If by "Arcade Mode" you mean EmulationStation then:
Pressing F4 will exit EmulationStation and drop you to the Terminal. Or you could use the ES main menu by pressing "Start" and selecting "Quit" and then "Quit EmulationStation".
If you bought a custom premade image then I have no idea what software you're using and only the original seller can help you,
so to run this from emulationstation @mitu said to add XINIT: /opt/retropie/ports/dunelegacy/dunelegacy in the emulators.cfg file in /opt/retropie/configs/ports/dunelegacy folder and retropie's run command will handle xinit. So I removed xserver-xorg-legacy package and tested what he told me to do. It does in fact work, no need for sudo before the xinit command with his suggestion.
As a side note he actually told me to do this for glhexen2 which needs xinit but couldnt find the game data files if you run "sudo xinit". I used what he told me and applied it to dunelegacy.
There are two more issues, one I have overcome the other I need help with. The issue I overcame was that when you run dunelegacy it says it cant find the pak files to run the game and wants them either in the "data" folder or /home/pi/.configs/dunelegacy/data". So in the start script located in /home/pi/Retropie/roms/ports/dunelegacy.sh I added "cd /opt/retropie/ports/dunelegacy" before the runcommand line. This first puts you in the dunelegacy directory with the executable and the data folder it wants, then runs the runcommand to execute the dunelegacy executable. I wish I could have the data under /home/pi/RetroPie/roms/ports like every other game ran in emulationstation but I havent figured out how to do that yet if its even possible.
The issue I need help with is I have no keyboard in dune legacy, but the mouse works. The game works fine otherwise. I cannot figure out how to get the keyboard working.
Keyboard does work in glhexen2 using XINIT: string so it must be something wrong with dunelegacy??
@mitu I had the same issue. It would always ask for a password on first game only. I followed the guides to no avail and found my problem was where in the file I put the user. It must go at the end of the sudoers file after the #includedir line. Once I did that it loaded without asking for permission. I doubled checked by rebooting and running emulationstation again and it loaded as expected. Hope this provides some clarity. This StackExchange thread is where I finally figured out my error.
@project_gamer You messed up the permissions on the /etc/sudoers file. Boot the PI in safe mode and restore the permissions on the file - it should be owned by root and not by the pi user. You probably chown-ed the /etc folder to the pi user :(.
Sorry about that, after entering amixer -i the output is amixer: Mixer default error: No such file or directory and entering amixer -l just gave the above error when I thought you said amixer -1,
And would you have any idea about how I would even read the boot/config.txt file