Dropbox stops syncing

Solution if you have a lot of files in your Dropbox.

Dropbox no longer works well under Linux if you have a lot of files.
Solution:

Add this line
fs.inotify.max_user_watches = 5000000
to this file:
/etc/sysctl.d/99-sysctl.conf

Then do this to reload the kernel parameters:
sudo sysctl --system