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This question already has an answer here:

I sometimes experience whole Ubuntu freezes (from 14.04 to 16.04, I upgrade by a clean installation), just mouse can move (that's why this question is different from others). I think this is caused by one of the cores stop working when 100% load by unresponsive Desktop Environment. There isn't any magic key combination like Ctrl+Alt+Del or Ctrl+Shift+Esc known from Windows. The only thing I could do is hold power button for 5-10 seconds and hard shut down. Is there any other recommended solution?

Could I e.g. with some keyword combination reset CPU or kill all additional services or reset Unity or force soft reboot or I don't know what else could help?

marked as duplicate by Videonauth, MadMike, Elder Geek, Mark Kirby, Ron Jun 7 '16 at 18:09

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    Can you access another tty? Ctrl + Alt + F1 (changing F1 to F1-F6 to access the terminal that you want) – user508889 Jun 6 '16 at 13:20
  • @bc2946088 I'll try next time – aleskva Jun 6 '16 at 13:23
  • @Parto I ask about killing unresponsive OS (or Desktop Environment), not application – aleskva Jun 6 '16 at 13:25
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    I don't think it's a duplicate, atleast of that link @Parto. They're talking about individual applications within Unity they want to stop. Not when Unity itself goes unresponsive. – user508889 Jun 6 '16 at 13:25
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    The reason this is a duplicate is because the mouse moving is a red herring. It just means you have hardware cursor support, which means mouse movement bypasses the OS entirely. – rich remer Jun 7 '16 at 4:34
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Switch to the console: CTRL + ALT + F1

After login, you can see which processes are running using this command:

ps -ef

If you see a process which has high CPU usage, you can kill it.

sudo kill <pid>

Of course, you can simply restart the PC too:

sudo reboot
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    In case ctrl+alt+f1 does not work, it is worth trying with an ssh client instead. – kasperd Jun 6 '16 at 19:32
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    As an alternative to ps -ef you could also try "top" and/or "sudo iotop". – aap Jun 6 '16 at 22:37
  • For some reason, only Ctrl+Alt+F3 works and F1 to bring up the console. – FreeKrishna Jun 2 '18 at 16:39
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Well there is a magic key combination (to reboot):

While holding Alt and the SysReq (Print Screen) keys, type REISUB

For more details visit this answer : https://askubuntu.com/a/36717/497359

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    ConflictBoy solution is preferrable if it works. Also I believe it's possible to disable kernel's "magic keys", in which case this wont work. – Bakuriu Jun 6 '16 at 17:05
  • @Bakuriu Yes, I just posted this answer as the Op was asking "magic key combination" similar to ctrl+alt+del in his question, ConflitBoy solution is preferable indeed. – Severus Tux Jun 6 '16 at 17:09
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    @Bakuriu: Ubuntu disables many of the magic sysrq key combos by default (like Memory, Processes, and other info dumps). At least Umount, Sync, and reBoot are left enabled in a default install, though. (I use them in that order when things are totally locked and I can't get in with ssh or a text console. remount-ro implies any necessary syncing, and then sync after the filesystems are already read-only makes sure that nothing can be dirtied between then and reBoot.) If you've had bad USB hardware, then it's easy to form a mental association between computer crapping out and typing USB :P – Peter Cordes Jun 8 '16 at 7:53
  • I have got those separate, so SysReq or Print Screen? And I can use them only with fn key pressed, will this work too? – aleskva Jun 22 '16 at 2:07
  • okay, I googled out it is SysReq and it will work with fn too – aleskva Jun 22 '16 at 2:08

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