Dropbox gives me pop-up errors about not being able to monitor the file system (that quickly disappear) when it starts up but it still seems to work ok, why is that?
On Linux, the Dropbox client is subject to a default system limit on the number of directories it can monitor for changes. There is a warning regarding this, along the lines of:
Unable to monitor filesystem
Please run: echo 100000 | sudo tee /proc/sys/fs/inotify/max_user_watches and restart Dropbox to correct the problem.
This comes up often in the Dropbox Forums, and they have a mention of it in their "Why aren't certain files on one computer syncing to another?" document:
Monitoring more than 10000 folders
The Linux version of the Dropbox desktop application is limited from monitoring more than 10000 folders by default. Anything over that is not watched and, therefore, ignored when syncing. There's an easy fix for this. Open a terminal and enter the following:
> echo fs.inotify.max_user_watches=100000 | sudo tee -a /etc/sysctl.conf; sudo sysctl -p
This command will tell your system to watch up to 100000 folders. Once the command is entered and you enter your password, Dropbox will immediately resume syncing.