Description of problem:

After upgrading from Foreman 1.19 to Foreman 1.20, RancherOS provisioning is not possible.

Unable to render PXELinux template ‘PXE RancherOS’: wrong number of arguments (given 1, expected 2…3)
Fetch TFTP boot files for pxetest.container.domain.de task failed with the following error: wrong number of arguments (given 1, expected 2…3)

How reproducible:

Upgrade Foreman from 1.19 to 1.20 and try to provision RancherOS.

Workaround:

Comment out /usr/share/foreman/app/models/operatingsystems/rancheros.rb

  def boot_files_uri(medium, architecture, host = nil)
    super(medium, architecture, host)
  end