from="the.one.backup.server",command="${HOME}/.ssh/ssh_validate.sh",no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty ssh-rsa AA...Rw== some-note-about-this-key

##</code><code>##

#!/bin/sh
case "$SSH_ORIGINAL_COMMAND" in
        *\&*) echo "Rejected" ;;
        *\;*) echo "Rejected" ;;
        rsync*) $SSH_ORIGINAL_COMMAND ;;
        *) echo "Rejected" ;;
esac