Set Up and Use Syncthing to Sync Files on Linux

Syncthing is a powerful, decentralized, open-source file synchronization software that allows users to easily and securely synchronize files between different devices and platforms, including Windows, Linux, macOS, and Android, making it a versatile solution for individuals and organizations. In addition, it uses a peer-to-peer architecture, meaning that files are synchronized directly between devices without relying on a central server, making it a more secure and private option for file syncing.

The Syncthing UI gives users a graphical interface to configure and manage Syncthing instances running on their devices. With it, users can view the status of their synced folders, add or remove devices from the synchronization network, set up advanced synchronization options, and monitor the transfer of files between devices.

The UI is designed to be user-friendly and intuitive, with a clean and easy-to-use interface that makes it easy for users to manage their synchronized files and folders. Furthermore, it is accessible via a web browser so that users can access it from any device with an internet connection. This guide shows you how to set up your Syncthing instances to sync files between them. So let’s get started!

Step 1: Install Syncthing on Linux

Syncthing is available in most Linux distributions’ repositories, making installation simple. Depending on the distro you’re using, here’s how to install it.

Ubuntu, Debian, and all other Linux distros based on them and using their software repositories need to run:

sudo apt install syncthing

Fedora

If you are using Fedora, run the following:

sudo dnf install syncthing

Rocky Linux, AlmaLinux

Rocky Lynux, Alma Linux, and other RHEL-based users must first add the EPEL repository to their systems (if not already done) before installing Syncthing, which is housed in it.

sudo dnf install epel-release
sudo dnf install syncthing

Arch Linux, Manjaro, EndeavourOS

Users of Arch and its derivatives can install Syncthing with the following Pacman command:

sudo pacman -S syncthing

This guide will synchronize files between two computers running Ubuntu and Fedora. So let’s start by installing Syncthing on both machines.

On the Ubuntu machine, we run the following:

sudo apt install syncthing

Accordingly, on the Fedora machine, we perform the following:

sudo dnf install syncthing
Installing Syncthing on Fedora.

Once Syncthing is installed on our Linux systems, we’ll ensure the service starts automatically.

Step 2: Setting the Service to Start Automatically

We will set Syncthing to start automatically on every system boot. This gives us peace of mind that our files will always be in sync between systems without further intervention.

To do this, run the two commands listed below on each machine, remembering to replace the “myuser” part with your username on that system.

sudo systemctl enable syncthing@myuser.service
sudo systemctl start syncthing@myuser.service

Setting the Syncthing service to start automatically on our Ubuntu system.
Setting the Syncthing service to start automatically on our Fedora system.
Then, you can run the command below to check the service status on each machine, and the output should look like this.

sudo systemctl status syncthing@myuser.service

Check service status.
Of course, don’t forget to replace the “myuser” part again with the current username valid for your system.

Step 3: Syncthing Initial Configuration

Once we have ensured Syncthing is up and running on both Linux systems, we can configure it.

Syncthing provides an easy-to-use, user-friendly web interface to configure the service and synchronize files. It is accessible through a web browser on port 8384. So, on one of our two Linux systems, say Ubuntu, we point the browser to “http://localhost:8384“.

You will be greeted by the screen below, prompting you to choose whether you allow anonymous statistics to be sent. Make your choice to continue.

Allow anonymous usage reporting to be sent.
Here we will make a slight digression. If you have installed Syncthing on a headless Linux server, in other words, one that does not have a desktop environment, you may be wondering how you can configure the service. Don’t worry because the solution is straightforward. This is where SSH tunnels come to the rescue.

Open the terminal app you are using, and run the command below, where “XXXX” is the local port to which the remote “8384” port will be mapped. Also, replace “myuser” with the username valid for this system and the “remote-ip-address” part with the IP address of the Syncthing server.

ssh -L XXXX:localhost:8384 myuser@remote-ip-address

For example, the command would look like this:

ssh -L 8855:localhost:8384 linuxiac@192.168.122.26

In the example above, we map the local “8855” port on our desktop system to the remote “8384” port on the server with IP address “192.168.122.26” (in that case, our Ubuntu Syncthing instance) where we have installed and run Syncthing.

