cd ~pg_dump whatsspy -U postgres > whatsspy_backup.sql
(where whatsspy is the database name)
This command creates a file called whatsspy_backup.sql of the whole database in your home directory. You can copy this file over with for example WinScp (if you use SSH) or just copy it over to a USB drive.
Execute sudo crontab -e and comment out all lines (by setting # in front).
Execute sudo nano /home/whatsspy-public-startup and comment out the following lines (by setting # in front):
echo "[update] Checking for updates."
# Force pull
git fetch --all
git reset --hard origin/master