Have you ever considered automating basic tasks on your desktop, such as sending timely emails to friends or downloading files from a certain source?
Well, it's possible if you know job scheduling in operating systems.
In this article, I will show how to schedule a job in Linux (I will be using Ubuntu 22.04 here).
Cron
In Linux, "cron" command utility is used for job scheduling. Cron is derived from a Greek word "Chronos" meaning time. All the cron along with the task to be done, is stored in a crontab file.
The syntax of cron is given below
┌───────────── minute (0 - 59)
│ ┌───────────── hour (0 - 23)
│ │ ┌───────────── day of the month (1 - 31)
│ │ │ ┌───────────── month (1 - 12)
│ │ │ │ ┌───────────── day of the week (0 - )
│ │ │ │ │
│ │ │ │ │
│ │ │ │ │
* * * * * <command>
For example, if you want to represent "25 May 18:30", then it's cron representation will be
30 18 25 5 *
Using Crontab in Ubuntu
Let's run a Python script automatically using Crontab. I will write a Python program to make a simple GUI app using tkinter module.
from tkinter import *
window = Tk(className="App")
window.geometry("300x300")
label = Label(window, text="Hello World")
label.pack()
window.mainloop()
Now save this Python script in a directory and copy the file location.
Open terminal and type
crontab -e
This command will open Crontab file in that terminal (vim/nano/emacs editor based on your preference. I am using nano.).
Remove all the comments if you want.
Add an extra line in that file
43 13 25 5 * /usr/bin/python3 -u /path/of/file/script.py
Note: Specify the path of python3 interpreter (usr/bin/python3 in Ubuntu) while entering a job.
Execute whereis python3 in your terminal to get the path.
So, you will get a new window automatically on time.
There are many useful crontab commands, I will list out here.
crontab -e // opens a new crontab file
crontab -l // shows list of job scheduled
crontab -r // deletes user's crontab
crontab -h // to display list of commands available in crontab
Accessing Crontab using python-crontab module
Opening Crontab files and entering the jobs manually is a tedious task.
There is a module in Python python-crontab which helps to
schedule the job easily.
Install python-crontab.
pip3 install python-crontab
Create a new Python file. Import and initialise Crontab object with current user
from crontab import CronTab
cron = CronTab(user="<username>")
Note: Type whoami in terminal to get the username.
Set a new command using cron.new() function. Let's execute the same file.
job = cron.new("/usr/bin/python3 -u /path/of/file/script.py")
Now schedule the job.
job.minute.on(43)
job.hour.on(13)
job.day.on(25)
job.month.on(5) # That's 25th May 13:43
Save the changes.
cron.write()
Run this program and check crontab -l to ensure whether job is scheduled or not.
That's it! You have scheduled a job using Python.
Wait, hold on
This is my first article in dev.to. I was working on a project, then I came across job scheduling in Linux, which makes really easy to automate tasks. If you like this article, make sure you follow me on dev.to for more interesting articles.
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