Questions[udev](ubuntu)

Five days ago I installed Android Studio on a fully updated Ubuntu 2018.04, used the wizard to create an example app, pressed the "Run" button and it ran perfectly on my Android device connected via USB.

Today, on the same Ubuntu and with the same deviced plugged in, I opened the same project and pressed "Run" again. It now fails:

Launching Application
$ adb push /home/nico/src/ActionBarCompat-Basic/Application/build/outputs/apk/debug/Application-debug.apk /data/local/tmp/com.example.android.actionbarcompat.basic
com.android.ddmlib.AdbCommandRejectedException: insufficient permissions for device: user in plugdev group; are your udev rules wrong?
See [http://developer.android.com/tools/device.html] for more information
Error while Installing APK

I did not knowingly modify any Ubuntu configuration or even update the OS.

What could be the problem?
How to investigate further?

I read the Wikipedia article on /dev/null and was playing around by moving files to /dev/null.

For this I created a test_file and put some contents in it:

$ touch test_file
$ echo "This is written by Aditya" > test_file
$ cat test_file
This is written by Aditya

Thereafter I tried to move the file to /dev/null:

$ mv test_file /dev/null
mv: inter-device move failed: ‘test_file’ to ‘/dev/null’; unable to remove target: Permission denied

Since, this gave me a Permission denied Error; I went ahead and used sudo as I normally do whenever I encounter a Permission denied error.

$ sudo mv test_file /dev/null

The command succeeded and test_file is no longer present in the directory.

However, the Wikipedia article says that it is not possible to recover anything moved to /dev/null and it gives an EOF to any process that tries to read from it. But, I can read from /dev/null:

$ cat /dev/null
This is written by Aditya

What did I do wrong and how do I fix /dev/null back to normal? And why did I encounter Permission denied error in the first place?

I have a luks setup with encrypted partition. And I don't want everyone on my computer to see that I have such partition. Unfortunately it shows up in the nautilus "devices" panel as "Encrypted partition".

Is there a way to prevent it from showing there? I managed to setup authentication with usb key and I don't want the encrypted partition show in the panel.

My Logitech R400 presenter sends the following key codes:

keycode 112 (keysym 0xff55,  Prior) [page up]
keycode 117 (keysym 0xff56,   Next) [page down]
keycode  60 (keysym   0x2e, period)
keycode  71 (keysym 0xffc2,     F5)
keycode   9 (keysym 0xff1b, Escape)

Basically, I want to use this presenter to remotely control Banshee, so I'd like to remap Prior to B, Next to N, and so on.

How can I change the keymap for this device only (as I certainly don't want to remap those key codes globally)?

I have a USB scale, a USB HID. Currently, when it is plugged in, the permissions only allow the superuser to access it. How can I configure udev to let anybody access this device? I have the vendor and product IDs, but I would like to match it based on the HID type instead.

Right now, I'm having trouble finding any existing rule that applies to this (I grepped for "hidraw" in /lib/udev/rules.d and /etc/udev/rules.d, among other things).