Question: I would like to do a two-way automatic sync between folders `Directory A` and`Directory B`. This means that whenever a file in `Directory A` or one of its sub-directories is changed, that change is immediately applied to `Directory B`, and whenever a file in `Directory B` or one of its sub-directories is changed, that change is immediately applied to `Directory A`. Thus, the two directories would be completely identical, including document properties. How can I achieve this?

I am using Ubuntu 16.10. 

Symlinks are not an option.

Answer: 
For a long time I used rsync to sync my laptops(2) and a 3rd machine, then I tried with [syncthing](https://syncthing.net/) but this morning a famous search engine offered me this project:

[Mirror](https://github.com/stephenh/mirror)
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> Mirror is built to support a two-machine (e.g. desktop+laptop) development workflow where you want to run a command line compile/build process on a powerful/dedicated desktop, but still edit files remotely on a laptop.
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You will also find a comparison of different solutions.

His main argument against **rsync** are : not real time and nor *officially* two ways.

*PS: I'm using it through zerotier, so my machine are always able to communicate together.*
I come late on that question : to do that task often on the same folders, there is [Synchrorep](https://small-iceberg.dev/synchrorep).