• Copying files via USB from my android phone to the PC with Ubuntu is easy, connect the phone directly to the PC via USB. As already mentioned by yehtetmaungmaung, in the phone you must allow it (in a popup window).

  

  I do this often in order to copy photos to the PC, and I use two windows of the file browser 'Files' alias nautilus for this purpose, one viewing the source directory in the phone and one viewing the target directory in the PC).

• Copying files directly via USB from the PC to my android phone does not work. It is 'not allowed'. I have not looked into the details, because I would seldom need it. (I guess the security/privacy settings of my phone are preventing it.)

  But there are workarounds to copy from the PC to the android phone:

  • Email: I can attach files that I send to myself via email (and download those files into the phone).

    

  • Pendrive: I have a USB pendrive with a standard type A connector in one end and a type C connector in the other end.

    

    With an MSDOS partition table and a FAT32 or exFAT file system I can transfer files in both directions (to and from the android phone). But it is a two-step operation.

    Learn how to unmount the file system in the USB pendrive from the phone, particularly important after writing to the USB pendrive. The menu system may vary between android versions, but this link should be helpful, even if it does not match exactly for your phone.

    To safely remove a USB device from your Samsung tablet, follow these steps:

    1. Tap the Apps icon on the home screen.
    2. Tap Settings.
    3. Tap the Device tab.
    4. Tap Storage.
    5. Tap the USB device you want to remove.
    6. Tap the Eject icon.
    7. Tap OK to confirm.

    Your USB device should now be safely removed from your Samsung tablet.

    • First plug the USB pendrive to one device (for example the PC) and copy the files to the USB device. Unmount it (to avoid corruption of the files), and unplug it.

    • Next plug the USB pendrive to the other device (for example the phone) and copy the files from the USB device. Unmount it (to avoid corruption of the files), and unplug it.

Edit 1:

• I tested some settings in my android phone (in the pulldown menu when connected to my computer). I let

  • the phone control USB
  • use USB to transfer files

  

• I also tested with Windows, where I could both read and write. In Windows I found no way to 'unplug safely' alias eject alias unmount the partitions on the phone (built-in drive and card), so I shut down Windows. I have Fast Startup (semi-hibernation) turned off in my Windows system, so it flushes the buffers in the shutdown process.

Going back to Ubuntu, suddenly I could both read and write. I am not sure what happened.

• Maybe the 'dirty' bit was set, and it was cleared after the visit to Windows with the proper shutdown. It is well known that a dirty bit makes Ubuntu unwilling to write to a file system, and it can be fixed by Windows

  • reboot (always)
  • shutdown (only when Fast Startup is switched off).

• Maybe the modified settings in the pulldown menu of the phone made the difference.

• Maybe both of the above actions made copying to the phone (writing in the phone) work.

I am inclined to blame the 'dirty bit', but need more testing to really know how to fix the problem. Finally, I must agree that it should be easier to write to a phone via USB cable from Ubuntu.

Edit 2:

Here are a couple of tips, that can be useful if you want to do 'more' than what your standard tools can manage.

• The command line tool gio can be useful, if/when some standard commands do not work, for example

  gio mount ...
  gio copy ...
  

  See man gio for details.

• In the current Ubuntu versions (2023-2024), for example 22.04.3 LTS, when the phone is connected via USB (and mounted automatically), I find the path to it using this command,

  find /run/user/*/gvfs -maxdepth 1 -name 'mtp:*'