On the synology, I used the SynoCommunity borgbackup package. Once installed, go create a shared folder named “borgbackup”. Then, the trick is to create a specific RSA key that will be used by SSH to authenticate the backup user. You can create a specific group/user for your backups, I was lazy to do so and I don’t think it has much benefits. I’ll therefore use my computer username to connect. Once the key is created with ssh-keygen -f ~/.ssh/id_rsa_borgbackup -C "borg@pm.me", I copied the key to the synology in ~/.ssh/authorized_keys. Note that the synology home directory needs 755 permissions, as always ssh permissions should be: