Run the command /opt/unetlab/wrappers/unl_wrapper -a fixpermissions to ensure the file is executable.

Compiled on March 28, 2018, and officially released around May 2018. Software Version: 15.7(3)M2.

Because it runs as a native Linux process, you can launch dozens of instances of this image on a modest computer compared to only a few heavy QEMU-based images. How to Use the Image in Simulators

You must have a valid iourc license file in the same directory for the image to boot. Cisco IOU L3 - GNS3

While primarily a router image, it supports many L3 switching features often needed for CCNP or CCIE lab environments.

Use an SFTP client (like WinSCP) to upload the file to /opt/unetlab/addons/iol/bin/ .