Crontab is used like
which launches a text editor (usually vi
) that you use to edit the crontab file (it's not
edited directly). Saving an empty file won't make any difference. Writing some garbage shouldn't kill anybody, those lines just aren't run (or if the time settings are ok but the command is garbage, it probably just produces an error). Each user has it's own crontab file, which is (afaik) run as that user, so if you need to do something system-wide, run crontab -e
I don't think you can mess anything really up with cron, except if you issued a bad remove command, so test the commands first out
Any user can use crontab, but they can't run anything they can't regularly run. Cron simply runs the given command(s) at the given time, as the user who created the crontab (root can create other user's crontab files too).
And if you happened to mess the crontab file up, just remove it (with crontab command!) and you're ok.