I want to synchronize two folders between two Ubuntu computers but all my web searches come up with ideas to synchronize over the web, but I do not want to do this. The two computers are physically next to each other, so what I want to do is connect them together with a cable and then synchronize. How do I do this, and what sort of cable would I need?
If you connect the two with a cross-over RJ-45 cable (give them IP addresses in the same range, like 192.168.0.10/255.255.255.0 and 192.168.0.11/255.255.255.0), then use a tool like Unison (in the respositories), you should be able to synchronise what you like.
sudo apt-get install unison-gtk
This method needs that "special" cross-over cable, but removes the need for a hub or switch and certainly, there's no need for a router or internet access.
The network-manager lets you connect computers together directly. If you right-click on its icon and select 'edit connections', you can select 'auto eth0' under the tab and click on the 'edit' button. The 'IPv4 Settings' tab in the window has a box labelled 'method', from it you can select 'shared to other computers.' If you do this to one computer and connect the other to it (no crossover cable needed), it will act like a router and you should be able to transfer files by whatever method that way. It will also share its wireless internet connection (if it has one) to the other computer. I don't know if you have to change it back to connect normally.
This is what I use to connect my laptop to the old desktop I use to hold my backups, your mileage might vary though. I usually use avahi and an ftp server to connect, but this requires files to be transferred manually, Unison should suit your purposes better.