As of Proxmox VE 5.0, there are two backup options included out of the box:

• Full backup: This backs up the entire virtual machine
• Snapshots: This freezes the state of a VM at a point in time

Proxmox 5.0 can only do a full backup and cannot do any granular file backup from inside a virtual machine. Proxmox also does not use any backup agents for guest VMs.