Using Syncthing on Android: Syncthing-Fork Setup and Photo Backup

Syncthing Series

On Android, there are two common ways to use Syncthing:

The original Syncthing Android client.
The community-maintained Syncthing-Fork.

Both can work for basic use. For long-term syncing of photos, notes, or documents, Syncthing-Fork is usually the better choice. It offers more practical controls for Android background behavior, battery usage, and network conditions, including Wi-Fi-only sync, selected Wi-Fi SSIDs, and running only while charging.

This article combines general Android setup with photo backup. Photo backup is one of the most common mobile Syncthing workflows, but it should not be configured like an ordinary two-way sync folder.

Why Syncthing-Fork Is Usually Better

Android actively restricts background apps. After the screen turns off, the system may suspend networking, freeze processes, or kill background services. If a sync tool does not handle this well, it may only sync while the app is open.

Syncthing-Fork is more practical for phone use because it can:

Set run conditions.
Sync only on Wi-Fi.
Sync only on selected Wi-Fi networks.
Run only while charging.
Fit Android’s background restrictions better.

This does not mean the original client is unusable. It simply means Syncthing-Fork is better tuned for long-running mobile sync.

Installation Sources

Common sources include:

Google Play
F-Droid
GitHub Releases

Choose the channel you trust. After installation, handle permissions and background settings before pairing devices.

Step 1: Grant Required Permissions

On first launch, focus on two permission areas.

Storage Permission

For file synchronization, Syncthing-Fork must be able to read and write target folders.

Recent Android versions may ask for all-files access or similar storage access. Without it, the app may only see a limited set of folders and fail to read photos, documents, or your chosen sync directory.

Recommendations:

Grant the required file access permissions.
Put sync folders under ordinary internal-storage directories.
Avoid protected system directories.

Useful examples:

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/storage/emulated/0/SyncData
/storage/emulated/0/SyncData/Notes
/storage/emulated/0/SyncData/Photos

For camera photos, the common path is:

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/storage/emulated/0/DCIM/Camera

Battery Optimization Allowlist

This is the most important Android-specific step.

If Syncthing-Fork is not excluded from battery optimization, Android may kill the sync process after the screen locks. The result is simple: you think it is syncing in the background, but it only moves when you open the app.

Add Syncthing-Fork to the system battery optimization allowlist. The setting name depends on the vendor:

Not optimized
Allow background running
Allow auto start
Lock in background
Allow high background power usage

Many Android vendor builds add extra background and auto-start restrictions. If sync is unstable, check both battery management and auto-start settings.

Step 2: Pair with a NAS or Computer

Syncthing pairs devices by adding each other’s device ID.

Assume the phone is device A and the NAS or computer is device B.

On the phone:

Open Syncthing-Fork.
Open the menu.
Show the device ID.
You will see a QR code and a long device ID.

On the NAS or computer:

Open the Syncthing Web GUI.
Click Add Remote Device.
Scan the phone’s QR code, or paste the phone device ID manually.
Name it clearly, such as Android-Phone or Pixel-Phone.
Save.

Back on the phone, accept the connection request.

At this point, the two devices trust each other, but no folder is synced yet.

Step 3: Receive a Folder Shared from NAS or PC

If the computer or NAS shares a folder with the phone, the phone will show a prompt.

For example:

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Device NAS wants to share folder Notes

Add it, then choose a local path on the phone, such as:

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/storage/emulated/0/SyncData/Notes

After saving, the phone starts downloading from the NAS or computer.

It is better to create the directory manually first so Syncthing-Fork does not place it somewhere unexpected.

If you sync Markdown notes, be careful with application configuration directories. In Obsidian, .obsidian contains workspace state, plugin settings, and cache. If Android and desktop plugins differ a lot, start by syncing only note content and attachments.

Step 4: Back Up Phone Photos to a PC or NAS

The most common phone use case is backing up photos to a NAS or computer.

Photo backup is different from normal file sync. Most people want new phone photos copied to the NAS, not phone deletions mirrored to the NAS. Treat it as one-way backup.

Recommended combination:

Phone side: Send Only
PC or NAS side: Receive Only

The phone sends photos, and the NAS receives and stores them. Add NAS-side file versioning or snapshots to reduce deletion risk.

Add the Camera Folder on the Phone

In Syncthing-Fork’s folder page:

Tap +.
Create a folder.
Use a clear label such as Pixel_Photos or Huawei_DCIM.
Choose the phone’s camera directory.
Share it with your PC or NAS.

The common Android camera path is:

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/storage/emulated/0/DCIM/Camera

Screenshots, WeChat images, or other app images often live elsewhere. Add separate folders when needed:

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/storage/emulated/0/Pictures/Screenshots
/storage/emulated/0/Pictures/WeiXin

Paths vary by Android version, vendor, and app. Confirm with a file manager first.

Set the Phone Folder to Send Only

In the phone-side folder settings, change the folder type from:

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Send & Receive

to:

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Send Only

This makes the phone the photo source. New photos are sent to the NAS, but NAS-side changes are not written back to the phone.

Syncthing is still a sync tool, not a complete backup system. For a safer setup, also enable NAS-side versioning, snapshots, or independent backups.

Configure the Receiver Path

After saving on the phone, the PC or NAS Web GUI will show a prompt:

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Device Pixel-Phone wants to share folder Pixel_Photos

Add it and choose the local storage path.

