This documents gives details about the cronjob run options:
This field follows the syntax of cron (with minor differences). Specifically, each line consists of 5 fields separated by TAB or whitespace:
MINUTE HOUR DOM MONTH DOW
|MINUTE||Minutes within the hour (0–59)|
|HOUR||The hour of the day (0–23)|
|DOM||The day of the month (1–31)|
|MONTH||The month (1–12)|
|DOW||The day of the week (0–7) where 0 and 7 are Sunday.|
To specify multiple values for one field, the following operators are available. In the order of precedence,
*specifies all valid values
M-Nspecifies a range of values
*/Xsteps by intervals of X through the specified range or whole valid range
A,B,...,Zenumerates multiple values
To allow periodically scheduled tasks to produce even load on the system, the symbol
H (for “hash”) should be used wherever possible. For example, using
0 0 * * * for a dozen daily jobs will cause a large spike at midnight. In contrast, using
H H * * * would still execute each job once a day, but not all at the same time, better using limited resources.
H symbol can be used with a range. For example,
H H(0-7) * * * means some time between 12:00 AM (midnight) to 7:59 AM. You can also use step intervals with
H, with or without ranges.
H symbol can be thought of as a random value over a range, but it actually is a hash of the job name, not a random function, so that the value remains stable for any given project.
Beware that for the day of month field, short cycles such as
H/3 will not work consistently near the end of most months, due to variable month lengths. For example,
*/3 will run on the 1st, 4th, …31st days of a long month, then again the next day of the next month. Hashes are always chosen in the 1-28 range, so
H/3 will produce a gap between runs of between 3 and 6 days at the end of a month. (Longer cycles will also have inconsistent lengths but the effect may be relatively less noticeable.)
Empty lines and lines that start with
# will be ignored as comments.
@hourly are supported as convenient aliases. These use the hash system for automatic balancing. For example,
@hourly is the same as
H * * * * and could mean at any time during the hour.
@midnight actually means some time between 12:00 AM and 2:59 AM.
# every fifteen minutes (perhaps at :07, :22, :37, :52) H/15 * * * * # every ten minutes in the first half of every hour (three times, perhaps at :04, :14, :24) H(0-29)/10 * * * * # once every two hours at 45 minutes past the hour starting at 9:45 AM and finishing at 3:45 PM every weekday. 45 9-16/2 * * 1-5 # once in every two hours slot between 9 AM and 5 PM every weekday (perhaps at 10:38 AM, 12:38 PM, 2:38 PM, 4:38 PM) H H(9-16)/2 * * 1-5 # once a day on the 1st and 15th of every month except December H H 1,15 1-11 *