All operating systems freeze sometimes, and Ubuntu is no exception. What should I do to regain control when...

  • just one program stops responding?
  • nothing at all responds to mouse clicks or key presses?
  • the mouse stops moving entirely?
  • I have an Intel Bay Trail CPU?

In what order should I try various solutions before deciding to pull the power plug?

What should I do when starting up Ubuntu fails? Is there a diagnostic procedure I can follow?


47 Answers 47


If it locks up completely, you can REISUB it, which is a safer alternative to just cold rebooting the computer.


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

R:  Switch to XLATE mode
E:  Send Terminate signal to all processes except for init
I:  Send Kill signal to all processes except for init
S:  Sync all mounted file-systems
U:  Remount file-systems as read-only
B:  Reboot

Some mnemonics for REISUB:

  • Rise up (from the dead) if you're inclined to zombie movies
  • BUSIER backwards, as in The System is busier than it should be!
  • Reboot Even If System Utterly Broken.
  • Or the classic: Raising Elephants Is So Utterly Boring

This is the SysReq key:

SysReq key

NOTE: There exists a less radical way than rebooting the whole system. If SysReq key works, you can kill processes one-by-one using Alt+SysReq+F. Kernel will kill the mostly «expensive» process each time. If you want to kill all processes for one console, you can issue Alt+SysReq+K.

NOTE: You should explicitly enable these key combinations. Ubuntu ships with sysrq default setting 176 (128+32+16), which allows to run only SUB part of REISUB combination. You can change it to 1 (all commands enabled) or 244 which is potentially less harmful. To do this:

sudo nano /etc/sysctl.d/10-magic-sysrq.conf

and switch 176 to 244; then

echo 244 | sudo tee /proc/sys/kernel/sysrq

It will immediately work! You can test this by pressing Alt+SysReq+F. For me, it killed the active browser tab, then all extensions. And if you will continue, you can reach X Server restart.

More info on all the Alt+SysReq functions here.

  • 138
    In the event you're forced to do this, do it slowly. Let a few seconds pass in between each keypress so that the commands you're invoking have a chance to finish before you go to the next one. Commented Apr 24, 2011 at 8:22
  • 28
    In case you like mnemonics: Raising Elephants Is So Utterly Boring, or Reboot Event If System Utterly Broken. I've also seen it as RSEIUB (Raising Skinny Elephants is Utterly Boring). Commented Apr 26, 2011 at 14:19
  • 16
    I actually came up with this one and try to remember it this way: "Reset System Environment In UBuntu". or "Reset Environment In System UBuntu". Commented Aug 14, 2012 at 21:32
  • 4
    What do you do if you're using a Mac that has no SysRq key?
    – Cerin
    Commented Jan 9, 2013 at 23:22
  • 7
    @Cerin How do I use REISUB with an Apple slim aluminum keyboard?
    – ændrük
    Commented Jan 12, 2013 at 19:56

When a single program stops working:

When a program window stops responding, you can usually stop it by clicking the X-shaped close button at the top left of the window. That will generally result in a dialog box saying that the program is not responding (but you already knew that) and presenting you with the option to kill the program or to continue to wait for it to respond.

Sometimes this does not work as expected. If you can't close a window by normal means, you can hit Alt+F2, type xkill, and press Enter. Your mouse cursor will then turn into an X. Hover over the offending window and left-click to kill it. Right clicking will cancel and return your mouse to normal.

If your program is running from a terminal, on the other hand, you can usually halt it with Ctrl+C. If not, find the name and process ID of its command, and tell the program to end as soon as possible with kill [process ID here]. It sends the default signal SIGTERM (15). If all else fails, as a last resort send SIGKILL (9): kill -9 [process ID here]. Note that you should only use SIGKILL as a last resort, because the process will be terminated immediately by the kernel with no opportunity for cleanup. It does not even get the signal - it just stops to exist.

(Killing a process by kill -9 allways works if you have the permission to kill. In some special cases the process is still listed by ps or top (as "zombie") - in this case, the program was killed, but the process table entry is kept, becuse it's needed later.)

