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I am experiencing occasional system freezes with Ubuntu 16.04 using the Gnome 3 Desktop. The logging output in /var/log is not really helpful. There are no files in /var/crash. I have not been able to identify a pattern in the last log entries before the freeze. I would like to investigate the problem further or file a bug report, but I ran out of ideas how to track it down. Here are the symptoms (similar to those Mysterious minutes-long system freeze):

  • The UI freezes except the mouse cursor, which still responds with a latency of several seconds (it jumps roughly in the direction of the mouse movement).
  • The system usually does not respond to keyboard input. Sometimes I was able to ctrl-alt-f1 to the console, but I was rarely able to login. I never succeeded to execute a command (e.g. dmesg, sudo init 6). Even sysrq-o would not work.
  • The HDD LED is illuminated constantly.
  • Judging by the fan speed, the CPU runs under high load.

The only recovery is a hard reset/reboot. I am suspecting that the freezes occured in the following situations:

  • High memory usage
  • A VirtualBox VM (windows guest) is running or has been running for a while (e.g. several days)

However, the logfiles give no hints in that direction. There are for example no messages of the OOM killer. How should I proceed to identfy the exact error conditions?

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Creating a large swap partition made the problem vanish. It seems that under certain conditions the system was running out of memory so quickly that even the OOM killer did not have a chance to run (or its output being logged to a persistent location). However, I did not identify the root cause of the spiking memory usage.

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