Back up and synchronise with rsync

Copy only what changed, locally or over SSH.

1. Dry run first (writes nothing):

   rsync -aHAXv --dry-run --delete /home/moi/Documents/ /media/disque/Documents/

   Copy
2. If the result is what you expect, run again without --dry-run:

   rsync -aHAXv --delete /home/moi/Documents/ /media/disque/Documents/

   Copy
3. To a remote server over SSH:

   rsync -aHAXvz -e ssh /home/moi/Documents/ utilisateur@serveur:/sauvegardes/documents/

   Copy
4. The trailing "/" on the source matters: with it, the folder's contents are copied; without it, the folder itself.
5. Automate with cron and keep several versions with the --backup-dir option.