How to Install Syncthing Remote File Synchronization Software on Debian 11

Syncthing is a free and open-source file syncing application used to sync files between multiple remote devices over the internet. It works on peer-to-peer architecture and exchanges the data automatically between two devices. It helps you to keep files and directories synchronized in real-time. All data transmission between multiple devices is safe and encrypted with TLS. It has clients for Linux, Windows, and macOS. It also has an Android app to sync from and to smartphones!

In this post, we will show you how to install Syncthing file synchronization software on Debian 11 server.

Prerequisites

  • Two servers running Debian 11.
  • A root password is configured on each server.

Add Syncthing Repository

By default, Syncthing is not included in the Debian 11 default repo. So you will need to add the Syncthing repository on both servers.

First, install the required dependencies using the following command:

apt-get install gnupg2 curl apt-transport-https -y

Next, download and add the GPG key with the following command:

curl -s https://syncthing.net/release-key.txt | apt-key add -

Next, add the Syncthing repository to APT with the following command:

echo "deb https://apt.syncthing.net/ syncthing release" > /etc/apt/sources.list.d/syncthing.list

Next, update the repository with the following command:

apt-get update -y

Install Syncthing on Debian 11

At this point, the Syncthing repo is added on both servers. Now, run the following command on both servers to install Syncthing.

apt-get install syncthing -y

Once the Syncthing is installed, verify the Syncthing version using the following command:

syncthing --version

You will get the following output:

syncthing v1.18.6 "Fermium Flea" (go1.17.6 linux-amd64) [email protected] 2021-12-30 12:07:01 UTC [noupgrade]

Create a Systemd Service File for Syncthing

Next, you will need to create a systemd service file on both servers to manage the Syncthing. You can create it with the following command:

nano /etc/systemd/system/[email protected]

Add the following lines:

[Unit]
Description=Syncthing - Open Source Continuous File Synchronization for %I
Documentation=man:syncthing(1)
After=network.target

[Service]
User=%i
ExecStart=/usr/bin/syncthing -no-browser -gui-address="0.0.0.0:8384" -no-restart -logflags=0
Restart=on-failure
SuccessExitStatus=3 4
RestartForceExitStatus=3 4

[Install]
WantedBy=multi-user.target

Save and close the file when you are finished. Then, reload the systemd daemon to apply the changes.

systemctl daemon-reload

Next, start the Syncthing service with the following command:

systemctl start [email protected]

Next, verify the status of the Syncthing using the following command:

systemctl status [email protected]

You will get the following output:

? [email protected] - Syncthing - Open Source Continuous File Synchronization for root
     Loaded: loaded (/etc/systemd/system/[email protected]; disabled; vendor preset: enabled)
     Active: active (running) since Mon 2022-01-31 02:28:35 UTC; 11s ago
       Docs: man:syncthing(1)
   Main PID: 2746 (syncthing)
      Tasks: 14 (limit: 2341)
     Memory: 56.3M
        CPU: 1.661s
     CGroup: /system.slice/system-syncthing.slice/[email protected]
             ??2746 /usr/bin/syncthing -no-browser -gui-address=0.0.0.0:8384 -no-restart -logflags=0
             ??2752 /usr/bin/syncthing -no-browser -gui-address=0.0.0.0:8384 -no-restart -logflags=0

Jan 31 02:28:36 server1 syncthing[2746]: [6F5DY] INFO: QUIC listener ([::]:22000) starting
Jan 31 02:28:36 server1 syncthing[2746]: [6F5DY] INFO: Loading HTTPS certificate: open /root/.config/syncthing/https-cert.pem: no such file o>
Jan 31 02:28:36 server1 syncthing[2746]: [6F5DY] INFO: Creating new HTTPS certificate
Jan 31 02:28:36 server1 syncthing[2746]: [6F5DY] INFO: Completed initial scan of sendreceive folder "Default Folder" (default)
Jan 31 02:28:36 server1 syncthing[2746]: [6F5DY] INFO: GUI and API listening on [::]:8384
Jan 31 02:28:36 server1 syncthing[2746]: [6F5DY] INFO: Access the GUI via the following URL: http://127.0.0.1:8384/
Jan 31 02:28:36 server1 syncthing[2746]: [6F5DY] INFO: My name is "server1"
Jan 31 02:28:36 server1 syncthing[2746]: [6F5DY] WARNING: Syncthing should not run as a privileged or system user. Please consider using a no>
Jan 31 02:28:36 server1 syncthing[2746]: [6F5DY] INFO: quic://0.0.0.0:22000 detected NAT type: Not behind a NAT
Jan 31 02:28:36 server1 syncthing[2746]: [6F5DY] INFO: quic://0.0.0.0:22000 resolved external address quic://69.87.219.167:22000 (via stun.sy>

By default, Syncthing listens on port 8384. You can check it with the following command:

ss -antpl | grep 8384

You will get the following output:

LISTEN 0      4096               *:8384             *:*    users:(("syncthing",pid=2752,fd=28))

Set Syncthing Admin Password

At this point, Syncthing is installed and running on both servers. Now, you will need to access the Syncthing web UI and set an admin password.

