Retrosmc

First log into your osmc installation via ssh:

$ ssh osmc@your.device.ip.here

password hint: osmc

Go to the Power menu in Kodi and choose "Quit". This will stop the media center and free up even more resources. Log back in via ssh, as above. Download the installer:

$ wget https://halckemy.s3.amazonaws.com/uploads/attachments/214799/install-retrosmc.sh

After downloading, make it executable and run the script:

$ chmod +x install-retrosmc.sh
$ ./install-retrosmc.sh

You will eventually arrive at a screen to install Retropie. Go ahead and select the install option. The installer should mention that the user osmc isn't part of the input group; agree to add it.