We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
404 on single user notebook server anytime I restart jupyterhub
I just deployed jupyterhub from scratch using my ansible scripts this morning. The script are unchanged from 2-3 weeks ago when I did it previously and it was all working. I am running from latest master of jupyterhub.

Anytime I restart jupyterhub (hub+proxy) I see the following behavior:
- I can log in (using GitHub OAuth)
- Trying to start my server gives me a 404 on `/hub/users/ellisonbg`. I can tell from the server log that the single user server isn't being started.
- I can go to the Admin page and start my server from there.
- But then, I get a redirect loop when I try to go to my single user server.
- If I clear all my cookies while my single user server (started through the Admin page) is still running, it starts to work as expected. I can start and stop the single user server on the control panel page just fine.
- If a restart jupyterhub, the problems start all over again.

I am using a fixed proxy_auth_token and cookie secret.


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `jupyterhub/handlers/pages.py`
Content:
```
1 """Basic html-rendering handlers."""
2 
3 # Copyright (c) Jupyter Development Team.
4 # Distributed under the terms of the Modified BSD License.
5 
6 from tornado import web, gen
7 
8 from .. import orm
9 from ..utils import admin_only, url_path_join
10 from .base import BaseHandler
11 from .login import LoginHandler
12 
13 
14 class RootHandler(BaseHandler):
15     """Render the Hub root page.
16     
17     If logged in, redirects to:
18     
19     - single-user server if running
20     - hub home, otherwise
21     
22     Otherwise, renders login page.
23     """
24     def get(self):
25         user = self.get_current_user()
26         if user:
27             if user.running:
28                 url = user.server.base_url
29                 self.log.debug("User is running: %s", url)
30             else:
31                 url = url_path_join(self.hub.server.base_url, 'home')
32                 self.log.debug("User is not running: %s", url)
33             self.redirect(url)
34             return
35         url = url_path_join(self.hub.server.base_url, 'login')
36         self.redirect(url)
37 
38 
39 class HomeHandler(BaseHandler):
40     """Render the user's home page."""
41 
42     @web.authenticated
43     def get(self):
44         html = self.render_template('home.html',
45             user=self.get_current_user(),
46         )
47         self.finish(html)
48 
49 
50 class SpawnHandler(BaseHandler):
51     """Handle spawning of single-user servers via form.
52     
53     GET renders the form, POST handles form submission.
54     
55     Only enabled when Spawner.options_form is defined.
56     """
57     @web.authenticated
58     def get(self):
59         """GET renders form for spawning with user-specified options"""
60         user = self.get_current_user()
61         if user.running:
62             url = user.server.base_url
63             self.log.debug("User is running: %s", url)
64             self.redirect(url)
65             return
66         if user.spawner.options_form:
67             html = self.render_template('spawn.html',
68                 user=self.get_current_user(),
69                 spawner_options_form=user.spawner.options_form,
70             )
71             self.finish(html)
72         else:
73             # not running, no form. Trigger spawn.
74             url = url_path_join(self.base_url, 'users', user.name)
75             self.redirect(url)
76     
77     @web.authenticated
78     @gen.coroutine
79     def post(self):
80         """POST spawns with user-specified options"""
81         user = self.get_current_user()
82         if user.running:
83             url = user.server.base_url
84             self.log.warning("User is already running: %s", url)
85             self.redirect(url)
86             return
87         form_options = {}
88         for key, byte_list in self.request.body_arguments.items():
89             form_options[key] = [ bs.decode('utf8') for bs in byte_list ]
90         options = user.spawner.options_from_form(form_options)
91         yield self.spawn_single_user(user, options=options)
92         self.set_login_cookie(user)
93         url = user.server.base_url
94         self.redirect(url)
95 
96 class AdminHandler(BaseHandler):
97     """Render the admin page."""
