Scheduling tasks using Cron: Difference between revisions

Revision as of 18:22, 26 December 2021

In this lesson we are going to learn how to automate routine tasks on the Raspberry Pi.
This is helpful is ever you need to back up files, upload content to a web server or sample data from a sensor.
Cron is a program that was designed to schedule routine tasks (commands, scripts or programs) on Linux systems, such as the Raspberry Pi.
The command crontab is used to edit the list of scheduled tasks.
Each user on the computer has their own cron table, so you can think of cron as your own personal assistant.
In this lesson we will automate the running of the atm_sensor_get.py python program using cron.

Running python programs from the Terminal
Learn how to find the directory path to applications and programs on your computer
Learn how to use the text editing software nano
Learn how to create scheduled tasks in cron

In this example we are going to run the atm_sensor_get.py program using the Terminal.
Up to now, we have only run python programs from within the Python3 IDLE3 environment.
To run our atm_sensor_get.py program we will use the command python3.

From the Raspberry Pi top bar menu click on the Terminal icon.
Once in your default home directory (/home/pi) enter ls to list all contents.
Find your project’s directory (e.g. botanica-park-lake) and use the change directory (cd) command to enter the directory (e.g. cd botanica-park-lake)
Enter the command ls to list all directory contents.

You should see the python file atm_sensor_get.py
To run this file, enter the command python3 atm_sensor_get.py
- python3 – name of application
- atm_sensor_get.py – script or program to run
The printouts we can see in the Terminal are the outputs from print() statements within our python code.

In this example we will find the path of the python3 application and scratch on the Raspberry Pi.
A path shows the location where a software application can be found within the directory structure on your computer.
To find the path for an application we use the Terminal command which followed by the name of the software application.

From the Raspberry Pi top bar menu click on the Terminal icon.
Once in your default home directory (/home/pi) enter ls to list all contents.
Find your project’s directory (e.g. botanica-park-lake) and use the change directory (cd) command to enter the directory (e.g. cd botanica-park-lake)
Enter the command ls to list all directory contents.

To find path to a current directory enter the command pwd (present working directory).
This is helpful when we need to know the path to a program we have written.
In this case, the path to the botanical-park-lake directory is /home/pi/botanica-park-lake
The full path to the atm_sensor_get.py program is /home/pi/botanica-park-lake/atm_sensor_get.py

We can find the path to other commonly used Linux commands.
For example, the command ls is also an application. To find its path enter which ls
The directory path to the ls application is found in the /bin directory (short for binary files)

@@ Line 59: / Line 59: @@
 [[File:Screen Shot 2021-12-27 at 5.16.33 am.png]]
+* Try this with other commands such as '''cat, cd, touch and pwd'''.
+* Do you see a pattern?
+* You can find other commands here: Linux commands - [[https://www.raspberrypi.com/documentation/computers/using_linux.html#linux-commands]]
+* You can also find the path to other programming applications, such as Scratch
+* Enter the command '''which scratch'''
+[[File:Screen Shot 2021-12-27 at 5.21.56 am.png]]