I am trying to run Terraria on Ubuntu and running start.sh does nothing.
Running game/Terraria directly gives me:

AL lib: (EE) ALCplaybackOSS_open: Could not open /dev/dsp: No such file or directory

Does anybody know how to fix this?

Two wild guesses.
1: Did you install it outside of /home/$username/GOG Games/?
2: Run a LDD on the Terraria bin files.

There is not a ton of information that you're giving here but... I'm going to assume that you only typed start.sh

Find the file you downloaded for Terraria that ends in .sh (the main download) and open up a terminal in that folder, usually right clicking on an empty space does this. The basic instructions are copy and pasted from Ubuntu help, and it's how I install my GoG games on linux.

How to Execute INSTALL.sh Files in Linux Using Terminal

Download the software you wish to install.
Extract the Tar or Zip to your Desktop.
Double-click the extracted folder.
Open a terminal window.
Type cd ~/path/to/the/extracted/folder and press ↵ Enter.( only if you opened the terminal from the hotbar)
Type chmod +x install.sh and press ↵ Enter. ( 'install.sh' replace the word install with the name of your game.sh)
Type sudo bash install.sh and press ↵ Enter. ( the sudo bash part can be done like this ./nameoffile.sh )
Enter the root password and press ↵ Enter. ( this step may not be required depending on how your OS is setup)

Look inside the game/ directory and see if there is a client-crashlog.txt file.
If so the contents of that should provide more details on the crash terraria is experiencing.







One thing that I can suggest. Is trying setting the TERM environment variable to xterm when running start.sh

e.g. run
TERM=xterm ./start.sh

On my debian machine that fixed terraria crashing for me - in my case the client-crashlog.txt showed a stacktrace reporting System.Console Magic number is wrong: 542
which after some research led to bug reports about some mono versions not working with certain TERM values (my shells were defaulting to xterm-256color).

The problem I hit most likely isn't the same one you are experiencing since I didn't get any messages about /dev/dsp but it seemed worth mentioning since it should take 10 seconds to try running with TERM changed on the off chance it is actually of help here.