Do you have k3b? if not, install it from your linux's package manager.

In k3b, click on Tools > Rip Audio CD
Next, click on Start Ripping
A dialog box will open and at the bottom choose the file type eg. Mp3 ( lame ) and on the right, put a check on Create Single file

lastly, click on Start Ripping.

This should give you what you want. All tracks on one single mp3 file.