For preserving output from cron jobs: https://github.com/dc25/loggedcron

In all its glory:

loggedcron.bash view raw


So, for example, if you want a record of how much free space you have every night at 1:02, enter the following in your crontab (with appropriate changes of course):

02 01 * * * /home/dave/bin/loggedcron.bash df -k