When the mouse stops working:

If the keyboard still works, press Alt+F2 and run gnome-terminal (or, if these fail to launch, press Alt+Ctrl+F1 and login with your username and password). From there you can troubleshoot things. I'm not going to get into mouse troubleshooting here, as I haven't researched it. If you just want to try restarting the GUI, run sudo service lightdm restart. This should bring down the GUI, which will then attempt to respawn, bringing you back to the login screen.

When you have an Intel Bay Trail CPU

See https://askubuntu.com/a/803649/225694.

When everything, keys and mouse and all, stop working:

First try the Magic SysReq method outlined in Phoenix' answer. If that doesn't work, press the Reset button on the computer case. If even that doesn't work, you'll just have to power-cycle the machine.
May you never reach this point.

  • 10
    I've recently discovered that, rather than the "ps $options | grep $process_name" referenced above, one can just enter "pgrep $process_name" to achieve approximately the same result (for certain values of $options).
    – koanhead
    Commented Jun 4, 2011 at 13:45
  • 7
    One should never recommend kill -9 right off the bat. Once should instead attempt to kill the process with less drastic signals first, and only use -9 if all else fails. Commented Sep 28, 2012 at 4:18
  • 2
    sudo service lightdm restart: Not awesome - will kill all gui processes in Ubuntu 13.04 at least - for me that included running Virtual Machines etc :(
    – Stephen
    Commented Jul 9, 2013 at 23:04
  • 6
    "May you never reach this point." In most Linuxes, this is the only point reached. I have never seen a Linux freeze that can be fixed. Commented Jul 14, 2017 at 10:23
  • 2
    I must say this Alt+F2, type xkill was a crazy thing i didn't knew, totally saved the day Commented May 28, 2019 at 21:25

You can make the shortcut Ctrl+Alt+Delete open the System Monitor, with which you can kill any unresponsive applications.

  1. Open up System ➜ Preferences ➜ Keyboard Shortcuts and click Add.
    In the Command field, enter gnome-system-monitor. Name the shortcut whatever you want.

enter image description here

  1. Click Apply and then click where it says Disabled. Now hit the keys Ctrl+Alt+Delete

enter image description here

  1. Close Keyboard Shortcuts and try out the shortcut:

enter image description here

  • 9
    but if X is locking up fully, or even the kernel is hung, you can't do much with a keyboard shortcut.
    – nanofarad
    Commented Jun 14, 2012 at 21:58
  • 29
    Unfortunately, System Monitor is quite CPU intensive. It typically consumes up to 20% of my CPU, so if you're computer's bogged down, launching SM is only going to grind it into the dirt faster.
    – Cerin
    Commented Jan 9, 2013 at 23:25
  • 4
    If you can open System Monitor you can get to a terminal, in which case your OS is not frozen.
    – nbm
    Commented Nov 11, 2013 at 23:32
  • 2
    System Monitor is, unfortunately, not the trusty Task Manager on Windows. As commented above, it will only launch if (ironically) Ubuntu isn't frozen. And even if it does, it's unresponsive anyway.
    – Stan
    Commented Mar 25, 2014 at 22:07
  • An alternative is to open a terminal and use top from there. Less resource intensive.
    – nocibambi
    Commented May 5, 2021 at 12:00

Freezes such as you have described can be both software and hardware related and as you have found sometimes frustratingly difficult to diagnose.


If this is a desktop PC look at your hardware-cards. For both laptops and desktops possibly acpi type issues.

It might be useful to temporarily simplify your configuration to have just the graphics card connected with a standard keyboard and mouse. All other cards should be removed.

For acpi related issues, try booting with noapic nomodeset in your grub boot option. Its also worth trying acpi=off although this could have other undesirable effects such as constant fan usage.

Also worth checking the bios version level and seeing if the vendor has a newer bios version. The readme notes should hopefully reveal if any newer version fixed crashes and freezes.


I note you have tried the standard 270 drivers but have failed due to freezes. Can you clarify if you had similar issues with the open-source driver? Obviously you will not get Unity during testing this.

Graphics freezing can be one of/or a combination of the driver/compiz/X/kernel

If you are willing to try any of the suggestions below first backup your system with a good backup tool such as CloneZilla. You will need an external media device to receive the image such as a large USB stick/drive or separate internal hard-drive.

