2 Working With cron

Use cron to schedule jobs that run at fixed times, and as often as every minute.

System cron jobs are defined in the cron table in the /etc/crontab configuration file, or in job files stored in the /etc/cron.d directory.

User defined cron jobs are stored in the /var/spool/cron directory and include the user's name in the file name, for example /var/spool/cron/jsmith for the user jsmith.

The crond daemon, which uses the cron utility to run scheduled jobs, checks those locations to decide which jobs need to run.

If the crond daemon identifies a job that was configured to run in the current minute, then the crond daemon runs that job as the owner of the job definition. If the job is a system cron job, then the daemon runs the job as the user that's specified in the job definition, if the user is defined.

If the system is down when a cron job is scheduled to run then, when the system is restarted, the daemon skips that job until the next scheduled run.