Quite some time ago, I used to play audio CDs on my computer while working on other things; when one CD completed, I would eject it, insert another, and continue playing. I recently attempted to do that again after a number of years and discovered that, once I ejected a CD, I could no longer read another until I logged out and back in.

The machine is running Linux Mint 19.1 / Cinnamon 4.0.10 / Kernel 4.15.0-54-generic, and is kept up to date.

When attempting to load a different CD, I receive messages such as:
“Could not display “cdda://sr0/”. The location is not a folder.” or
“Unable to open a folder for Audio Disc. Cache invalid, retry (internally handled)”

Needless to say, this is quite annoying. I attempted several things:
* I tried the same process on a separate machine, which is set up in a similar fashion. Same behavior.
* I tried different methods of ejecting, both mechanical as well as software. Same behavior.
* I completely shut down the Nemo/Files application between attempts. Same behavior.
* I created a subdirectory under /media and added an entry to /etc/fstab using “auto rw,user,noauto,exec,utf8” (which I don’t recall ever having to do in the past). Same behavior.

I realize not many folks use CDs any more, but can anyone help make some sense of this or suggest what I might look for? Thanks.

You don't say what application you're using to play the audio CD's, but if you mount it, it's going to STAY mounted, until you unmount. And trying to eject a volume that's mounted will lead to unexpected behavior. If you're double-clicking through Nemo, it's mounting the disc first, then running your player.

Most dedicated audio CD software will 'just work' with a disc, as long as it can spin the device up.

Thanks, but I'm well aware of the need to unmount removable media before ejecting; I use USB drives extensively as well, which work pretty much the same way. Audio players (and I've tried several) all have their own eject commands, and all of these handle unmounting in the background and have for many years. With all of the players that I'm familiar with, pressing the front panel eject button will do nothing if any player has it mounted. There's been no need for a user to explicitly unmount a CD for years if not decades; unlike thumb drives, a CD is physically "locked" in the tray until it is unmounted, and pop-up messages warn users when that's attempted.

So let me add more about something else I've tried.

After a clean boot, I insert a CD.

When the "What do you want to do?" dialog pops up, I select "do nothing" or "open nemo/nautilus" or whatever. No automatic playing is selected.

At that point, I can see the "read-only" .wav files for the CD that's inserted - using either nemo/nautilus or using ls in a shell (mint uses bash). I don't click on any of these files to play them.

If I use any of the available software methods to "eject" the CD WITHOUT PLAYING IT, I get a message saying it's safe to remove the CD. This clearly indicates that the CD is no longer mounted.

If, on the other hand, I use the front panel eject button after closing nemo/nautilus, the CD ejects; this would not happen if the disk were "busy."

At this point, if I insert a different CD, the "What do you want to do?" dialog pops up correctly; the machine therefore "knows" that a different CD has been inserted. Choosing ANY OPTION at that point will result in one of the messages I quoted in the original post. (And, yes, I do take care to close the shell first; attempting to eject using any method - soft or hard - without first closing the shell or at least changing away from the CD's directory will also - correctly - give an error message saying the CD drive is busy and refuse to eject it.)

This latter experiment indicates (I think) that the issue is not related to audio disks specifically, although the “Unable to open a folder for Audio Disc. Cache invalid, retry (internally handled)” does suggest that the system knows the "new" disk contains audio tracks. The phrasing of the messages suggests the reference is to the drive itself rather than the media; that's why I tried explicitly defining it in fstab as removable but, as I said, that didn't make any difference, and I don't recall needed to ever explicitly do that in the past.

In order to read any CD that's inserted after the first has been ejected (and, by the way, I also confirmed that gparted no longer "sees" it either after it's been ejected), a logout/login sequence is required.

I guess the next thing is to try finding someone with an external USB CD-reader to see how that reacts.

UPDATE: I booted the same computer with a Kubuntu 18.04 ISO and, although slower, it behaved perfectly through several CD changes.

I therefore expect that my issue is related to the Mint/Cinnamon release.

Where should I report this for testing/confirmation/fixing ??

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