Understanding 2-way sync plus one way sync

I’m only a semi-technical person (but very concerned about cloud security/privacy), so a response with simple, step-by-step instructions would be very appreciated … I can’t find YouTube or other guides that help with this particular situation, and I’ve been going around in circles trying to get the following set up:

I want to have Device A (my “master” device) sync a folder “Common” with Device B, with two-way read and write. Then, I want to have a Device CCommon” folder synced to that same Device A folder, but only so that Device A could update to Device C, and not the reverse.

(By the way, on Device C, I set the folder to “Receive-only”).

The two-way Device A ↔ Device B sync seems to work, but everything I tried to one-way-sync Device A to Device C seems to end up with “subdirectory” errors, or no sync at all (nothing appears in Device CCommon” folder).

I’m also confused by the “Sharing” tab on the device dialog and the folder dialog, and when to use them. I didn’t seem to need to set those when I set up Devices A and B.

I have feeling that I set up devices/folders/permissions in the wrong order, but I’m not sure. Thanks in advance for any shared wisdom.

Everything you’ve described so far sounds fine and is a pretty common setup.

If I were to guess, I’d say that Device C doesn’t yet share a folder with Device A. Screenshots of Syncthing’s web GUI on Device A and Device C with the “Common” folder panel open so that the sharing details are visible would be most helpful.

(It’s fine to redact parts of the screenshots, but try not to black out too much because it makes diagnosing the issue more difficult – the more details available, the faster the solution.)

Thanks, Gadget, here are some screenshots, with my notes on them. Forgive the blanked-out areas … I’m not sure what is safe to show, but I added descriptions in those cases.

If you can’t see an “Ah-ha” here, I’d be willing to start from scratch, with step-by-step instructions, to create a relationship between Devices as follows: C <— A <—> B with A being Master and C receiving only.

Assuming that the “Common” folder has the same ID (partial visible as “l51” in your screenshots) on all of the devices, the most likely issue is that Syncthing on your Device C Android device doesn’t have permission to display notifications so when Device A attempted to share, the dialog for accepting it on Device C was missed.

Try this…

  1. On Device A, toggle the checkbox off for “Common” under the Shared folders section.
  2. On Device C, in Syncthing, tap the hamburger menu in the upper-left corner and select “Web GUI”.
  3. On Device A, re-enable the sharing to Device C.

Ah ha … I never saw an instruction that it was necessary to open the Web GUI on Syncthing-Fork on Android 9 to accept folder-syncing from my PC. But there it was. Thanks!

Also, I noticed that the Syncthing-Fork app interface doesn’t allow me to initiate a send/receive share on my Android 9 external SD (Device B), but it’s Web GUI does, so I can set the SD for send/receive that way, but the difference in behavior is a mystery to me.

And I resolved the 2-way plus 1-way for "C ← A ← → B: by making the A “Common” folder first and sharing it from A to C and B (essentially, making the PC be the “Master”)

Now, the only problem I’m having is an “Ignore Patterns” issue with a two-way sync for my DCIM folder (android pictures) between my PC (A) and my Android (B):

Because of a large number of camera pictures, and other media, on my Android 9, and it’s more limited internal space, I use the external SD as a default for those. There are over 20 folders on the SD, and I want to sync about half of them.

Handling sync setup on the Android side, using the Syncthing-fork Web GUI, I tried to set up to send-receive my SD root with my PC, using " ! " on the folders I wanted included in Ignore Patterns, followed by a " * ".

When I saved the new folder, the error message I got on the Syncthing-fork Web GUI was: “2024-04-11 17:56:05: Saving .stignore: open /storage/0000-0000/.syncthing.tmp.675901797: permission denied”. Then, when I inspected the folder Ignore Patterns tab, the box was empty. (It will send/receive the SD folder contents but won’t save the .stignore file to the SD???)

In the Android app settings, I set all permissions to allowed for Syncthing-fork (at least, that it displays), and I even enabled “advanced → change system settings”.

The 3 dots menu in the permissions area seems to confirm that the Syncthing-fork app can modify/delete/read SD contents.

I can work around this by creating separate shares for each SD folder that I want, but then I’ll have a clunky-long list of folders on both of my Androids and double that on my PC Syncthing GUI !

Maybe this is some Android 9 (or Samsung) quirk but, more likely, I’m just too new to this app.

I’d appreciate thoughts from you or anyone else out there.

Thanks again for your previous help.

PS, I just checked my Android 14 device, and it doesn’t have trouble saving the .stignore folder to SD. So if anyone knows a workaround for my Android 9 …

Synching officially supports SD cards only in Android 11 and newer (and Android 4.3 and older, but the current app no longer works on those).

I’ve seen at least a few reports on the forum where people mentioned SD card sync working in other Android released, however, as you can see, the end result can be very flaky.

You may try experimenting with running Syncthing as root, but if that doesn’t work, then there’s likely nothing that can be done about it :slightly_frowning_face:.

Ooof. I was trying to squeeze some more life out of my Android 9 phone, but now I’ll have to consider a switch to a new device. Until then, I’ll have to fall back on my SFTP. Filezilla will enable a highlighted folder comparison to highlight unmatched timestamps but, still, the process is manual.

I wonder if there’s a (free) way to automate that?

And I’m just wondering what new problems would arrive if I switched to a newer device … the SD card, on that, may then be accessible by Syncthing, but other of the apps I have (about 225 !!!) might fail. I know Google keeps trying to tighten up Android.

Anyway, thanks, gadget and tomaz86, for your replies.

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