Getting Started with Cron Scheduling
Cron Job Basics
Cron is a system process which is used to execute background tasks on a routine basis. Cron requires a file called crontab which contains the list of tasks to be executed at a particular time. All these jobs are executed in the background at the specified time
To view cron jobs running on your system, navigate to your terminal and type in:
crontab -l
The above command displays the list of jobs in the crontab file. To add a new cron job to the crontab, type in:
crontab -e
The above command will display the crontab file where you can schedule a job. Let’s say you have a file called hello.py which looks like:
print "Hello World"
Now, to schedule a cron job to execute the above script to output to another file, you need to add the following line of code:
50 19 * * * python hello.py >> a.txt
The above line of code schedules the execution of the file with output to a file called a.txt. The numbers before the command to execute define the time of execution of the job. The timing syntax has five parts:
- minute
- hour
- day of month
- month
- day of week
Asterisks(*) in the timing syntax indicate it will run every time.
* * * * * command to be executed
- - - - -
| | | | |
| | | | ----- Day of week (0 - 7) (Sunday=0 or 7)
| | | ------- Month (1 - 12)
| | --------- Day of month (1 - 31)
| ----------- Hour (0 - 23)
------------- Minute (0 - 59)