98 
99     @admin_only
100     def get(self):
101         available = {'name', 'admin', 'running', 'last_activity'}
102         default_sort = ['admin', 'name']
103         mapping = {
104             'running': '_server_id'
105         }
106         default_order = {
107             'name': 'asc',
108             'last_activity': 'desc',
109             'admin': 'desc',
110             'running': 'desc',
111         }
112         sorts = self.get_arguments('sort') or default_sort
113         orders = self.get_arguments('order')
114         
115         for bad in set(sorts).difference(available):
116             self.log.warn("ignoring invalid sort: %r", bad)
117             sorts.remove(bad)
118         for bad in set(orders).difference({'asc', 'desc'}):
119             self.log.warn("ignoring invalid order: %r", bad)
120             orders.remove(bad)
121         
122         # add default sort as secondary
123         for s in default_sort:
124             if s not in sorts:
125                 sorts.append(s)
126         if len(orders) < len(sorts):
127             for col in sorts[len(orders):]:
128                 orders.append(default_order[col])
129         else:
130             orders = orders[:len(sorts)]
131         
132         # this could be one incomprehensible nested list comprehension
133         # get User columns
134         cols = [ getattr(orm.User, mapping.get(c, c)) for c in sorts ]
135         # get User.col.desc() order objects
136         ordered = [ getattr(c, o)() for c, o in zip(cols, orders) ]
137         
138         users = self.db.query(orm.User).order_by(*ordered)
139         users = [ self._user_from_orm(u) for u in users ]
140         running = [ u for u in users if u.running ]
141         
142         html = self.render_template('admin.html',
143             user=self.get_current_user(),
144             admin_access=self.settings.get('admin_access', False),
145             users=users,
146             running=running,
147             sort={s:o for s,o in zip(sorts, orders)},
148         )
149         self.finish(html)
150 
151 
152 default_handlers = [
153     (r'/', RootHandler),
154     (r'/home', HomeHandler),
155     (r'/admin', AdminHandler),
156     (r'/spawn', SpawnHandler),
157 ]
158
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/jupyterhub/handlers/pages.py b/jupyterhub/handlers/pages.py
--- a/jupyterhub/handlers/pages.py
+++ b/jupyterhub/handlers/pages.py
@@ -71,7 +71,7 @@
             self.finish(html)
         else:
             # not running, no form. Trigger spawn.
-            url = url_path_join(self.base_url, 'users', user.name)
+            url = url_path_join(self.base_url, 'user', user.name)
             self.redirect(url)
     
     @web.authenticated

{"golden_diff": "diff --git a/jupyterhub/handlers/pages.py b/jupyterhub/handlers/pages.py\n--- a/jupyterhub/handlers/pages.py\n+++ b/jupyterhub/handlers/pages.py\n@@ -71,7 +71,7 @@\n             self.finish(html)\n         else:\n             # not running, no form. Trigger spawn.\n-            url = url_path_join(self.base_url, 'users', user.name)\n+            url = url_path_join(self.base_url, 'user', user.name)\n             self.redirect(url)\n     \n     @web.authenticated\n", "issue": "404 on single user notebook server anytime I restart jupyterhub\nI just deployed jupyterhub from scratch using my ansible scripts this morning. The script are unchanged from 2-3 weeks ago when I did it previously and it was all working. I am running from latest master of jupyterhub.\n\nAnytime I restart jupyterhub (hub+proxy) I see the following behavior:\n- I can log in (using GitHub OAuth)\n- Trying to start my server gives me a 404 on `/hub/users/ellisonbg`. I can tell from the server log that the single user server isn't being started.\n- I can go to the Admin page and start my server from there.\n- But then, I get a redirect loop when I try to go to my single user server.\n- If I clear all my cookies while my single user server (started through the Admin page) is still running, it starts to work as expected. I can start and stop the single user server on the control panel page just fine.\n- If a restart jupyterhub, the problems start all over again.\n\nI am using a fixed proxy_auth_token and cookie secret.\n\n", "before_files": [{"content": "\"\"\"Basic html-rendering handlers.\"\"\"\n\n# Copyright (c) Jupyter Development Team.\n# Distributed under the terms of the Modified BSD License.\n\nfrom tornado import web, gen\n\nfrom .. import orm\nfrom ..utils import admin_only, url_path_join\nfrom .base import BaseHandler\nfrom .login import LoginHandler\n\n\nclass RootHandler(BaseHandler):\n    \"\"\"Render the Hub root page.\n    \n    If logged in, redirects to:\n    \n    - single-user server if running\n    - hub home, otherwise\n    \n    Otherwise, renders login page.