One way sync (backup to remote system)

Hi, I am pretty sure this thing as already been asked but in fact while trying to find the right information I have not really found my answer so maybe things as changed since then and maybe you could help me on this. So I have store some files and wanted to do a backup on another remote system (like a rpi with a usb disc). I have setup my 2 syncthing as is:

  • source A : send only
  • dest B: receive only

If I add a file to A, it is replicated to B. Cool. If I delete the file in A, then B complain and ask me the cancel the local changes.

But… why? Is there a way to have B just accept the fact that A has delete the file and it’S ok since you only reveive the change?

Is there a special configuration for the one way sync to work witout humnan intervention or this is a feature that make the “one sync backup” a no go for syncthing?

Any information or how-to is welcome. Thanks! R,

The scenario above would only occur if changes were made on “B”, triggering the error warning and option to revert local changes.

Normally “B” would accept all updates from “A” including deletes and not pass any local changes back.

“B” will normally accept deletes from “A” without complaint unless Syncthing’s ignoreDelete feature is enabled.

Syncthing excels at keeping multiple network-connected devices in sync with each other, and although it can be twisted into a backup-like tool, it isn’t what it was designed and/or intended for.

If the goal is to safely back up important files, there are plenty of backup software tools available for free.

Hi and thanks for the reply. So you are right, I use the word backup wrong. I have backups of my stuff using burp backup and it works fine. I just want to test having an online copy of some stuff, as a mirror of some files in case my nas become unuavailable. So in order to check if I was doing something wrong, I have retest from scratch, like cleaning all the config from the source A and destination B. Creating on A a share on a new fodler as send only and adding B as the remote device, then make B accept the share from A as receive only and have it doing some trashcan copy in case of. With a new created share, it works fine, whatever I create a new file or delete it, B sync everything with no complain at all. Now, if I create a new share in A but with an existing folder already containing some files and folders, I got an issue. I have repeated the same process to create the share but after the finaly sync, B still display “Cancel local modifications” (not sure about the exact wording, my instance is in french sorry, but you know what I mean). The local and global state are the same for the files/folder/size. I will let B finish the analyze process and then see if it makes any difference.

Thanks for your comments.

Assumign that the sync modes are the same (device “A” is send-only ; device “B” is receive-only), starting with an existing folder on “A” that already contains files/folders and on “B” the destination folder isn’t empty, Syncthing will display an error and offer the option to revert local changes because it will not merge the preexisting folders on “A” and “B”.

Or in other words, you must decide whether to overwrite whatever is on “B” so that Syncthing can match it up with “A” by clicking the “Revert local changes” button. If a file/folder on “B” doesn’t exist on “A”, it will be deleted, and any files on “B” will be replaced with overlapping files from “A” regardless of if they are newer or not.

I think it has already been answered. I can give you my experience.

When you start the one way synchronization the folder in B must be ‘empty’. Any existing file in B may differ from the original in A. And the syncthing message is correct.

If you’re doing it this way, and the message on B keeps appearing, it’s simple: Device B alters your files, at least in date.

Hi, Thanks for the reply :slight_smile: Yes I am thinking the same so I have tried to change the B (destination) configuration a bit. Right now B is a a RPI4 connected to a external USB disk. The thing is that the external HD was formated with NTFS. Since I am a real lazy person, I have not formated it to something else. Right now, I have just mounted the drive with the default options.

In order to see if it makes any differentce, I now mount the disk with those options:

/dev/sda1 /media ntfs permissions,noatime 0 2

I have started a sync from scratch (meaning cleaning the B folder before adding it again). Let’s see if this resolve the issue.


Hi, Just to update the thread, the mount option on the external USB disk formated in NTFS on a RPI4 seems to have fixed my issue, no more out of sync warning and delete operations work as expected. Thanks!

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