"You don't have permission to access / on this server."

What is the problem?

When accessing Octoprint the browser displays "Forbidden
You don't have permission to access / on this server."

What did you already try to solve it?

Restarted the Raspberry Pi.
Shutdown OctoPrint then restarted in safe mode.

Have you tried running in safe mode and if so did it solve the issue?

Yes. It did not.

Complete Logs

pi@octopi : ~/.octoprint/logs $ ~/oprint/bin/octoprint serve --safe

2020-11-30 22:54:55,629 - octoprint.startup - INFO - ******************************************************************************

2020-11-30 22:54:55,632 - octoprint.startup - INFO - Starting OctoPrint 1.5.0

2020-11-30 22:54:55,633 - octoprint.startup - INFO - Starting in SAFE MODE. Third party plugins will be disabled!

2020-11-30 22:54:55,633 - octoprint.startup - INFO - Reason for safe mode: command line flag

2020-11-30 22:54:55,635 - octoprint.startup - INFO - ******************************************************************************

2020-11-30 22:54:55,776 - octoprint.util.connectivity.connectivity_checker - INFO - Connectivity changed from offline to online

2020-11-30 22:54:55,813 - octoprint.util.connectivity.connectivity_checker - INFO - Connectivity state is currently: online

2020-11-30 22:54:55,813 - octoprint.util.connectivity.connectivity_checker - INFO - Connecting to 8.8.8.8:53 is working

2020-11-30 22:54:55,814 - octoprint.util.connectivity.connectivity_checker - INFO - Resolving octoprint.org is working

2020-11-30 22:54:56,572 - octoprint.startup - INFO - Blacklist processing done, adding 10 blacklisted plugin versions: roomtemp (any), GcodeEditor (0.1.1), GcodeEditor (0.2.0), GcodeEditor (0.2.1), GcodeEditor (0.2.2), GcodeEditor (0.2.3), GcodeEditor (0.2.4), GcodeEditor (0.2.5), GcodeEditor (0.2.6), GcodeEditor (0.2.8)

2020-11-30 22:54:56,617 - octoprint.plugin.core - INFO - Loading plugins from /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins, /home/pi/.octoprint/plugins and installed plugin packages...

2020-11-30 22:54:58,748 - octoprint.plugin.core - WARNING - Plugin Room Temperature Plugin (1.0) is blacklisted.

2020-11-30 22:54:59,380 - octoprint.plugin.core - INFO - Found 28 plugin(s) providing 17 mixin implementations, 34 hook handlers

2020-11-30 22:54:59,513 - octoprint.server.heartbeat - INFO - Starting server heartbeat, 900.0s interval

2020-11-30 22:54:59,548 - octoprint.server - INFO - Intermediary server started

2020-11-30 22:54:59,599 - octoprint.filemanager.storage - INFO - Initializing the file metadata for /home/pi/.octoprint/uploads...

2020-11-30 22:55:00,229 - octoprint.filemanager.storage - INFO - ... file metadata for /home/pi/.octoprint/uploads initialized successfully.

2020-11-30 22:55:00,236 - octoprint.server - INFO - Added new permission from plugin action_command_notification: PLUGIN_ACTION_COMMAND_NOTIFICATION_SHOW (needs: u"Need(method='role', value=u'plugin_action_command_notification_show')")

2020-11-30 22:55:00,238 - octoprint.server - INFO - Added new permission from plugin action_command_notification: PLUGIN_ACTION_COMMAND_NOTIFICATION_CLEAR (needs: u"Need(method='role', value=u'plugin_action_command_notification_clear')")

2020-11-30 22:55:00,241 - octoprint.server - INFO - Added new permission from plugin action_command_prompt: PLUGIN_ACTION_COMMAND_PROMPT_INTERACT (needs: u"Need(method='role', value=u'plugin_action_command_prompt_interact')")

2020-11-30 22:55:00,244 - octoprint.server - INFO - Added new permission from plugin announcements: PLUGIN_ANNOUNCEMENTS_READ (needs: u"Need(method='role', value=u'plugin_announcements_read')")

2020-11-30 22:55:00,247 - octoprint.server - INFO - Added new permission from plugin announcements: PLUGIN_ANNOUNCEMENTS_MANAGE (needs: u"Need(method='role', value=u'plugin_announcements_manage'), Need(method='role', value=u'plugin_announcements_read')")

2020-11-30 22:55:00,250 - octoprint.server - INFO - Added new permission from plugin appkeys: PLUGIN_APPKEYS_ADMIN (needs: u"Need(method='role', value=u'plugin_appkeys_admin')")

2020-11-30 22:55:00,253 - octoprint.server - INFO - Added new permission from plugin backup: PLUGIN_BACKUP_ACCESS (needs: u"Need(method='role', value=u'plugin_backup_access')")

2020-11-30 22:55:00,256 - octoprint.server - INFO - Added new permission from plugin firmware_check: PLUGIN_FIRMWARE_CHECK_DISPLAY (needs: u"Need(method='role', value=u'plugin_firmware_check_display')")

