Cron
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Cron is a job-scheduler in Unix-like Operating Systems.
Users set-up cron jobs to run at periodically at fixed times, dates and intervals.
Crone implementations
- cronie
- fcrone
- dcrone
- vixie-cron
- scrone-git
Usage
edit your cron-jobs by running:
crontab -e
each line of crontab file represents a job and is formatted like this:
* * * * * <command to execute> # | | | | | # | | | | day of the week (0–6) (Sunday to Saturday; # | | | month (1–12) 7 is also Sunday on some systems) # | | day of the month (1–31) # | hour (0–23) # minute (0–59)
Crontab uses the following symbols
| Symbol | Description |
|---|---|
| * | specifies every possible time interval |
| , | List multiple values separated by a comma. |
| - | specify a range between two numbers |
| / | Specify a periodicity/frequency using a slash |
Crontab also has some special keywords:
| Keyword | Description |
|---|---|
| @reboot | at startup |
| @yearly | once a year |
| @anually | identical to @yearly |
| @montly | once a month |
| @weekly | once a week |
| @daily | once a day |
| @midnight | identitcal to @daily |
| @hourly | once an hour |
Basic cron commands
| Command | Description |
|---|---|
| crontab -l | list your cronjobs |
| crontab -e | edit your cronjobs |
| crontab -r | remove all your cronjobs |