My Syncthing cluster has three Devices. The mid-spec Mac and high-spec Win11 machines migrated themselves without my intervention. The mid-spec Win11 machine fails with this error:
I am confident that I can fix this without the forum’s assistance by either renaming syncthing.exe.old, or deleting it.
Is there any value to the Syncthing team in my performing more troubleshooting than this? I’ve been running Syncthing on this machine since v1.27.9 (as you can see) and every other upgrade has been perfectly smooth across all three Devices.
Syncthing runs on Startup using Task Scheduler. The process is running as user “chaos” which has full Administrator rights; the “Run with highest privileges” box is checked in Task Scheduler. The C: volume is on an 1TB SSD and has over 400GB of free disk. The high-spec Win11 machine is set up identically and did not have this issue.
TL;DR: I don’t know why things are working now, but I’m happy they are.
I decided to try to fix it myself – and to my surprise, I could not delete syncthing.exe.old normally. Explorer on Win11 told me that Syncthing had the file open.
Next I stopped Syncthing, deleted the file, and restarted Syncthing. Now I’m seeing these log entries:
2025-09-09 08:33:59 INF Connected to device with a newer version; checking for upgrades (device=KMPNVYY-REDACTED ourVersion=v2.0.7 theirVersion=v2.0.8 log.pkg=main)2025-09-09 08:33:59 INF Automatic upgrade (current=v2.0.7 latest=v2.0.8 log.pkg=main)2025-09-09 08:33:59 ERR Automatic upgrade failed (error=“open C:\Program Files\syncthing-windows-amd64-v1.27.9\syncthing2795135987: Access is denied.” log.pkg=main)
Turns out I stopped Syncthing to look over the log. I restarted Syncthing on the same Device, and of course it automatically upgraded successfully, all Remote Devices and Folders show Up To Date, and files are syncing as expected. I’ll be darned if I know what happened here – I will do a full offline chkdsk next – but Syncthing is working.
