved the contents of each folder into the folder for the new host – i.e. /etc/pve/nodes//lxc etc.
The second I did this, I saw the web interface update with the VMs and containers now showing in the correct datacenter and under the correct host.
Finally, move the folder with the old server’s hostname (/etc/pve/nodes/) somewhere for backup.
Source: Proxmox Forum