To set the admin password of the first server, open your web browser and access it using the URL http://first-server-ip:8384. You should see the following screen:

Set admin password in Syncthing

Click on the Settings button. You should see the following screen:

Settings

In the GUI tab, define your admin username, password and click on the Save button to apply the changes. You will be redirected to the Syncthing login page:

admin login

Provide your admin username, password, and click on the Sign in button. You should see the Syncthing dashboard on the following screen:

Syncthing GUI

To set the admin password of the second server, open your web browser and access it using the URL http://second-server-ip:8384. You should see the following screen:

Set GUI auth user

Click on the Settings button. You should see the following screen:

GUI settings

In the GUI tab, define your admin username, password and click on the Save button to apply the changes. You will be redirected to the Syncthing login page:

sign-in

Provide your admin username, password, and click on the Sign in button. You should see the Syncthing dashboard in the following screen:

Syncthing dashboard

Add Each Server to Another Server

Next, you will need to locate the device ID of each server and add it to another server in order to sync files between both servers.

On the first server dashboard, click on the Actions > Show ID to locate the device ID. You should see the following screen:

Connect servers to each other

On the second server dashboard, click on the Actions > Show ID to locate the device ID. You should see the following screen:

Server 2

On the first server, click on the close button. You should see the following screen:

Syncthing connected

Now, click on the Add Remote Device. You should see the following screen:

Server 2

Provide the device ID and name of the second server and click on the Save button. Once the device has been added, you should see the following screen:

Server 2 devices

On the second server, click on Add Remote Device. You should see the following screen:

Add device on server 1

Provide the device ID and name of the first server and click on the Save button. You should see the following screen:

Folders and servers

Create and Shared a Folder

Next, you will need to add and share the folder on the first server that you want to sync with the second server.

On the first server, click on the Add Folder button. You should see the following screen:

Add shared folder

Provide your folder label, folder path, and click on the Sharing tab. You should see the following screen:

Unshared devices

Tick to the second server and click on the Save button. You should see the following screen:

Shared folder has been synced

Next, go to the second server and click on Rescan All button. You should see the following screen:

Add new folder

Click on Add to add the folder shared on the first server. You should see the following screen:

Folder label

Click on the Save button to apply the changes. You should see the following screen:

Scanning folder

At this point, both servers are configured to sync file each other. Whenever you create or modify any files on the shared folder on the first server they will be synchronized automatically to the second server.

Conclusion

Congratulations! you have successfully installed and configured Syncthing on two Debian 11 servers and set up synchronization between both servers. I hope this tutorial will help you to backup your server. Feel free to ask me if you have any questions.

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By: Nick
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Thank you for the article on Syncthing!  I'm happy to see that more people are becoming interested in freedom and privacy respecting alternatives to the big commercial providers.  It's also great to see more documentation about how to set it up, because that's frequently said to be tricky.  This said, please note the following inacuracies:Two servers are not required.  Syncthing also works with laptops, desktops, workstations, and Android devices.Syncthing should be run with `systemctl enable --user syncthing` with an unprivileged user, and *never* as root. eg: principle of least privilege.  To run any network facing service as root is a huge vulnerability.  It may also be worth mentioning that multiple users may each run their own syncthing --user service, because newly created files are owned by the service process owner (eg: permissions are clobbered), and paths with more restricted permissions than 777 will be unreable and/or unwriteable by their intended owner.  When the first user has started the service, and a second user starts their own service, the second Syncthing instance configures itself to use a non-conflicting port.Syncthing has been part of Debian "main" (the default repo) since May 2016, and a user does not need to enable an external repo.  In other words, Syncthing was part of Debian 9 ("stretch").  Backports of the latest available version are made available to users of stable when the benefit is significant enough (eg: performance enhancements, bug fixes that don't meet the criteria for stable-updates, etc.).  Also, the Debian package includes a systemd service by default.