CoreOS quickstart

Today I have tried coreOS inside vmware player and it has been pretty easy. So now I’m ready to share the steps I have followed:


Downloading OVA

OVA file can be imported in both vmware and virtualbox:

curl -LO

Creating the config-drive

We have to created the file user_data with the following yaml content, changing ssh-rsa line with our own public key:


# include one or more SSH public keys
  - ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDGdByTgSVHq.......
    # generate a new token for each unique cluster from
    # specify the initial size of your cluster with ?size=X
    advertise-client-urls: http://$private_ipv4:2379,http://$private_ipv4:4001
    initial-advertise-peer-urls: http://$private_ipv4:2380
    # listen on both the official ports and the legacy ports
    # legacy ports can be omitted if your application doesn't depend on them
    listen-peer-urls: http://$private_ipv4:2380
    - name: etcd2.service
      command: start
    - name: fleet.service
      command: start

Now we are going to create configdrive.iso with the user_data file inside:

mkdir -p /tmp/new-drive/openstack/latest
cp user_data /tmp/new-drive/openstack/latest/user_data
mkisofs -R -V config-2 -o configdrive.iso /tmp/new-drive
rm -r /tmp/new-drive

In the case you are using windows 10, you can open a bash for windows, and install genisoimage:

sudo apt-get install genisoimage

Attach the ISO as a DVD

After that it is enough to attach the ISO file that we have just created to the virtual machine and start it. CoreOS will detect it and we will be able to log-in with the user core using our own private key. CoreOS doesn’t have a default password, so this is mandatory.


ssh core@


CoreOS has a very limited functionality included in its core. That’s ideal for performance and security.

  • We have some tools available from the beginning: docker, git, wget, curl, vi.
  • But we don’t have: nano, gcc, php, python, ruby, svn, or other tools.

In order to access advanced functionality, coreOS offers the tool /bin/toolbox that starts a container with fedora mounting the main file system in /media/root. In this fedora we can install whatever we want: starting with nano, gcc or php.  And in the case we need to access our main filesystem, we have it mounted as /media/root.