2020-11-30 22:55:00,260 - octoprint.server - INFO - Added new permission from plugin logging: PLUGIN_LOGGING_MANAGE (needs: u"Need(method='role', value=u'plugin_logging_manage')")

2020-11-30 22:55:00,262 - octoprint.server - INFO - Added new permission from plugin pi_support: PLUGIN_PI_SUPPORT_STATUS (needs: u"Need(method='role', value=u'plugin_pi_support_check')")

2020-11-30 22:55:00,265 - octoprint.server - INFO - Added new permission from plugin pluginmanager: PLUGIN_PLUGINMANAGER_MANAGE (needs: u"Need(method='role', value=u'plugin_pluginmanager_manage')")

2020-11-30 22:55:00,267 - octoprint.server - INFO - Added new permission from plugin pluginmanager: PLUGIN_PLUGINMANAGER_INSTALL (needs: u"Need(method='role', value=u'plugin_pluginmanager_install'), Need(method='role', value=u'plugin_pluginmanager_manage')")

2020-11-30 22:55:00,270 - octoprint.server - INFO - Added new permission from plugin softwareupdate: PLUGIN_SOFTWAREUPDATE_CHECK (needs: u"Need(method='role', value=u'plugin_softwareupdate_check')")

2020-11-30 22:55:00,272 - octoprint.server - INFO - Added new permission from plugin softwareupdate: PLUGIN_SOFTWAREUPDATE_UPDATE (needs: u"Need(method='role', value=u'plugin_softwareupdate_update')")

2020-11-30 22:55:00,274 - octoprint.server - INFO - Added new permission from plugin softwareupdate: PLUGIN_SOFTWAREUPDATE_CONFIGURE (needs: u"Need(method='role', value=u'plugin_softwareupdate_configure')")

2020-11-30 22:55:00,897 - octoprint.plugins.softwareupdate - INFO - Loaded version cache from disk

2020-11-30 22:55:03,042 - octoprint.util.pip - INFO - Using "/home/pi/oprint/bin/python2 -m pip" as command to invoke pip

2020-11-30 22:55:05,104 - octoprint.util.pip - INFO - Version of pip is 9.0.3

2020-11-30 22:55:05,106 - octoprint.util.pip - INFO - pip installs to /home/pi/oprint/lib/python2.7/site-packages (writable -> yes), --user flag needed -> no, virtual env -> yes

2020-11-30 22:55:05,108 - octoprint.util.pip - INFO - ==> pip ok -> yes

2020-11-30 22:55:05,138 - octoprint.plugin.core - INFO - Initialized 17 plugin implementation(s)

2020-11-30 22:55:05,168 - octoprint.plugin.core - INFO - 28 plugin(s) registered with the system:

| Action Command Notification Support (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/action_command_notification

| Action Command Prompt Support (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/action_command_prompt

| Announcement Plugin (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/announcements

| Anonymous Usage Tracking (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/tracking

| Application Keys Plugin (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/appkeys

| Backup & Restore (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/backup

| Core Wizard (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/corewizard

| !Dashboard (1.16.3) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_dashboard

| Discovery (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/discovery

| !DisplayLayerProgress Plugin (1.24.0) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_DisplayLayerProgress

| !Enclosure Plugin (4.12) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_enclosure

| Error Tracking (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/errortracking

| File Check (2020.8.7) (bundled) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_file_check

| Firmware Check (2020.9.23) (bundled) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_firmware_check

| GCode Viewer (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/gcodeviewer

| !GcodeEditor (0.2.9) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_GcodeEditor

| Logging (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/logging

| !M117NavBar (0.1.1) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_M117NavBar

| Pi Support Plugin (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/pi_support

| Plugin Manager (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/pluginmanager

| !Preheat Button (0.5.1) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_preheat

| !Pushover (0.3.8) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_pushover

| #Room Temperature Plugin (1.0) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_roomtemp

| !Simple Emergency Stop (1.0.4) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_simpleemergencystop

| Software Update (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/softwareupdate

| !Tab Order (0.5.12) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_taborder

| !Terminal Commands (0.1.6) = /home/pi/oprint/local/lib/python2.7/site-packages/octoprint_TerminalCommands

| Virtual Printer (bundled) = /home/pi/oprint/lib/python2.7/site-packages/octoprint/plugins/virtual_printer

Prefix legend: ! = disabled, # = blacklisted, * = incompatible

2020-11-30 22:55:05,218 - octoprint.environment - INFO - Detected environment is Python 2.7.13 under Linux (linux2). Details:

| hardware:

| cores: 4

| freq: 1400.0

| ram: 917016576

| os:

| bits: 32

| id: linux

| platform: linux2

| plugins:

| pi_support:

| model: Raspberry Pi 3 Model B Plus Rev 1.3

| octopi_version: 0.15.1

| throttle_state: '0x0'

| python:

| pip: 9.0.3

| version: 2.7.13

| virtualenv: /home/pi/oprint

2020-11-30 22:55:05,235 - octoprint.server - INFO - Reset webasset folder /home/pi/.octoprint/generated/webassets...

2020-11-30 22:55:05,237 - octoprint.server - INFO - Reset webasset folder /home/pi/.octoprint/generated/.webassets-cache...

