Error with mkdocs serve

[gitressa]

I followed the steps on https://sourcefoundry.org/cinder/ but when I try to serve, I get an error ...

• Ubuntu 20.04
• Python 3.8.10

$ mkdocs serve
INFO     -  Building documentation...
INFO     -  Cleaning site directory
ERROR    -  Error building page 'index.md': main.html
Traceback (most recent call last):
  File "/home/user/.local/bin/mkdocs", line 8, in <module>
    sys.exit(cli())
  File "/home/user/.local/lib/python3.8/site-packages/click/core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "/home/user/.local/lib/python3.8/site-packages/click/core.py", line 1055, in main
    rv = self.invoke(ctx)
  File "/home/user/.local/lib/python3.8/site-packages/click/core.py", line 1657, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/user/.local/lib/python3.8/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/user/.local/lib/python3.8/site-packages/click/core.py", line 760, in invoke
    return __callback(*args, **kwargs)
  File "/home/user/.local/lib/python3.8/site-packages/mkdocs/__main__.py", line 181, in serve_command
    serve.serve(dev_addr=dev_addr, livereload=livereload, watch=watch, **kwargs)
  File "/home/user/.local/lib/python3.8/site-packages/mkdocs/commands/serve.py", line 63, in serve
    config = builder()
  File "/home/user/.local/lib/python3.8/site-packages/mkdocs/commands/serve.py", line 58, in builder
    build(config, live_server=live_server, dirty=dirty)
  File "/home/user/.local/lib/python3.8/site-packages/mkdocs/commands/build.py", line 314, in build
    _build_page(file.page, config, doc_files, nav, env, dirty)
  File "/home/user/.local/lib/python3.8/site-packages/mkdocs/commands/build.py", line 209, in _build_page
    template = env.get_template('main.html')
  File "/home/user/.local/lib/python3.8/site-packages/jinja2/environment.py", line 1000, in get_template
    return self._load_template(name, globals)
  File "/home/user/.local/lib/python3.8/site-packages/jinja2/environment.py", line 959, in _load_template
    template = self.loader.load(self, name, self.make_globals(globals))
  File "/home/user/.local/lib/python3.8/site-packages/jinja2/loaders.py", line 126, in load
    source, filename, uptodate = self.get_source(environment, name)
  File "/home/user/.local/lib/python3.8/site-packages/jinja2/loaders.py", line 218, in get_source
    raise TemplateNotFound(template)
jinja2.exceptions.TemplateNotFound: main.html