DirAvailableCheck checks if the given directory either does not exist, or is empty.

FileAvailableCheck checks that the given file does not already exist.

HostnameCheck checks if hostname match dns sub domain regex.

HttpProxyCheck checks if https connection to specific host is going to be done directly or over proxy.

InPathChecks checks if the given executable is present in the path.

IsRootCheck verifies user is root.

PortOpenCheck ensures the given port is available for use.

ServiceCheck verifies that the given service is enabled and active.

PreFlightCheck validates the state of the system to ensure kubeadm will be successful as often as possilble.