I made a flask app following flask's tutorial. After
ctrl + c
Since you are using apache so in order to stop your app, you have to disable it by deleting .conf file from '/etc/apache2/sites-enabled/' folder and then restart the apache server. This will surely destroy your current running session.
$ cd /etc/apache2/sites-enabled/ $ sudo rm conf_filename.conf $ sudo service apache2 restart
Try it and your site will be down. To enable it again, copy paste your file to '/etc/apache2/sites-available/' and run the following commands to enable it again.
$ sudo a2ensite conf_filename.conf $ sudo service apache2 restart
Now your site will be live again.