Is there any way to install Nano on CoreOS?

To do this on a CoreOS box, following the hints from the guide here:

1. Boot up the CoreOS box and connect as the core user
2. Run the /bin/toolbox command to enter the stock Fedora container.
3. Install any software you need. To install nano in this case, it would be as simple as doing a dnf -y install nano (dnf has replaced yum)
4. Use nano to edit files. "But wait -- I'm in a container!" Don't worry -- the host's file system is mounted at /media/root when inside the container. So just save a sample text file at /media/root/home/core/test.txt, then exit the container, and finally go list the files in /home/core. Notice your test.txt file?

If any part of this is too cryptic or confusing, please ask follow up questions. :-)

While the Dan's answer is basically correct, it seems that yum isn't working anymore in the latest CoreOS installation (installed yesterday from the latest coreos_production_vmware_ova.ova from http://stable.release.core-os.net/amd64-usr/current into a VMWare Workstation on Windows).

The cited yum command aborts at the end. So replace step (3) with the command

/usr/bin/dnf install nano

which successfully installs nano in the fedora container.

Do your edits with nano inside this fedora container (accessible from CoreOS prompt by /bin/toolbox), while obeying the mounting advise of Dan's post. Leaving the fedora container can be done by the 'exit' command.

There is a simpler option that I found on a reddit post

First connect as the core user and then, make sure /opt/bin exists (sudo mkdir -p /opt/bin) before executing the following command:

docker run -d --name nano base/archlinux:latest sleep && sudo docker cp nano:/usr/bin/nano /opt/bin && docker rm nano

Hopefully /opt/bin is already in the PATH so as soon as it worked, you will have nano available.