Commands are executed by cron when the minute, hour, and month fields match the current time, and at least one of the two day fields (day of month, or day of week) match the current time. A field may be an asterisk (*), which will always match.

Field	Allowed values
minute	0-59
hour	0-23
day of month	1-31
month	1-12 or first three letters
day of week	0-7 or first three letters (0 or 7 is Sunday)

Examples

Run every Tuesday at 2:30

30 2 * * tue /path/to/command

Run every 10 minutes

*/10 * * * * /path/to/command

Run every 2 hours, on the half hour

30 */2 * * * /path/to/command

Run every 2 hours, on the half hour, but only on weekdays

30 */2 * * 1-5 /path/to/command

Run at 12:05, 13:05, ..., and 18:05

5 12-18 * * * /path/to/command

Run at 12:05, 14:05, 16:05, and 18:05

5 12-18/2 * * * /path/to/command

Run on the first day of every month, at midnight

0 0 1 * * /path/to/command

Run on the first day of every third month, at midnight

0 0 1 */3 * /path/to/command