def _yum():
    '''
    Determine package manager name (yum or dnf),
    depending on the system version.
    '''
    contextkey = 'yum_bin'
    if contextkey not in __context__:
        if ('fedora' in __grains__['os'].lower()
           and int(__grains__['osrelease']) >= 22):
            __context__[contextkey] = 'dnf'
        elif 'photon' in __grains__['os'].lower():
            __context__[contextkey] = 'tdnf'
        else:
            __context__[contextkey] = 'yum'
    return __context__[contextkey]