\n    \"\"\"\n    def get(self):\n        user = self.get_current_user()\n        if user:\n            if user.running:\n                url = user.server.base_url\n                self.log.debug(\"User is running: %s\", url)\n            else:\n                url = url_path_join(self.hub.server.base_url, 'home')\n                self.log.debug(\"User is not running: %s\", url)\n            self.redirect(url)\n            return\n        url = url_path_join(self.hub.server.base_url, 'login')\n        self.redirect(url)\n\n\nclass HomeHandler(BaseHandler):\n    \"\"\"Render the user's home page.\"\"\"\n\n    @web.authenticated\n    def get(self):\n        html = self.render_template('home.html',\n            user=self.get_current_user(),\n        )\n        self.finish(html)\n\n\nclass SpawnHandler(BaseHandler):\n    \"\"\"Handle spawning of single-user servers via form.\n    \n    GET renders the form, POST handles form submission.\n    \n    Only enabled when Spawner.options_form is defined.\n    \"\"\"\n    @web.authenticated\n    def get(self):\n        \"\"\"GET renders form for spawning with user-specified options\"\"\"\n        user = self.get_current_user()\n        if user.running:\n            url = user.server.base_url\n            self.log.debug(\"User is running: %s\", url)\n            self.redirect(url)\n            return\n        if user.spawner.options_form:\n            html = self.render_template('spawn.html',\n                user=self.get_current_user(),\n                spawner_options_form=user.spawner.options_form,\n            )\n            self.finish(html)\n        else:\n            # not running, no form. Trigger spawn.\n            url = url_path_join(self.base_url, 'users', user.name)\n            self.redirect(url)\n    \n    @web.authenticated\n    @gen.coroutine\n    def post(self):\n        \"\"\"POST spawns with user-specified options\"\"\"\n        user = self.get_current_user()\n        if user.running:\n            url = user.server.base_url\n            self.log.warning(\"User is already running: %s\", url)\n            self.redirect(url)\n            return\n        form_options = {}\n        for key, byte_list in self.request.body_arguments.items():\n            form_options[key] = [ bs.decode('utf8') for bs in byte_list ]\n        options = user.spawner.options_from_form(form_options)\n        yield self.spawn_single_user(user, options=options)\n        self.set_login_cookie(user)\n        url = user.server.base_url\n        self.redirect(url)\n\nclass AdminHandler(BaseHandler):\n    \"\"\"Render the admin page.\"\"\"\n\n    @admin_only\n    def get(self):\n        available = {'name', 'admin', 'running', 'last_activity'}\n        default_sort = ['admin', 'name']\n        mapping = {\n            'running': '_server_id'\n        }\n        default_order = {\n            'name': 'asc',\n            'last_activity': 'desc',\n            'admin': 'desc',\n            'running': 'desc',\n        }\n        sorts = self.get_arguments('sort') or default_sort\n        orders = self.get_arguments('order')\n        \n        for bad in set(sorts).difference(available):\n            self.log.warn(\"ignoring invalid sort: %r\", bad)\n            sorts.remove(bad)\n        for bad in set(orders).difference({'asc', 'desc'}):\n            self.log.warn(\"ignoring invalid order: %r\", bad)\n            orders.remove(bad)\n        \n        # add default sort as secondary\n        for s in default_sort:\n            if s not in sorts:\n                sorts.append(s)\n        if len(orders) < len(sorts):\n            for col in sorts[len(orders):]:\n                orders.append(default_order[col])\n        else:\n            orders = orders[:len(sorts)]\n        \n        # this could be one incomprehensible nested list comprehension\n        # get User columns\n        cols = [ getattr(orm.User, mapping.get(c, c)) for c in sorts ]\n        # get User.col.desc() order objects\n        ordered = [ getattr(c, o)() for c, o in zip(cols, orders) ]\n        \n        users = self.db.query(orm.User).order_by(*ordered)\n        users = [ self._user_from_orm(u) for u in users ]\n        running = [ u for u in users if u.running ]\n        \n        html = self.render_template('admin.html',\n            user=self.get_current_user(),\n            admin_access=self.settings.get('admin_access', False),\n            users=users,\n            running=running,\n            sort={s:o for s,o in zip(sorts, orders)},\n        )\n        self.finish(html)\n\n\ndefault_handlers = [\n    (r'/', RootHandler),\n    (r'/home', HomeHandler),\n    (r'/admin', AdminHandler),\n    (r'/spawn', SpawnHandler),\n]\n", "path": "jupyterhub/handlers/pages.py"}], "after_files": [{"content": "\"\"\"Basic html-rendering handlers.\"\"\"\n\n# Copyright (c) Jupyter Development Team.\n# Distributed under the terms of the Modified BSD License.\n\nfrom tornado import web, gen\n\nfrom .. import orm\nfrom ..utils import admin_only, url_path_join\nfrom .base import BaseHandler\nfrom .login import LoginHandler\n\n\nclass RootHandler(BaseHandler):\n    \"\"\"Render the Hub root page.