This is a 20.04 Ubuntu PC running a Shinobi server and not much else.
Shinobi has a default behaviour that when a new camera is added it will constantly save its video files into the Shinobi admin user's home folder at /home/Shinobi/videos
And it will keep doing this until the whole hard disk is full.
When it has done this, it has (it seems) prevented Ubuntu from booting normally and opening Gnome. The Plymouth loading screen appears and it then displays a black screen with a flashing white cursor.
To fix this I was able to:-
Ctrl+Alt+F2 to open a terminal session
sudo nano /etc/default/grub
Looked for the line 'GRUB_CMDLINE_LINUX_DEFAULT=""' and added "nomodeset" and removed "quiet" so that on the next boot I was able to see error messages.
update-grub
The error messages didn't mention out of space but said some firmware needed updating. When I tried sudo apt-get update it then gave an error that there was no space available on the device.
So next I used
du -hs * | sort -hr
to find that a camera had made itself a subfolder in the /home/Shinobi/videos folder. I navigated into that subfolder and did sudo rm . to delete the video files.
Gnome now loads as normal again, but since this is a (to me undesirable) default behaviour in Shinobi whenever a new camera is added, is there some way I can make Ubuntu reserve enough space for itself to boot? Or is there a logfile I can check to find out what Gnome would have needed to write in order for it to start up?