A .nrg file is a proprietary CD image file format used by Nero Burning ROM. In Ubuntu Linux, you can easily convert the .nrg to .iso file using the command line tool nrg2iso.

nrg2iso is available in Ubuntu universe repository. You can install it using Ubuntu Software Center. Or run below command if you’re on Ubuntu Server without GUI:

sudo apt-get update; sudo apt-get install nrg2iso

Once installed, you can convert .NGR file to .ISO via one command. For example:

nrg2iso image.nrg image.iso

That’s it. Enjoy!