Since the 20180312 TW snapshot Dolphin throws an error when attempting to mount media, claiming:
“An error occurred while accessing ‘Wastebin’; the system responded: The device is already mounted: Device /dev/sd(Xn) is already mounted at ‘/run/media/(user)/(device label)’.”
This happens when attempting to mount any device, external USB, internal (unmounted) drive, no matter what.
Login, Launch Dolphin and insert a USB stick. The USB correctly appears as unmounted in (Dolphin Panel) Devices section, and the Device Notifier plasmoid opens. In Dolphin, click to mount and the following happens:
Additionally, and I don’t know if this previously worked or is related. If instead of attempting to mount the USB from a running instance of Dolphin I select “Open with file manager” from the Device Notifier, that fails with a “Malformed URL” error message.
Looking through the change log for that snapshot, no updates occurred for Dolphin, but there was udisks2 (2.6.5 -> 2.7.6), possibly related?
Well, it’s obviously caused by a change in udisks2 then.
Whether it’s to be considered as bug in udisks2 or KDE Frameworks I cannot tell really.
Apparently KDE Frameworks would need to be adjusted to the latest udisks2, but personally I’d say udisks2 shouldn’t have such incompatible changes in the first place…
I temporarily reverted back to udisks2 2.7.6 and indeed the media is actually mounted, despite the warning.
Insert USB stick
Click to mount - error displayed
Click elsewhere on a “Places” entry (Home, Downloads, whatever)
Re-Click on the USB device - now shown as mounted and Dolphin displays the contents.
There seems to be a general acknowledgement of a problem so hopefully it will be resolved. On this TW system it was definitely the udisks2 2.6.5 -> 2.7.6 update that caused the bug to manifest itself. However in Comment #3 of this https://bugs.kde.org/show_bug.cgi?id=391290 report the problem appears to present itself also with udisks2 2.1.7.
I very frequently need to mount removable media from Dolphin, so for the moment have locked udisks2 at the 2.6.5 version.
As an aside, the udisks2 2.6.5 → 2.7.6 update also pulls in a lot of new dependent packages…