It already happened to me 2 times before but I wasn't on the newest version then (6.8.1). I upgraded to 6.8.3 thinking the problem would be solved with this upgrade but it happened again. A restart solves this problem and gets the webUI up and running again.
When trying to access the webUI I get 500 Internal Server Error. Everything else is working (VMs, Docker container, plugins etc.)
This comes up in the nginx error log when I want to access the webUI.
2020/03/28 16:18:29 [error] 27546#27546: *3245721 FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream, client: 192.168.0.113, server: , request: "GET /Dashboard HTTP/1.1", subrequest: "/auth_request.php", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "192.168.0.156"
2020/03/28 16:18:29 [error] 27546#27546: *3245721 auth request unexpected status: 404 while sending to client, client: 192.168.0.113, server: , request: "GET /Dashboard HTTP/1.1", host: "192.168.0.156"
Sadly, I cannot get the diagnostics from the CLI.
root@Tower:~# diagnostics
Warning: Unknown: failed to open stream: No such file or directory in Unknown on line 0
Fatal error: Unknown: Failed opening required '/usr/local/emhttp/webGui/include/local_prepend.php' (include_path='.:/usr/local/emhttp') in Unknown on line 0
The folder /usr/local/emhttp/ is completely empty except for plugins, so can't run the diagnostics tool/don't know how else to run it.
I suppose a work around for this is just copying the webGui folder onto the array or somewhere and when the folder disappears again, copying the folder back to /usr/local/emhttp/ will make it work. However, I'd really like to know what is causing the whole folder to disappear. The webGui folder was there 14 hours ago, then I went to bed, so I didn't do anything to the server since then.
Edit: Since the post it happened again a few times. A workaround is creating a backup of the emhttp folder and then inserting it when the webUI is missing again. The diagnostics are from after restoring the webUI by copying the stuff
syslog
tower-diagnostics-20200428-1751.zip