When running rsync you get an error a bit like this:
The authenticity of host '192.168.1.10 (192.168.1.10)' can't be established. ECDSA key fingerprint is 65:76:dc:ba:74:d6:c7:75:7f:21:58:c6:66:42:23:7d.
You need to add your key to the remote device to be trusted, then you won't get asked for password on each connection (a real pain when using scripts).
From the command line:
ssh-keygen Press enter for every prompt This will place your local key in the remote server
Then run this:
ssh-copy-id -i ~/.ssh/id_rsa.pub 192.168.1.10 Enter the remote server password
Now you should be able to ssh to the server without a password