After successfully logging in, it is essential to remember that the terminal window from which you executed the SSH tunneling command must remain open for the tunnel to stay active.

You can then navigate to “http://localhost:8855” in the web browser on your desktop PC from which you ran the command. As a result, you will be taken to the remote machine’s Syncing admin interface.

But now, back to our Ubuntu system. First, you’ll see a reminder message that no password has been set to access the Syncthing UI. So, following best practices, let’s set one.

Click on the “Settings” button. Next, choose the “GUI” tab in the pop-up window, then enter your preferred username and password in the “GUI Authentication User” and “GUI Authentication Password” fields, and finally, confirm with “Save.”

Repeat the same steps on the second Syncthing instance, our Fedora system.

Step 4: Connecting the Syncting Instances

Let’s now connect our two instances, Ubuntu and Fedora, to each other. Syncthing uses a specially generated ID for each instance to identify itself as a unique identifier. Therefore, we must know and provide this identifier to connect one instance to another.

To connect the Ubuntu and Fedora Syncthing instances, first get the unique ID of one of the two, say Ubuntu, then enter it into the Fedora Syncthing instance.

Press the “Actions” button at the top right, and from the menu, choose “Show ID.”

Get Syncthing’s instance ID.

Copy the code shown from the pop-up window and switch to the other Syncthing instance, Fedora.

Get Syncthing’s instance ID.

On the second instance, select the “Add Remote Device” button.

Add a remote device.

Paste the copied code from the Ubuntu Syncthing instance into the “Device ID” field and click “Save.”

Add a remote device.

Now if you go back to the Ubuntu Syncthing instance, you’ll see that a message has appeared saying that the Fedora device wants to connect to it. Confirm by clicking on the “Add Device” button.

A new pop-up window will open where you can change the device name for your convenience. When you’re done, click the “Save” button to add it.

After a few seconds, the device status under the “Remote Devices” section should change to “Connected.”

If you go to the Fedora system, you’ll see that the status there has also automatically changed to the same.

Congratulations! Your two remote Syncthing instances are now connected. Let’s move on to the final part, syncing files between them.

Step 5: Setting up Syncthing Shares

By default, Syncthing creates an empty folder named “Sync” in your home directory to store files that will be shared with other Syncthing instances. Of course, you can add as many additional folders as you want using the “Add Folder” button, but we will stick with the default “Sync” folder for this guide. The sharing and syncing mechanisms are the same for each additional folder added.

Sync folder.

To set up a directory where you will share the files available in it with other Syncthing instances, click on “Edit.”

Set up Syncthing file sharing.

Select the “Sharing” tab from the open pop-up, then tick the box of the Syncthing instance with which you will be sharing/syncing files. In our case, this is the Fedora system we added a moment ago.

The following step is optional, but I strongly recommend it. It is all about file versions. Syncthing allows you to keep several versions of the same file. In some cases, this can be lifesaving, enabling you to restore a file that was accidentally overlapped with another or even deleted.

To take advantage of this unique feature, select the “File Versioning” tab, then choose “Simple File Versioning” from the drop-down menu, and for “Keep Versions,” I recommend setting “3.” When you’re done with the settings, confirm with the “Save” button, and the window will close.

This action will automatically notify the other Synthing instance that we want to share a folder with it. So when you go to the Fedora machine, you’ll see a notice asking you to confirm the folder share. Just hit the “Share” button, and the folder will be shared and kept in sync between the two Syncthing instances.

Step 6: Testing File Sync

We’ve come to the most exciting moment, where we’ll see the fruits of our labor. Both Syncthing instances have an empty “Sync” folder. So let’s put some files in the Ubuntu machine’s “Sync” folder.

Now go to the other Syncthing instance; in our case, it is the Fedora machine, and the magic has happened! The files you added to the Ubuntu system are now available in the “Sync” folder on the Fedora system.

The files are successfully synchronized with the other Syncthing instance.
Of course, synchronization works both ways, so no matter which instance you add, change, or delete a file from, it will be automatically replicated on the other within seconds.

Ref & Credit:
https://linuxiac.com/how-to-set-up-and-use-syncthing-to-sync-files/