Cron is a time-based job scheduler in Linux and Unix.
Basic usage
Read the manual:
$ man crontabLoad your personal crontab (cron table) file:
$ crontab -eView your personal crontab:
$ crontab -lSyntax:
| min | hour | day of month | month | day of week | command |
| * | * | * | * | * | command |
| 0 – 59 | 0 – 23 | 1 – 31 | 1 – 12 | 0 – 6 (0 to 6 are Sunday to Saturday) | shell command you want to run at that time |
Intervals:
*/Nis the syntax for an interval- You can use commas if the interval is irregular
Time Syntax Examples
| Example | Explanation |
0 9 * * 1-5 |
Run Monday through Friday at 9am server time |
0 15 * * * |
Run every day at 3pm server time |
30 */2 * * * |
Run every 2 hours, on the half hour |
0 0 1 1 * |
Run once a year at midnight on January 1 |
0 3,7,12,18 * * * |
Run daily at 3am, 7am, noon, and 6pm |
Full example
Download a JSON file from Quandl and overwrite GOLD.json with it Monday through Friday at 5pm server time:
0 17 * * 1-5 wget -O "/path/to/quandl_data/GOLD.json" "https://www.quandl.com/api/v3/datasets/LBMA/GOLD.json"Things to look out for
- Surround anything with possible odd characters or spaces with quotes: URLs, local file paths, etc. This will keep you from getting errors.
- Use a full file path from root instead of
~/– Tildes aren’t interpreted the same way as on the command line - Times are always in server time. If you don’t know what time it is on the server, run:
$ date
Thanks goes out to Eric Davis for helping me out with this!
Leave a Reply