manage.py runserver fails with "nodename nor servname provided" when run using an rfc6761 hostname

[Chris Rose]

$ uv run manage.py runserver nomnom.dev.localhost:8441
Watching for file changes with StatReloader
2026-04-03T15:53:16.440737Z [info     ] Watching for file changes with StatReloader [django.utils.autoreload]
Performing system checks...

System check identified no issues (0 silenced).
Error: [Errno 8] nodename nor servname provided, or not known

nomnom.dev.localhost doesn't directly resolve in DNS, but it is a valid RFC 6761 special use domain.

I've attached my settings, and because ALLOWED_HOSTS is relevant, here's that value from manage.py shell:

uv run manage.py shell
45 objects imported automatically (use -v 2 for details).

Python 3.13.12 (main, Feb  3 2026, 17:53:27) [Clang 17.0.0 (clang-1700.6.3.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from django.conf import settings
>>> settings.ALLOWED_HOSTS
['nomnom.dev.localhost']
>>>

[Tim Graham]

​The documentation for runserver says, "You can pass in an IP address and port number explicitly."

There's an example with localhost, but I don't know that hostnames are otherwise supported. Have you looked at the code to identify where you believe Django is at fault?

[Chris Rose]

Nope. I've been utterly unable to get a stack trace to appear. --traceback did nothing for me either.

[Sarah Boyce]

$ python manage.py runserver nomnom.dev.localhost:8441

Watching for file changes with StatReloader
Performing system checks...

System check identified no issues (0 silenced).
April 04, 2026 - 12:04:50
Django version 5.2.9, using settings 'example.settings'
Starting development server at http://nomnom.dev.localhost:8441/
Quit the server with CONTROL-C.

WARNING: This is a development server. Do not use it in a production setting. Use a production WSGI or ASGI server instead.
For more information on production servers see: https://docs.djangoproject.com/en/5.2/howto/deployment/                   

This works for me. So I wonder if this is something to do with your setup, perhaps try running ping nomnom.dev.localhost?

[Chris Rose]

nomnom.dev.localhost does not resolve for me in DNS.

​https://datatracker.ietf.org/doc/html/rfc6761#section-6.3 suggests that it's supposed to resolve to loopback.

$ ping nomnom.dev.localhost
ping: cannot resolve nomnom.dev.localhost: Unknown host
$ dig @ns-59.awsdns-07.com nomnom.dev.localhost
$ dig @8.8.8.8 nomnom.dev.localhost
$ dog @8.8.8.8 nomnom.dev.localhost
Status: NXDomain
SOA  23h59m55s A "a.root-servers.net." "nstld.verisign-grs.com." 2026040400 30m00s 15m00s 7d0h00m00s 1d0h00m00s

From what I can tell, it doesn't resolve anywhere, so I'm not sure what my local setup is going to be doing with it.

At a bare minimum I sure would love it if --traceback would show me where this resolution is happening, so that I can attempt to troubleshoot it in more detail, but I can't get a stack trace out of that command.

[Tim Graham]

It also works on my system (Ubuntu 24.04):

$ ping nomnom.dev.localhost
PING nomnom.dev.localhost (::1) 56 data bytes
64 bytes from ip6-localhost (::1): icmp_seq=1 ttl=64 time=0.038 ms

$ dig nomnom.dev.localhost

; <<>> DiG 9.18.39-0ubuntu0.24.04.3-Ubuntu <<>> nomnom.dev.localhost
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 24028
;; flags: qr aa rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;nomnom.dev.localhost.		IN	A

;; ANSWER SECTION:
nomnom.dev.localhost.	0	IN	A	127.0.0.1

;; Query time: 0 msec
;; SERVER: 127.0.0.53#53(127.0.0.53) (UDP)
;; WHEN: Sat Apr 04 12:36:37 EDT 2026
;; MSG SIZE  rcvd: 65

To see a traceback, edit the except OSError as e: line in django/core/management/runserver.py. Here's an example if I use an invalid hostname:

Traceback (most recent call last):
  File "/usr/lib/python3.12/threading.py", line 1073, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.12/threading.py", line 1010, in run
    self._target(*self._args, **self._kwargs)
  File "/home/tim/code/django/django/utils/autoreload.py", line 83, in wrapper
    raise e
  File "/home/tim/code/django/django/utils/autoreload.py", line 66, in wrapper
    fn(*args, **kwargs)
  File "/home/tim/code/django/django/core/management/commands/runserver.py", line 144, in inner_run
    run(
  File "/home/tim/code/django/django/core/servers/basehttp.py", line 265, in run
    httpd = httpd_cls(server_address, WSGIRequestHandler, ipv6=ipv6)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tim/code/django/django/core/servers/basehttp.py", line 78, in __init__
    super().__init__(*args, **kwargs)
  File "/usr/lib/python3.12/socketserver.py", line 457, in __init__
    self.server_bind()
  File "/usr/lib/python3.12/wsgiref/simple_server.py", line 50, in server_bind
    HTTPServer.server_bind(self)
  File "/usr/lib/python3.12/http/server.py", line 136, in server_bind
    socketserver.TCPServer.server_bind(self)
  File "/usr/lib/python3.12/socketserver.py", line 473, in server_bind
    self.socket.bind(self.server_address)
socket.gaierror: [Errno -2] Name or service not known