wget http://download.proxmox.com/debian/proxmox-ve-release-6.x.gpg -O /etc/apt/trusted.gpg.d/proxmox-ve-release-6.x.gpg
 
echo deb http://download.proxmox.com/debian/pbs-client buster main > /etc/apt/sources.list.d/proxmox-pbs.list
apt update
apt install proxmox-backup-server

wget http://download.proxmox.com/debian/proxmox-release-bullseye.gpg -O /etc/apt/trusted.gpg.d/proxmox-release-bullseye.gpg
 
echo deb http://download.proxmox.com/debian/pbs-client bullseye main > /etc/apt/sources.list.d/proxmox-pbs.list
apt update
apt install proxmox-backup-server

#exporte le mot de passe de l'utilisateur ou le 
export PBS_PASSWORD=6a4faca3-cbb6-4310-b024-64c2b4214538
proxmox-backup-client backup test.pxar:/etc --repository test@pbs@pbs-srv:dstor
proxmox-backup-client backup test.pxar:/var/log  --repository test@pbs@pbs-srv:dstor --backup-id 102 --backup-type ct

• https://forum.proxmox.com/threads/how-to-install-proxmox-backup-client-under-ubuntu.81371/