'Folder ID must be unique' error

I am trying to sync two folders from one instance of syncthing, the first folder is ‘Comics’ on my local machine and the other is ‘Comics’ on my NAS.

Local: C:\Comics Remote: Z:\Comics

When trying to set this up, I am attempting to set the remote folder’s ID to the local so they match, although I am getting the aforementioned error. Is what I am trying to accomplish possible with syncthing?


It is possible to create a shared folders with a folder ID of “Comics.” Have noticed that if have ever used a folder ID previously a database sometimes gives some trouble when using it again. For example had a folder where the global file count was off. Tried removing folder and readding but the issue came back. Created a new share (with a new folder ID) and the issue was solved.

Are you sharing the folder (with folder ID “Comics”) from one machine and then clicking “add/ accept” or are you manually adding the folder ID “Comics” on both machines? Which ever way you are doing try the other way around.

Secondarily it may be easier to try again and use a random folder ID and just set the folder name to “Comics.”

An absolute sure way to make the folder ID “Comics” work is to delete the Syncthing database and re-add the folder you want to share with the folder ID of “Comics.” If you do this of course all Syncthing data will be lost so be careful with this.

The remote ‘machine’ is an external hard drive connected to my router which I have mapped as a network drive. I thought I could use syncthing to sync back and forth but I don’t think it’s possible in this sense.

Understood. You are trying to use Syncthing for “local” sync on your machine. That won’t work. However if you want to keep the setup as is Syncthing can run on a router if you can put custom firmware on it to gain SSH access.

A much easier solution is using this for local sync on Windows: https://freefilesync.org/

If you ever try Linux there is a solution called “rsync” that handles local sync.

I’ve looked in to DD-WRT but I don’t think it’s 100% compatible with my router. The installation looks a bit complicated, anyway. Don’t want to brick the router.

I’ll look into those programs you mentioned, though. The NAS is not super critical, I was just want to be extra redundant. :stuck_out_tongue: I already have synthing syncing my local machine onto a cloud server.


Completely agree. Would not spend time putting firmware on the router. But if do Tomato is preferable to DD-WRT.

You only need one folder with that id, so I am not sure why you are trying to add a second one with the same id.

@skarz was trying to use Syncthing for local backup. Hence the desire to create two folders with same ID on the same machine.

Apparently the thread moved alot since I started replying.

Just a thought, what constitutes a local backup? A local backup includes two different physical mediums connected by a network if only one machine is the ‘catalyst’ correct?

local means no network. E.g. on Windows just from C:\ to F:\. Syncthing is for network sync. If you want to sync a dir from internal drive to external drive, you wold need two running syncthings on that PC, each pointing the same folder id to either the internal or the external drive.

Wait, it’s possible to run two instances of syncthing? Wouldn’t that cause a conflict with the machine ID?

You can use the -home parameter to set different home dirs, so the config and DB are separate.

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