A typical cronjob for backing up just a root filesystem, once a day starting at 1AM, would look like the following. If a single backup takes longer than
24 hours, another will not be started concurrently, because of the just-one. You can edit this line into root's crontab by su'ing or sudo'ing
to root, and running crontab -e. The crontab -e command will put you into a text editor, in which you'll create a new line with the text below:
0 1 * * * find / -xdev -print0 | /usr/local/bin/just-one --command "/usr/local/bin/backshift --save-directory /backshift-production/save-directory --subset just-slash --backup --progress-report none" --string "backshift-just-slash"