I found two starting solutions:use Unison, but I found no way to install this package on a Nas Synology via DSM.use Cloud Station Drive, but Synology only propose packages for Fedora and Ubuntu and I don't found an URL package source to install the Ubuntu package with apt-getShould I dig one of these solutions or is there an other alternative solution? 
How to sync bidirectionaly 2 folders between a Synology Nas and a Debian computer?
debian;synchronization;nas;unison;synology