Questions[cron](ubuntu)

I have a fresh install of Ubuntu 12.04.1 LTS an a number of servers.

I have not added any cron jobs or edited my crontab on those servers, however, at around the same time for each machine, I get a 75% CPU spike and the following info in my syslog at the time of the spike:

CRON[8380]: (CRON) info (No MTA installed, discarding output)

I have mono-complete installed and am running a service stack webserver.

What is the best way for me to stop this from happening? I would like to be able to remove the CPU spike.

Since upgrading my user's crontab has been wiped out. This is not the first time this has happened this year and it's a pain restoring it each time.

I'd like to be able to back up the crontab for my user but for that I need to know where it's stored.

I want to verify that my cron job is executing and at what time. I believe there is a log for my sudo crontab -e jobs, but where?

I searched google and found recommendations to look in /var/log (in which I do not see anything with 'cron' in the name) and to edit the file /etc/syslog.conf which I also do not have.

Often, crontab scripts are not executed on schedule or as expected. There are numerous reasons for that:

1. wrong crontab notation
2. permissions problem
3. environment variables

This community wiki aims to aggregate the top reasons for crontab scripts not being executed as expected. Write each reason in a separate answer.

Please include one reason per answer - details about why it's not executed - and fix(es) for that one reason.

Please write only cron-specific issues, e.g. commands that execute as expected from the shell but execute erroneously by cron.

I want to schedule a task to run on a regular basis and have heard that Cron is the way to do this.

How do I add Cron jobs in Ubuntu?