tl;dr version: I have a localdb.kdbx.tmp file on a local network drive that I can't rename/delete/copy/overwrite/open/etc. All attempts, sudo or otherwise, throw a "Device or resource busy" error. Running fuser and lsof shows nothing; as far as I can tell nothing is actively accessing the file and there is no associated PID or parent process. Remounting the drive with FUSE set to allow root and other users makes no difference. File permissions are normal and everything else in the directory (backups etc.) are behaving as expected.
details: I have a KeePass shared database that's hosted on a local network drive shared between several on-site computers. Some of the machines run Windows, some run Linux. I'm personally using 32-bit Ubuntu 14.04 with keepass2 2.34 installed.
When attempting to save some recent updates to the localdb.kdbx KP database yesterday (I was the only person accessing the file at the time), Keepass threw an error and said the database may be corrupted. I shut down my machine, assuming I could overwrite the file the next day. But when I came in and connected to the drive this morning, localdb.kdbx only existed as localdb.kdbx.tmp and no one can get it to open (KeePass specifically throws a "lock violation on path" error).
I'd troubleshoot the issue on KeePass's forums, but we only need to be able to use the filename, so I'd be happy with just deleting it so I can recreate it from a backup. Problem is, I get a "Device or resource busy" error whenever I try to do anything with the file. Using lsof and fuser on the .tmp file just returns a blank with no PID, so there's nothing to kill and no way to "free up" the file for deletion. I thought it might be a FUSE issue and tried the solutions at How to get sudo access to shares mounted by Gigolo and WARNING: can't stat() fuse.gvfsd-fuse file system with no luck.