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Cron is driven by a crontab (cron table) file, a configuration file that specifies shell commands to run periodically on a given schedule. On linux systems you can run the crontab -e
command to edit.
# ┌───────────── minute (0 - 59) # │ ┌───────────── hour (0 - 23) # │ │ ┌───────────── day of month (1 - 31) # │ │ │ ┌───────────── month (1 - 12) # │ │ │ │ ┌───────────── day of week (0 - 6) (Sunday to Saturday; # │ │ │ │ │ 7 is also Sunday on some systems) # │ │ │ │ │ # │ │ │ │ │ # * * * * * command to execute
The syntax of each line expects a cron expression made of five fields, followed by a shell command to execute.
Expression | Description |
---|---|
*/5 * * * * |
Every 5 minutes show |
0 */8 * * * |
Every 8 hours show |
1,5 * * * * |
Minutes 1 and 5 of each hour show |
1-5 * * * * |
Minutes 1,2,3,4 and 5 of each hour show |
0 2 * * * |
Once a day at 2 am show |
0 1 * * 1,2 |
Monday and Tuesday at 1 am every week show |
0 0 * * 1 |
Every Monday at midnight show |
0 0 1 * * |
Day 1 of each month at midnight show |
0 0 */5 * * |
Every 5 days show |