2020-11-30 22:55:06,838 - octoprint.server - INFO - Shutting down intermediary server...

2020-11-30 22:55:07,288 - octoprint.server - INFO - Intermediary server shut down

2020-11-30 22:55:07,293 - octoprint.events - INFO - Processing startup event, this is our first event

2020-11-30 22:55:07,298 - octoprint.events - INFO - Adding 2 events to queue that were held back before startup event

2020-11-30 22:55:07,301 - octoprint.filemanager - INFO - Adding backlog items from all storage types to analysis queue...

2020-11-30 22:55:07,310 - octoprint.server.util.watchdog - INFO - Running initial scan on watched folder...

2020-11-30 22:55:07,329 - octoprint.server.util.watchdog - INFO - ... initial scan done.

2020-11-30 22:55:07,388 - octoprint.plugins.softwareupdate - INFO - Fetching check overlays from https://plugins.octoprint.org/update_check_overlay.json

2020-11-30 22:55:07,386 - octoprint.plugins.pluginmanager - INFO - Loaded plugin repository data from disk, was still valid

2020-11-30 22:55:07,390 - octoprint.filemanager - INFO - Added 0 items from storage type "local" to analysis queue

2020-11-30 22:55:08,340 - octoprint.plugins.discovery - INFO - Registered 'OctoPrint instance on octopi._http._tcp.local.' for _http._tcp.local.

2020-11-30 22:55:08,525 - octoprint.plugins.tracking - INFO - Sent tracking event system_unthrottled, payload: {u'throttled_mask': 0, u'throttled_voltage_now': False, u'throttled_voltage_past': False, u'throttled_overheat_now': False, u'throttled_now': False, u'throttled_past': False, u'throttled_overheat_past': False}

2020-11-30 22:55:09,374 - octoprint.plugins.discovery - INFO - Registered 'OctoPrint instance on octopi._octoprint._tcp.local.' for _octoprint._tcp.local.

2020-11-30 22:55:09,672 - octoprint.plugins.discovery - INFO - Registered OctoPrint instance on octopi for SSDP

2020-11-30 22:55:09,908 - octoprint.server - INFO - Listening on http://0.0.0.0:5000 and http://[::]:5000

2020-11-30 22:55:10,065 - octoprint.plugins.pluginmanager - INFO - Loaded notice data from disk, was still valid

2020-11-30 22:55:10,174 - octoprint.plugins.pluginmanager - INFO - Loaded plugin repository data from disk, was still valid

2020-11-30 22:55:12,606 - octoprint.util.pip - INFO - Using "/home/pi/oprint/bin/python2 -m pip" as command to invoke pip

2020-11-30 22:55:12,619 - octoprint.util.pip - INFO - pip installs to /home/pi/oprint/lib/python2.7/site-packages (writable -> yes), --user flag needed -> no, virtual env -> yes

2020-11-30 22:55:12,625 - octoprint.util.pip - INFO - ==> pip ok -> yes

2020-11-30 22:55:13,170 - octoprint.plugins.pluginmanager - INFO - Loaded notice data from disk, was still valid

2020-11-30 22:55:13,174 - octoprint.plugins.softwareupdate - INFO - Minimum free storage across all update relevant locations is 5.2GB. That is considered sufficient for updating.

2020-11-30 22:55:14,064 - octoprint.plugins.tracking - INFO - Sent tracking event startup, payload: {u'python': '2.7.13', u'os': u'linux', u'ram': 917016576, u'octopi_version': u'0.15.1', u'version': u'1.5.0', u'pip': '9.0.3', u'cores': 4, u'freq': 1400.0, u'pi_model': u'Raspberry Pi 3 Model B Plus Rev 1.3', u'bits': 32}

2020-11-30 22:55:14,118 - octoprint.server.preemptive_cache - INFO - Preemptively caching / (ui _default) for {'query_string': 'l10n=en', 'path': '/', 'base_url': 'http://octopi.local/'}

2020-11-30 22:55:14,819 - octoprint.plugins.tracking - INFO - Sent tracking event pong, payload: {u'python': '2.7.13', u'os': u'linux', u'ram': 917016576, u'octopi_version': u'0.15.1', u'version': u'1.5.0', u'plugins': u'', u'pip': '9.0.3', u'cores': 4, u'freq': 1400.0, u'pi_model': u'Raspberry Pi 3 Model B Plus Rev 1.3', u'bits': 32}

2020-11-30 22:55:15,741 - octoprint.plugins.tracking - INFO - Sent tracking event ping, payload: {'octoprint_uptime': 15}

2020-11-30 22:55:30,433 - octoprint.server.preemptive_cache - INFO - ... done in 16.32s

Additional information about your setup

OctoPi: ?
OctoPrint: 1.5.0 - issue occurred immediately following in-app update from 1.4.2(?) to 1.5.0.

Did you have access control enabled previously?

Check if you have a users.yaml file, if you do, try deleting it and restarting the server.

Edit: btw, that file will be under ~/.octoprint/

I also see you are running OctoPi 0.15, which is no longer supported and I suggest you upgrade.