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I was stupid, I kept ignoring the warnings that my harddrive space was running low and left a download running in the background. When I logged out, I wasn't taken back to the login screen (LightDM), and when I rebooted I didn't get the login screen either. Instead I got a terminal-like screen that listed drivers/daemons being loaded, but didn't have a prompt. I could still access the terminal with Ctrl-Alt-F1 (and F2 etc).

After barking up many wrong trees I solved it by deleting a file or two. My question is, why did this happen?

lofidevops
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2 Answers2

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If the root partition has filled (or the partition that holds /var to be more precise), there will not be any space to write to /var/log/auth.log, which usually prevents login attempts from anyone besides the superuser.

The same goes for /home. There are files in your home directory that have to be updated and if there is no space left on the device will prevent you from logging in.

Rinzwind
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    It's worth noting that even though its easily explained, we still consider this to be a pretty serious bug. You shouldn't have to drop down to a VT to log in when your disk is full. – tumbleweed Mar 26 '12 at 10:28
  • afaik it is not needed to drop down to a VT. failsafe mode should still work (though I do not have a hdd to test this on ;)) @tumbleweed – Rinzwind Mar 26 '12 at 10:39
  • @tumbleweed is there a launchpad bug I can subscribe to? – lofidevops Mar 27 '12 at 13:32
  • @tumbleweed or rinzwind - by the way, do you happen to know the name of the terminal-like screen I described? – lofidevops Mar 27 '12 at 13:34
  • That's probably the normal boot screen where the commands are shown during booting (Ubuntu nowadays hides this but it is still there). – Rinzwind Mar 27 '12 at 15:07
  • @d3vid: It's just called a Virtual Terminal (VT). I'm guessing it's bug #35217, which is a fairly ancient bug. Oh, and hi to another Capetonian :) – tumbleweed Mar 27 '12 at 15:34
  • @Rinzwind: Failsafe doesn't work. I tried it. – Joshua Nov 22 '16 at 19:08
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Either /tmp filled up so it couldn't create .X11-unix or /home filled up so it couldn't create .Xauthority. Either way, graphical login would be nonfunctional.

Modern Ubuntu defaults to a RAM-backed /tmp; however I recall in 2012 this was not the case.

Joshua
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  • This does not really answer the question. If you have a different question, you can ask it by clicking Ask Question. You can also add a bounty to draw more attention to this question. - From Review – Elder Geek Nov 22 '16 at 17:03
  • The heck it doesn't answer the question. Fill up /tmp and watch the behavior I just described happen. By default /tmp is on / in ubuntu and he probably did a single partition install. On the other hand the answer about logging is dead wrong. If true, logging into a TTY wouldn't work either. – Joshua Nov 22 '16 at 19:07
  • .Xauthority lives in ~ (/home/username) your answer is only accurate if /tmp is on the same partition as that. That assumes facts not in evidence. @Rinzwind answer is more precise. Yours could be. I recommend you [edit] to provide the detail that makes your answer true. – Elder Geek Nov 22 '16 at 19:24
  • See: http://askubuntu.com/questions/173094/how-can-i-use-ram-storage-for-the-tmp-directory-and-how-to-set-a-maximum-amount – Elder Geek Nov 22 '16 at 19:43