Tools > Serial Port option grayed out on linux

I am using an UNO on linux mint. The Serial Port option is grayed out.

I checked using dmesg and the board is connected to /dev/ttyACM0, then I tried running arduino with sudo, but every time I click the tools menu I get this:

java.lang.NullPointerException thrown while loading gnu.io.RXTXCommDriver

also used ls -la /dev/ttyACM0, got this:

crw-rw-rw- 1 root dialout 166, 0 Oct 22 18:01 /dev/ttyACM0

Someone help, I can't seem to find a solution to this case, and there are a lot of things I don't understand in older posts.