I'm using different computers with Ubuntu on it. Sometimes I work on a desktop at home, sometimes on a Laptop, sometimes I use another desktop computer. When I switch machines it often happens that a file is on one computer, but not at the other one. So I manually synchronize them. What I'd like to do is to have some kind of automatic synchronisation between all machines. So when I add a file to one computer it should go to the other machines and when a file gets change also the change should move to all the other machines.
I don't want to use some kind of cloud storage (Dropbox etc.) and also a network file system is not the right way to go (no networking access at all times). What do you suggest to realise this?
You can use owncloud https://owncloud.org/ or nextcloud https://nextcloud.com/ instead of 3rd party cloud services (like dropbox).
You setup one of your PCs as a server and setup all the other PCs as clients (including the PC acting as server).
The "server" PC preferably should be a desktop, with a Gbit ethernet connection (not wifi) which should be always on or should be able to wake on lan.
As an alternative to having a PC always on, there are solutions based on Rasberry Pi's or other low energy boards. eg https://nextcloud.com/box/