After connecting the tablet (Samsung Galaxy Tab A) to the computer (Linux Debian 8 - KDE) with the supplied cable, a message popped-up listing the available devices, with first one Portable Media Player and second one Samsung Android. I tried to open both of them and both time after opening with file manager (Dolphin) and clicking on the only listed folder "Samsung Galaxy Models (MTP)" I got the following message: "Could not read. Reason: Could not claim the USB device". I tried with LXDE (instead of KDE) and I could actually read the tablet but not open the files, I could copy from the tablet but the files would be corrupted, and I could copy to the tablet files correctly. Any ideas how can I copy to and from the tablet files OK?

Check to see if your Android device has a setting for USB debug mode. Turn that on prior to plugging it in. Then, see if it has an app/utility for connecting your tablet as a mass storage device.

If that fails,... Use Dolphin to make your Public directory readable as a SAMBA drive. Use a file manager in Android with SAMBA support (like ES File Explorer) to look for network devices and connect to the Ubuntu machine's Public partition that way.