There are two modes for each folder connection. Classic sync downloads everything, or only the subfolders you tick. Virtual files mode writes placeholders that download only when an application opens them. On Windows, the decision on which files to keep as placeholders is left to the operating system’s Cloud Files API, which decides on its own based on free disk space and last access time; the user can still pin a file with “Always keep on this device” or release it with “Free up space”. The macOS client is available in two different installers, one classic and the other based on Apple’s File Provider extension, and the Linux client doesn’t support virtual file mode. In “suffix” mode, as opposed to the native API, all placeholders are displayed with a .nextcloud file extension.
What happens when both sides change the same file?
Nextcloud Desktop keeps the server copy, renames the local copy to “conflicted copy” and provides a right-click item, “Resolve conflict”, that opens a window where you select which copy to keep. Conflicts can occur even when both copies are identical, since Nextcloud Desktop compares modification metadata, and on Windows a read-only attribute on the file was enough to cause conflicts repeatedly until the attribute was removed. One open bug report mentions the resolve window being dismissed at the same time Nextcloud Desktop crashes.
Why is a file not removed from “Pending synchronization” when “Free up space” is performed?
A documented case: a text file cannot return to placeholder state. “Free up space” leaves it at “Pending synchronization” indefinitely, although it synced fine and is visible in the web interface. Deleting the text so that the file is empty frees it up again. This was reported by a Nextcloud maintainer who was able to reproduce the behaviour.
What is the hidden .sync database in the folder root?
There is a hidden .sync_xxxxxxx.db file in each synced folder root, an SQLite database of what has changed and when. The official troubleshooting guide states that if Nextcloud Desktop gets stuck at “Preparing for sync” or “CSync unknown error”, you stop the client, delete or rename that file and restart it; Nextcloud Desktop rescans all files but only transfers real differences. The cost: the rebuild does not remember which folders you had excluded from downloading, and one user who got out of a stall this way saw two dozen phantom conflicts appear in files no one had touched.
How to exclude a pattern of files from syncing?
Settings -> General -> “Edit Ignored Files” modifies the .sync-exclude.lst file, and a pattern such as */.obsidian/workspace.json excludes just that file. However, a long open bug report mentions that Nextcloud Desktop sometimes ignores its own ignore list, and that files matching the patterns still got uploaded, sometimes 12 or more hours after the ignore list started to work.
What is the restriction on an upload?
Nextcloud Desktop uploads in chunks and sizes them dynamically, aiming for roughly one minute per chunk, with a minimum of 1 MB and a configurable maximum. Behind Cloudflare that limit has to be lower than 100 MB, since Cloudflare slices larger chunks and the sync fails with “Connection closed”. Two additional hard rules from the official manual: pointing Nextcloud Desktop at a folder already synced by another tool such as Dropbox, rsync or Unison risks data loss, and the macOS client refuses outright to connect to servers with self-signed certificates, because App Transport Security blocks the connection before Nextcloud Desktop sees it.
