The Calibre manual says
Note that on macOS and Linux only a single program can connect to an Android device at a time, so make sure the device is not opened in the OS File manager, or the Android File Transfer utility, etc.
Unfortunately, this is a bit difficult to do, at least under KDE, where Dolphin will not easily relinquish its control over MTP devices. So I thought I'd share the solution I found.
I found a clue here:
https://bbs.archlinux.org/viewtopic.php?id=263186
Quote:
What worked for me is
kill kiod5
|
So I did
Code:
ps aux | grep kiod5
to get the process number, and then
Code:
kill -9 <process number>
Then I reattached the Fire to the USB port and restarted Calibre.
Everything works -- and, since I rarely use a graphical file manager, it has had no effect on my other work.
Your mileage may vary.