How to download files from your Android smartphone to your Linux system:
See the answer by Sullivan answered Nov 29, 2016 at 12:21 at
https://askubuntu.com/a/854936
Ie. install the package "
jmtpfs", then create a mount directory (for example /mnt/myphone ),
then mount the device by issuing "jmtpfs /mnt/myphone", then use normal file operations on your Linux:
for example list a tree view of the device that shows all the files, then download (ie. copy) the file(s) you want.
Of course uploading files to the smartphone works as well.
Afterwards unmount the the device, as is usual with such external file storages like USB sticks.
Update: on my device (Android 9) each time I have to enable (activate) "Developer options" under Settings, and then therein enable (activate) "USB debugging".
When connecting the USB cable a notification on the smartphone is generated; one has to tap on it and then a big menu pops up, there one has to select "Use USB for File transfers...
MTP... etc" (Media Transfer Protocol). Now you can issue the above said mount command on the Linux system...
By this method one of course can make also a backup of all user files, though the Android system has also special functions for making complete backups incl. the Android system itself and its cfg files etc. ie. a complete backup.
