Remarkable2

/home/root/ folder is the only folder that stays intact even after upgrades. And this folder will be backed up.

SSH Access

Go to Settings > Help > Copyright and licenses and the password is underneath GPLv3 Compliance header.

Copy the SSH public key into ~/.ssh/authorized_keys. The folder and file permissions need to be 700 for the folder and 600 for the file.

Create public key

This is needed to be only once in the beginning.

$ dropbearkey -t rsa -f ~/.ssh/id_rsa
$ dropbearkey -y -f ~/.ssh/id_rsa | grep "^ssh-rsa " >> ~/.ssh/id_rsa.pub

Backing up to a Synology server via rsync

Copy the public key to the target server, and then you'd need to enable rsync service under Control Panel > File Services > rsync. Once that's done, you can use the following command. This assumes that the target folder exists.

$ rsync -avz --progress -e "ssh -i $HOME/.ssh/id_rsa" /home/root/ myuser@mysynology.server:/var/services/homes/myuser/Backup/remarkable2/