On Windows:

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D:\Backups\Phone_Photos

On Linux or NAS:

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/volume1/photos/phone

With Docker, remember to use the container path. If the host mapping is:

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- /volume1/photos:/var/syncthing/photos

then the Web GUI path should be:

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/var/syncthing/photos/phone

Set the Receiver to Receive Only

On the PC or NAS, set the folder type to:

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Receive Only

The receiver will accept photos from the phone but will not send local changes back.

This is an extra layer of protection. Even if you move, edit, or delete files on the NAS, those actions should not directly affect the originals on the phone.

Still, Receive Only is not a replacement for NAS history. Enable file versioning or snapshots on the NAS if the photos matter.

Test with a Small Set First

Do not start by syncing tens of thousands of photos.

Test first:

Put 3-5 temporary photos in the phone album.
Confirm that the PC or NAS receives them.
Add a new photo and see whether it syncs.
Delete one test photo on the phone and observe the NAS behavior.
Only then enable the full album.

Folder type and deletion behavior are easy to misunderstand. A small test avoids expensive cleanup later.

Run Conditions: Avoid Mobile Data Usage

Syncthing-Fork run conditions are very useful on Android.

At minimum, enable:

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Run only when connected to Wi-Fi

This avoids syncing large files over 5G or 4G.

If you only want sync at home, restrict it to a specific Wi-Fi SSID. This is useful when the NAS is only reachable on your home LAN.

Charging-Only Sync

If you do not need real-time sync, enable:

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Run only while charging

A stable workflow:

Take photos and write notes during the day.
Syncthing-Fork does not keep running constantly.
At night, return home and connect to home Wi-Fi.
Plug in the charger.
Syncthing-Fork starts and syncs the day’s photos and files to the NAS.

This saves battery and fits phone usage better than always-on sync.

For notes that must update quickly, you can skip charging-only mode and keep Wi-Fi-only mode.

Android 11+ Storage Restrictions

Android 11 and later restrict storage more heavily. Some directories may not be reliably accessible, especially:

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Android/data
Android/obb

SD card directories may also be limited depending on vendor, Android version, and file picker authorization.

Recommendations:

Create dedicated sync directories under internal storage.
Do not use app-private system directories as primary sync folders.
For photos, prefer ordinary media folders such as DCIM/Camera.
For notes, use a clear path such as /storage/emulated/0/SyncData/Notes.

Stability matters more than choosing a path that looks native.

Do not sync all of:

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/storage/emulated/0

It is too large and mixed, with caches, downloads, app data, and temporary files.

Choosing Folder Types on the Phone

Different scenarios need different folder types.

Two-Way Note Sync

If both phone and PC edit the same Markdown notes:

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Send & Receive

Avoid editing the same file on multiple devices at the same time.

Phone Photos to NAS

If the phone mainly sends photos:

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Send Only

Use versioning or snapshots on the NAS.

Read-Only Materials on the Phone

If the phone only needs to read files from the NAS:

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Receive Only

This works for ebooks, reference documents, or script examples.

Think Through Deletion Semantics

Will deleting a phone photo delete it on the NAS? It depends on folder types and sync state.

To reduce risk:

Use Send Only on the phone.
Use Receive Only on the NAS.
Enable file versioning on the NAS.
Add snapshots or separate backups.

If your real goal is archival storage, sync into an inbox directory first, then let a NAS task copy files into an archive directory that Syncthing no longer manages.

Example:

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/volume1/photos/inbox-phone
/volume1/photos/archive

Syncthing writes to inbox-phone; a scheduled script organizes files into archive.

Common Problems

Sync Stops After Screen Lock

Check:

Battery optimization allowlist.
Background running permission.
Auto-start permission.
Whether Wi-Fi-only or charging-only conditions are active.

Often the issue is Android background management, not Syncthing itself.

Cannot Find the Camera Folder

Use a file manager to confirm the real path. The common path is:

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/storage/emulated/0/DCIM/Camera

Third-party camera or editing apps may use other folders.

Sync Is Slow

Check:

Whether the phone and NAS are on the same Wi-Fi.
Whether traffic is going through relay.
Whether 22000/TCP and 22000/UDP are reachable on the NAS.
Whether the phone is in power-saving mode.
Whether there are many small files.

Many small files are slower than fewer large files. After the first sync, incremental sync is usually much lighter.

Deleting Phone Photos Also Deletes NAS Copies

That means your sync relationship is propagating deletions. Syncthing is a sync tool, not a built-in append-only backup tool.

Fixes:

Check folder types on phone and NAS.
Enable NAS-side file versioning.
Add snapshots or independent backups.
Use an inbox directory and archive files outside Syncthing’s control if needed.

Recommended Setup

For Android + NAS:

Install Syncthing-Fork on the phone.
Grant file access.
Add it to the battery optimization allowlist.
Pair phone and NAS.
Put notes under /storage/emulated/0/SyncData/Notes.
Use /storage/emulated/0/DCIM/Camera for photos.
Set the phone photo folder to Send Only.
Set the NAS photo folder to Receive Only.
Enable home Wi-Fi-only sync.
If real-time sync is not needed, enable charging-only sync.
Enable NAS-side versioning or snapshots.

This avoids constant battery drain while still backing up photos when the phone returns home and charges.

Summary

Using Syncthing on Android is not just about installing the app. The important parts are permissions, background behavior, battery settings, and network conditions.

Syncthing-Fork is better suited to long-term phone sync. It can limit sync to Wi-Fi, selected Wi-Fi networks, or charging state, reducing battery drain and mobile data usage.

For photo backup to a NAS, use a one-way backup mindset: phone Send Only, PC or NAS Receive Only, plus NAS-side versioning, snapshots, and independent backups. Syncthing handles transfer; long-term safety still depends on your backup strategy.