Dropbox Stop Syncing on Linux

Dropbox may stop syncing on Linux without any error message. The issue may arise from 2 causes:

• The user does not have the privilege to access the files to be synced.
• Dropbox depends on file watching to get which file is edited and should be synced, but the system allows too few file watches.

In the second case, you may see the following warning when executing dropbox start:

Unable to monitor entire Dropbox folder hierarchy. Please run "echo fs.inotify.max_user_watches=100000 | sudo tee -a /etc/sysctl.conf; sudo sysctl -p" and restart Dropbox to fix the problem.

Which can be fixed by:

echo fs.inotify.max_user_watches=100000 | sudo tee -a /etc/sysctl.conf; sudo sysctl -p
dropbox stop
dropbox start

Supplementary

The file watching is also used in Visual Studio Code to track modifications in Git. It uses a larger number of file watches as shown in this link.