usb_lib/README.rst, usb_lib/tasks/install.yml: Add docs on how to dis…

…able Desktop auto-mount functionality on RPi Desktop; other minor doc cleanup

roles/usb_lib/README.rst

@@ -20,6 +20,9 @@ Technical Details:
 
 * IIAB will generally mount USB sticks / drives 'rw' allowing root to both read and write to them.  In addition, in March 2021 (`PR #2715 <https://github.com/iiab/iiab/pull/2715>`_) Kolibri exports were enabled, by also giving non-root users read and write access to VFAT/FAT32, NTFS and exFAT USB sticks — using ``umask=0000`` (in /etc/usbmount/usbmount.conf) to override the ``umask=0022`` default.  This ``umask=0000`` is also required for students to upload to the teachers's VFAT/FAT32, NTFS and exFAT USB sticks, as introduced in January 2025 (`PR #3875 <https://github.com/iiab/iiab/pull/3875>`_).  If, however, you prefer to restore usbmount's default, set ``usb_lib_writable_sticks: False`` in `/etc/iiab/local_vars.yml <http://FAQ.IIAB.IO/#What_is_local_vars.yml_and_how_do_I_customize_it%3F>`_ — please do this prior to installing IIAB — so you don't have to run: ``cd /opt/iiab/iiab ; ./runrole --reinstall usb_lib``
 
+* If you are using a Desktop install of Raspberry Pi OS (vs Lite, for example) for your IIAB, USB sticks will be mounted twice by default, once by usbmount and once by the desktop. You must disable the auto-mount function in the Desktop in order to use the "Upload to USB" functionality, which allows students to upload their work to your USB stick. To disable the auto-mount function, in the File Manager (pcmanfm), go to Edit → Preferences → Volume Management, and uncheck "Mount removable media automatically when they are inserted". 
+
+
 * Official `usbmount 0.0.22 (2011-08-08) <https://github.com/rbrito/usbmount/tags>`_ documentation:
 
   * https://github.com/hfuchs/usbmount/blob/master/README (2010-08-11)

roles/usb_lib/tasks/install.yml

@@ -7,9 +7,10 @@
 # https://github.com/rbrito/usbmount/blob/master/README.md (2018-08-10)
 # https://github.com/rbrito/usbmount/blob/master/usbmount.conf (2010-04-25)
 
-# usb_lib_writable_sticks (e.g., in /etc/iiab/local_vars.yml) must be set to true in order for non-root users to be able to write to VFAT/FAT32, NTFS and exFAT USB sticks.
-# If you are still not able to write to a mounted USB stick, try unmounting the drive (sudo umount <mountpoint>) and then remount it setting umask to 0000 manually (sudo mount -o umask=0000 <device name> <mountpoint>). 
-
+# The variable, usb_lib_writable_sticks (e.g., in /etc/iiab/local_vars.yml), must be set to true
+# in order for non-root users to be able to write to VFAT/FAT32, NTFS and exFAT USB sticks.
+# If you are still not able to write to a mounted USB stick, try unmounting the drive
+# (sudo umount <mountpoint>) and then remount it setting umask to 0000 manually (sudo mount -o umask=0000 <device name> <mountpoint>).
 
 - name: Record (initial) disk space used
   shell: df -B1 --output=used / | tail -1