\n    \n    If logged in, redirects to:\n    \n    - single-user server if running\n    - hub home, otherwise\n    \n    Otherwise, renders login page.\n    \"\"\"\n    def get(self):\n        user = self.get_current_user()\n        if user:\n            if user.running:\n                url = user.server.base_url\n                self.log.debug(\"User is running: %s\", url)\n            else:\n                url = url_path_join(self.hub.server.base_url, 'home')\n                self.log.debug(\"User is not running: %s\", url)\n            self.redirect(url)\n            return\n        url = url_path_join(self.hub.server.base_url, 'login')\n        self.redirect(url)\n\n\nclass HomeHandler(BaseHandler):\n    \"\"\"Render the user's home page.\"\"\"\n\n    @web.authenticated\n    def get(self):\n        html = self.render_template('home.html',\n            user=self.get_current_user(),\n        )\n        self.finish(html)\n\n\nclass SpawnHandler(BaseHandler):\n    \"\"\"Handle spawning of single-user servers via form.\n    \n    GET renders the form, POST handles form submission.\n    \n    Only enabled when Spawner.options_form is defined.\n    \"\"\"\n    @web.authenticated\n    def get(self):\n        \"\"\"GET renders form for spawning with user-specified options\"\"\"\n        user = self.get_current_user()\n        if user.running:\n            url = user.server.base_url\n            self.log.debug(\"User is running: %s\", url)\n            self.redirect(url)\n            return\n        if user.spawner.options_form:\n            html = self.render_template('spawn.html',\n                user=self.get_current_user(),\n                spawner_options_form=user.spawner.options_form,\n            )\n            self.finish(html)\n        else:\n            # not running, no form. Trigger spawn.\n            url = url_path_join(self.base_url, 'user', user.name)\n            self.redirect(url)\n    \n    @web.authenticated\n    @gen.coroutine\n    def post(self):\n        \"\"\"POST spawns with user-specified options\"\"\"\n        user = self.get_current_user()\n        if user.running:\n            url = user.server.base_url\n            self.log.warning(\"User is already running: %s\", url)\n            self.redirect(url)\n            return\n        form_options = {}\n        for key, byte_list in self.request.body_arguments.items():\n            form_options[key] = [ bs.decode('utf8') for bs in byte_list ]\n        options = user.spawner.options_from_form(form_options)\n        yield self.spawn_single_user(user, options=options)\n        self.set_login_cookie(user)\n        url = user.server.base_url\n        self.redirect(url)\n\nclass AdminHandler(BaseHandler):\n    \"\"\"Render the admin page.\"\"\"\n\n    @admin_only\n    def get(self):\n        available = {'name', 'admin', 'running', 'last_activity'}\n        default_sort = ['admin', 'name']\n        mapping = {\n            'running': '_server_id'\n        }\n        default_order = {\n            'name': 'asc',\n            'last_activity': 'desc',\n            'admin': 'desc',\n            'running': 'desc',\n        }\n        sorts = self.get_arguments('sort') or default_sort\n        orders = self.get_arguments('order')\n        \n        for bad in set(sorts).difference(available):\n            self.log.warn(\"ignoring invalid sort: %r\", bad)\n            sorts.remove(bad)\n        for bad in set(orders).difference({'asc', 'desc'}):\n            self.log.warn(\"ignoring invalid order: %r\", bad)\n            orders.remove(bad)\n        \n        # add default sort as secondary\n        for s in default_sort:\n            if s not in sorts:\n                sorts.append(s)\n        if len(orders) < len(sorts):\n            for col in sorts[len(orders):]:\n                orders.append(default_order[col])\n        else:\n            orders = orders[:len(sorts)]\n        \n        # this could be one incomprehensible nested list comprehension\n        # get User columns\n        cols = [ getattr(orm.User, mapping.get(c, c)) for c in sorts ]\n        # get User.col.desc() order objects\n        ordered = [ getattr(c, o)() for c, o in zip(cols, orders) ]\n        \n        users = self.db.query(orm.User).order_by(*ordered)\n        users = [ self._user_from_orm(u) for u in users ]\n        running = [ u for u in users if u.running ]\n        \n        html = self.render_template('admin.html',\n            user=self.get_current_user(),\n            admin_access=self.settings.get('admin_access', False),\n            users=users,\n            running=running,\n            sort={s:o for s,o in zip(sorts, orders)},\n        )\n        self.finish(html)\n\n\ndefault_handlers = [\n    (r'/', RootHandler),\n    (r'/home', HomeHandler),\n    (r'/admin', AdminHandler),\n    (r'/spawn', SpawnHandler),\n]\n", "path": "jupyterhub/handlers/pages.py"}]}