How can I see the temp files that Vacuum creates in SQLite while running

Question

I've read the information about where SQLite puts the temp files while vacuuming (https://sqlite.org/tempfiles.html), but I can't find the file while vacuum is running. I looked in SQLite source and it appears the temp file name is vacuum_db.*, but a find or locate did not display anything. I also did ls -la on /tmp, /var/tmp and /usr/tmp while the command was running and did not see any new files. There are no environment variables defined, so it should be using one of the above directories. I need to prove that a specific directory is being used so I can tell the server administrator which partition needs more space (when vacuum says the disk is full).