Where is the crontab in Ubuntu?

  If you’re looking to make a copy of a user’s crontab as a backup or just to view it without using the crontab editor, you can locate it at:  
/var/spool/cron/crontabs
  Each user’s crontab will be in this directory in a file named as their username (e.g. root). If you’re working with a lengthy crontab it’s a good idea to back it up – can save you a lot of work if everything goes pear-shaped.