I am running Debian 9 via Crouton on an Intel Chromebook. I've had some difficulties with bash and the display, however I resolved these. I installed Steam, and the games work on it, however I only have 16GB on the eMMC chip inside the computer.
I would like to download Steam games on an external SD card. Inside the Chroot, the SD card I have inside the built in slot is mounted in /media which has a symbolic link to /var/host/media/removable/USB (USB being the name of the SD card), however when I try to add it as an extra Steam games location, Steam tells me that the "new Steam library folder must be on a filesystem with execute permissions".
Just to be clear, I am able to read and modify contents on the SD card via the Chroot. How can I make the SD card usable by Steam?