I have just managed to figure out an oddity with crontab on a newish Red Hat
Enterprise Linux machine. When ever I typed in
crontab -e to edit the crontab
it would open up an empty file rather the existing crontab. It turns out I needed
to add in an EDITOR environment variable in my bash profile.
Once the EDITOR environment variable was there everything worked. The annoying thing was that you don’t know there is a problem till the second time you edit your crontab at which point you instinctively close down the editor and crontab writes the empty file to your crontab, deleting the one you already had.