If I type crontab -l in the command-line I can see the following line:
# * * * * * /usr/bin/php /home/user/every_minute_script.php
To start this cronjob, I need to edit the file using crontab -e command, remove the comment character at the beginning of the line, save the edited file, and exit the editor.
To stop this cronjob, the same steps, but adding the comment character at the beginning of the line.
I want to achieve exactly the same effect using a PHP script, instead of manually editing the file.