https://www.ostechnix.com/find-size-directory-linux/

https://www.marcus-povey.co.uk/2015/04/09/cross-server-ssh-rsync-backups-done-more-securely/

https://help.ubuntu.com/community/Fstab

https://stackoverflow.com/questions/8475694/how-to-specify-in-crontab-by-what-user-to-run-script

https://www.tecmint.com/rsync-local-remote-file-synchronization-commands/