One of our Ubuntu 18.04 hosts was caught with 12 GB of
*.journal files, far more than intended. Attempting to find out if they were worth keeping, I ran
journalctl --file $f
on each file older than today; which always resulted in either
Failed to open files or
--- No entries ---.
Am I correct to conclude that such files are junk and can be discarded?
If they are, why do they exist? What is a supported way to clean them up? Is it worthwhile to regularly check systems for their existence?