As you may know .NRG is the default output format of the Nero software. If you want to convert the .Nrg file to .ISO, then you can give a try to nrg2iso. It is a command line tool to extract the ISO9660 CD image data from Nero “.nrg” files. Even it shows the progress bar while conversion.
Install nrg2iso On Ubuntu / Linux Mint
nrg2iso is available in the Ubuntu universe repository. To install it On Ubuntu and its derivatives, enter the following command from your Terminal:
$ sudo apt-get install nrg2iso
Usage is pretty simple. The default syntax is:
$ nrg2iso <nrg-file> <iso-file>
--help Display the help screen. --version Display the version
The .nrg file will be converted to .iso and saved in the current directory.