error while installing ros from source on ubuntu arm

edit

Hello, Although the website provides methods installing ros on arm, it is an armhf version of Ubuntu .However,I use an armel version of Ubuntu.So I want to install ros from source on the armel version of Ubuntu according to this page http://wiki.ros.org/groovy/Installati... When I excute

$ rosinstall_generator ros_comm --rosdistro groovy --deps --wet-only > groovy-ros_comm-wet.rosinstall

there was an error as follows,

Traceback (most recent call last):
  File "/usr/local/bin/rosinstall_generator", line 141, in <module>
    rc = main()
  File "/usr/local/bin/rosinstall_generator", line 129, in main
    upstream_version_tag=args.upstream, upstream_source_version=args.upstream_development)
  File "/usr/local/lib/python2.7/dist-packages/rosinstall_generator/generator.py", line 247, in generate_rosinstall
    wet_package_names, unreleased_repo_names = _get_packages_for_repos(distro_name, repo_names)
  File "/usr/local/lib/python2.7/dist-packages/rosinstall_generator/generator.py", line 93, in _get_packages_for_repos
    wet_distro = get_wet_distro(distro_name)
  File "/usr/local/lib/python2.7/dist-packages/rosinstall_generator/generator.py", line 213, in get_wet_distro
    _wet_distro = _get_wet_distro(distro_name)
  File "/usr/local/lib/python2.7/dist-packages/rosinstall_generator/distro.py", line 45, in get_distro
    return get_cached_distribution(index, distro_name)
  File "/usr/local/lib/python2.7/dist-packages/rosdistro/__init__.py", line 134, in get_cached_distribution
    cache = get_distribution_cache(index, dist_name)
  File "/usr/local/lib/python2.7/dist-packages/rosdistro/__init__.py", line 160, in get_distribution_cache
    yaml_gz_str = load_url(url, skip_decode=True)
  File "/usr/local/lib/python2.7/dist-packages/rosdistro/loader.py", line 59, in load_url
    raise URLError(str(e) + ' (%s)' % url)
urllib2.URLError: <urlopen error <urlopen error [Errno -2] Name or service not known> (http://ros.org/rosdistro/groovy-cache.yaml.gz)>

Please help me slove the problem,thank you very much.