Odoo has an option to restart when python files are updated.

This is only useful during active development, and not an option that would be used on a production system.

For a full list of options that can be used via command-line or configuration files, see https://www.odoo.com/documentation/11.0/reference/cmdline.html

The warning is notifying you that this option is disabled due to a dependent Python module not being installed on the server.

To resolve, install the dependency (and restart the server).  

To install inotify on Ubuntu:

sudo pip3 install inotify​

If you run into any problems, you may need to increase the amount of inotify watchers as outlined in https://github.com/guard/listen/wiki/Increasing-the-amount-of-inotify-watchers

You may need to add the following line to /etc/sysctl.conf and restart your server.

fs.inotify.max_user_watches=52428