Installing newer nVidia driver

Deactivate (uninstall) your current 173-nvidia driver using the Additional Drivers window.

There are a small number of important fixes primarily in the 275 stable but a small number also in the 280beta that fixed freezes - it is worth a shot to see if these apply to your graphics card. Unfortunately nvidia dont go into detail on which cards they specifically fix (readme.txt)

However - I would strongly recommend a backup unless you feel confident on reversing a nvidia install - especially since you had serious issues with the slightly older 270 drivers. I've used clonezilla countless times and it has always got me out of trouble. You do need a large external drive though - USB stick/external drive or a separate drive.

X Updates

The latest graphics drivers have been packaged in the x updates ppa.

Note - this will lead you away from the standard baseline - if upgrading in the future ppa-purge the PPA itself before upgrading.

You can also manually install the drivers from nVidia:

Try installing the latest nvidia stable 275 or 280 drivers - 32bit 280 drivers: ftp site and 64bit: 280 drivers: ftp site

To Install

CTRL + ALT + F1 to switch to TTY1 and login

sudo service gdm stop

To stop the X server

sudo su

To run as root

cd ~/Downloads
sh NVIDIA-Linux-x86-280.04.run

To install the 32bit driver (equiv for 64bit) then reboot.

To uninstall

sudo sh NVIDIA* --uninstall

Also remove /etc/X11/xorg.conf


If you run classic Ubuntu with effects do you get the same freeze issues as standard Ubuntu? If you cannot reproduce the freeze with classic Ubuntu (no effects) then this will point you towards a compiz issue. I would raise a launchpad bug report with the compiz team.

If space is available (e.g. 20Gb), you could dual boot/install alongside the latest oneiric alpha. Obviously this will itself be unstable, but it will come with the latest X and Kernel. You may need to also install manually the beta 280 graphics drivers above since it probably will not be offered in the Additional Drivers window.

If during testing you dont see the same freeze activity you could try uplifting your X version with the x-edgers ppa and using kernel kernel 3.0 in Natty. Going this route is not really desirable - and could cause you upgrade issues in the future - and may have other unforeseen stability issue. Again, use ppa-purge to remove the PPA.

Kernel 3.0 is packaged with the PPA - you'll need to install the headers as well as the kernel itself from synaptic BEFORE rebooting if you intend to install the nvidia drive later.

This is a testing ppa - do have a ready backup if you want to try this route.

  • ... Are you sure this is a good idea, and that it might solve the problem? Or is this just a guess? As I had a lot of trouble with nvidia-current and nothing worked... That's why I switched to the nvidia-173 one. Can I simply restore my whole system from a CloneZilla back-up? The problem is that I haven't got a spare hard drive anymore to put a system copy on...
    – RobinJ
    Commented Aug 12, 2011 at 20:12
  • I'll try... Though I haven't got a hard drive to make a back-up to, so I'll just hope it doesn't break my whole system. About feeling uncomfortable using beta software: I'm working on Ubuntu 11.10 Alpha 3 at the moment xD But for work I just use Ubuntu 11.04 as I don't need constant bugs and sometimes crashes while making a website or something similar :p
    – RobinJ
    Commented Aug 12, 2011 at 21:02
  • Oh dear xD I installed the NVidia-275 driver, and rebooted. X didn't start anymore. No problem, after looking into the log files I saw that another driver was already using the device. I added nouveau to the modprobe blacklist, rebooted, and X started again... But now I've got another problem... I get to see the Unity interface, and then everything simply freezes :p I can switch to the tty's and run commands and everything, but it just seems Unity and the window manager/decorator have crashed. I can't switch back to Gnome Panel (and honestly, I wouldn't want to), ...
    – RobinJ
    Commented Aug 12, 2011 at 21:59
  • ... as I killed it a few weeks ago (on purpose, as it ran together with the Unity Panel for some strange reason :p). And don't tell me to go using Unity 2D please cause it doesn't work too well and easy for me. In fact, Unity is the only reason I still install non-open source drivers. So please help me? xD
    – RobinJ
    Commented Aug 12, 2011 at 22:00
  • ... I already did that, except for re-enabling nouveau as I don't see the use of that. But I meant help me out with the freezing problem please.
    – RobinJ
    Commented Aug 12, 2011 at 23:24

If you're getting a lot of freezes, there might be something wrong with your hardware. I used to get hard lockups every 48 hours due to some less than optimal RAM. Memtest86+ showed the fault after 40 minutes of testing. Swapped the RAM out for some more (under warranty) and I'm now at 32 days, 1 hour of uptime.

