File synchronization between operating systems

SyncThing is an open-source software, secure, and capable of synchronizing files in near real-time across various operating systems (Windows/Linux/MacOS/Raspbian...) without intermediaries (no websites between your machines).

The software is configured through the browser (once installed, the software is accessible via port 8384).

Installations

• On each machine, you need to install the version of SyncThing dedicated to the operating system. For example, on a Raspberry Pi, you can open the package manager, search for SyncThing, and install it.
  
• Then launch the software: access it through the browser by going to the URL http://127.0.0.1:8384.
• On each system, in "Other Devices," add the system of the other machine.
  
• To proceed with sharing, choose a directory to share from one of the machines and create a share from that machine:
  
  
• In the "Shares" tab, check the system that will benefit from the share:
  
• In the Exclusions tab, you can add files or directories to exclude (below, exclusion of all files and subdirectories from "commun").
  
  
• In the "Advanced" tab on Synology, make sure the "Ignore permissions" checkbox is checked to avoid deleting rights.
  
• Once this screen is confirmed, go to the other machine on SyncThing. You should see a window indicating that you are invited to a new share. Click on Add.
• You are now prompted to create the destination for this new share, using the identifier created on the first machine in order to synchronize them.

Synchronizing machines that are not powered on at the same time

One scenario that may arise is wanting to synchronize machines when they are not powered on simultaneously. A NAS is particularly useful here as it serves as an intermediary.

Installation of SyncThing on a Synology NAS

If your NAS is a Synology type, the proprietary Synology Drive Client software allows you to synchronize files via a NAS on a Windows/Linux/macOS machine. However, in the context of a Raspberry Pi solution, this software may not be available or compatible. This is where SyncThing becomes particularly useful, as it is available on certain distributions for Raspberry (notably Raspbian).

• Open Synology DSM
• Go to the package manager and search for SyncThing (a version is available in the community packages). Then install it.
  
• Create an ID/password for the application, which will then be used to configure it from your PC.
• Next, go to the Control Panel, Shared Folder. Select the folder that will serve as an intermediary, click on Edit, and go to Permissions.
• Add read and write rights to the user "sc-syncthing" on the shared folder (this user was created by SyncThing and is visible in "Internal System Users"). Note that permissions must be allocated on the shared folder, not on a specific subdirectory of that shared folder.
  
• Then go to http://<NAS IP>:8384, and enter the ID/password created during the installation.
• Add the devices and create a share, as outlined in the installation section.
• If an error message indicates a permissions issue, it means that the step regarding the user sc-syncthing has not been followed correctly.
  
  
• If everything went well, you can modify the SyncThing service by going to a terminal (replacing "username" with the dedicated user account):
  systemctl enable syncthing@utilisateur.service
  systemctl start syncthing@utilisateur.service
  
  

You can effectively use Synology Drive Client between your PC and the NAS, and SyncThing between your NAS and a Raspberry Pi, with all file transfers occurring seamlessly and almost immediately in both directions.

Installation of SyncThing on Android

There is an official version of SyncThing on Android, but it was abandoned at the end of 2024 because the developer grew tired of the permissions restrictions imposed by Google, forcing him to rewrite parts of the application. A new version, Syncthing-Fork, has taken up the mantle.

After installation and configuration, you may encounter "permission denied," "Unsynchronized," or "Your version of Android grants SyncThing only read-only access to the selected directory." To work around this permission issue, create the following directory and use it as the synchronization point:

/storage/<id carte sd>/Android/media/com.github.catfriend1.syncthingfork/<nom du partage>

You will need to delete and recreate your share to do this.