def install_salt_support(from_ppa=True):
    """Installs the salt-minion helper for machine state.

    By default the salt-minion package is installed from
    the saltstack PPA. If from_ppa is False you must ensure
    that the salt-minion package is available in the apt cache.
    """
    if from_ppa:
        subprocess.check_call([
            '/usr/bin/add-apt-repository',
            '--yes',
            'ppa:saltstack/salt',
        ])
        subprocess.check_call(['/usr/bin/apt-get', 'update'])
    # We install salt-common as salt-minion would run the salt-minion
    # daemon.
    charmhelpers.fetch.apt_install('salt-common')