When to run a cron job.
The Daily, Monthly, and Weekly options allow the cron job to be run by anacron, which is useful for non-servers.
Installs a cron job, that will run as a specified user in a particular directory. Note that the Desc must be unique, as it is used for the cron job filename.
Only one instance of the cron job is allowed to run at a time, no matter how long it runs. This is accomplished using flock locking of the cron job file.
The cron job's output will only be emailed if it exits nonzero.
Installs a cron job, and runs it niced and ioniced.