I’m attempting to format an SD card which has been in an Android phone on a previous occasion. It is therefore formatted as exfat. It is mounted as /dev/sdb and I can view files on it.
I want to wipe it and format it as ext4; but none of the typical methods seem to work.
Parted and Gparted operations succeed but once the SD card is re-mounted it is still exfat and the Android files remain on it.
Gnome-disk-utility does not succeed, but instead returns 'error synchronizing after initial wipe: Timed out waiting for object (udisks-error-quark, 0).
Gnome Disks normally shows mounted and unmounted disks I think, in which case you can choose to unmount them or whatever. I wonder if logging out and then logging back in as root may give the OP more options. Otherwise using some kind of rescue disk that you boot from? Apparently SD cards have a switch on them that enables write on/off. I’m not sure about this option however, I can’t test that.
You might want to try putting it back into the Android device and see if you can delete files and format the SD card there. Just for the sake of testing.
If it is successful, you could put it back into your Linux box and see if you can perform any disk manipulation there.