Cisco IOU requires a license file named iourc . This is a text file containing a license key linked to the hostname of your VM.
It supports almost all the commands found on physical Cisco 15.x hardware. i86bilinuxadventerprisek9ms1541tantigns3bin
This indicates the image is built for x86 architecture (32-bit) running on a Linux platform. Specifically, this is a Cisco IOU (IOS on Unix/Linux) image. Cisco IOU requires a license file named iourc