crontab The most important thing about the crontab manpage is the order in which the timing controls occur. There are six columns at the start of every command in the crontab. These are the time controls. It is normal to see asterisks in most of the time controls; an asterisk means "every" or "this column doesn't matter". But that doesn't make a lot of sense until you grok the time controls: 1. Minute (0-59) 2. Hour (0-23) 3. Day of the month (1-31) 4. Month of the year (1-12) 5. Day of the week (0-6 with 0=Sunday) So a command starting with "5 * * * *" means "run this commmand at 5 minutes after the hour every hour, every day, every month, every week." A command starting with "30 5 * * *" means "run this command at 5:30 am every day every month every week". A command starting with "*/5 * * * *" means "run this command every 5 minutes every hour, every day, every month, every week." (But some versions of cron will not allow this syntax.)