linux - how to synchronize two directories to have the same contents?
Unidirectional
rsync is the right tool for mirroring (one directory is the source and the other one is the target).
But a question persists: How to know when a file was changed?.
Bidirectional
Another interesting tool that synchronizes directories in a bidirectional way is unison.
Warning
When installing unison with apt install it doesn't come with the file system monitoring tool.
The solution is to download the binaries from the github releases page.