Last Updated on 2021-04-12 by Clay
Sometimes, we need to execute our program regularly, it’s like crawling financial news, waking us up, and sending us emails … etc.
In Linux, we can use crontab tool to help us set up a schedule to automatically execute programs. Today, I will simply record how to set up crontab to accomplish these functions.
crontab settings
We can use the following command to check our schedule.
crontab -lIf you output is:
no crontab for "user_name"That mean you have no any process wait to executed.
How should we set up crontab? We can start writing with the following command:
crontab -eIf the editor for editing crontab is not familiar to you, you can use export EDITOR="EDITOR_NAME" to set the editor you want to use. For example, if you are used to using vim, then you can use export EDITOR=vim .
After starting to edit, we will see the content like this:
We need to set the five field of
- minute (0-59)
- hour (0-23)
- day of month (1-31)
- month (1-12)
- day of week (0-6)
- COMMAND
And * symbol means EVERY.
For example, I have a test.sh file that I want to execute, and I want to execute it once every day at 12 o’clock in the morning, then I have to write the following command:
* 0 * * * sh /home/clay/test.shIf I have a test.py Python program that I want to execute it every 5 minutes, then I can write:
*/5 * * * python3 /home/clay/test.pyIn order to prevent errors, it is best to use the absolute path setting for the program to be executed.
References
- https://docs.oracle.com/cd/E19455-01/805-7229/6j6q8svfo/index.html
- https://man7.org/linux/man-pages/man5/crontab.5.html