def main():
    url = '%s/%s/%s/%s' % (SERVER, PATH, REVISION, FILENAME)

    sysroot = os.path.join(SCRIPT_DIR, os.pardir, 'third_party', 'linux',
                           'sysroot')

    stamp = os.path.join(sysroot, '.stamp')
    if os.path.exists(stamp):
        with open(stamp) as s:
            if s.read() == url:
                return

    print('Installing Debian root image from %s' % url)

    if os.path.isdir(sysroot):
        shutil.rmtree(sysroot)
    os.mkdir(sysroot)
    tarball = os.path.join(sysroot, FILENAME)
    print('Downloading %s' % url)

    for _ in range(3):
        response = urllib.request.urlopen(url)
        with open(tarball, 'wb') as f:
            f.write(response.read())
        break
    else:
        raise Exception('Failed to download %s' % url)

    subprocess.check_call(['tar', 'xf', tarball, '-C', sysroot])

    os.remove(tarball)

    with open(stamp, 'w') as s:
        s.write(url)