Ubuntu doesn't tend to leak its guts all over your memory like Windows can over time. Even if one application or a poor X video driver does, you can restart LigthtDM very simply and just keep going and going and going. I've actually been through three beta versions of the nvidia driver in this one boot :)

Anyway... While knowing how to restart softly is a very handy thing, finding, reporting and fixing the system should be your next priority. If it's an always-on system, you should easily be able to make it between kernel updates* without needing a restart.

*You should restart when you get kernel updates as they'll be security fixes that won't be applied until you reboot into the newer kernel.

  • 1
    I agree that RAM is usually the culprit for unstable systems. I had a problem once that Memtest86+ was not able to found but I could trigger it repeatedly in 5 minutes running sha1sums on very big files repeatedly (checksums changed every now and then). It, too, was fixed by changing memory sticks. Other common causes are unstable power source or poor capasitors on the motherboard. The only way to diagnose these issues is to keep swapping parts until it works. Commented Mar 18, 2014 at 7:34
  • 1
    +1 for memtest86. RAM can be faulty without you really noticing it in daily use.
    – jmiserez
    Commented Jun 24, 2014 at 15:33

When everything stops working, first try Ctrl + Alt + F1 to go to a terminal, where you can likely kill X or other problem processes.

If even that doesn't work, try using holding down Alt + SysReq while pressing (slowly, with a few seconds between each) R E I S U B.

This puts the keyboard in raw mode, ends tasks in various states, syncs the disks, etc, and finally reboots the machine. You will get much better results doing this than just pulling the plug. Of course, if this fails, you're pretty much left with pulling the plug.

  • 12
    A way to remember "REISUB" is "Reboot Even If System Utterly Broken". Commented Sep 20, 2010 at 3:15
  • 8
    or "Raising Elephants Is So Utterly Boring" :P
    – Axel
    Commented Sep 20, 2010 at 12:09
  • 9
    I remember it using "BUSIER" Backwards
    – Nerdfest
    Commented Sep 20, 2010 at 16:33
  • 5
    Between Ctrl+Alt+F1 and trying to kill processes, and Alt+SysRq+R E I S U B, it's worth pressying Ctrl+Alt+Delete. If you successfully got to a text-based virtual console (from having pressed Ctrl+Alt+F1), this will virtually always reboot the machine. Commented Jun 14, 2012 at 21:24
  • Much blunter and in Spanish: REInicia SUBnormal Commented Nov 29, 2013 at 11:16

Also, sometimes it's simply the X-Server which hangs - a case I've most often found when you're using Compiz.

If this is the case you can kill X, which will restart and drop you back at the log-in screen.

The default sequence is Ctrl + Alt + Backspace

Although this is turned off by default (presumably new-users were accidentally hitting it) and can be turned back on like this:

  1. SystemKeyboard (i.e. the Keyboard Preferences Dialogue)
  2. Layouts tab
  3. Click the Options button
  4. At the Key Sequence to kill the X server point check Ctrl + Alt + Backspace.
  • 3
    If your video driver is using kernel modesetting (KMS), it's unlikely this will be sufficient to fix lockups, you have to use sysrq or power cycle. (Go ahead and try C-A-B, it obviously can't hurt; it does work when an app (like compiz/unity) is stuck, rather than X itself, however other answers on this page would be better in this case). But when it doesn't work, now you know why. :-)
    – Bryce
    Commented Jun 16, 2012 at 0:53
  • A note for new users about KMS: As a general rule, if you're using a binary driver (probably if you have an nVidia graphics card, and sometimes if you've got an ATI card) you're video driver is not using KMS. Commented Jun 16, 2012 at 8:53
  • I can't find this in Ubuntu 14.04. When I go to Settings > Keyboard the tabs are only Typing and Shortcuts. I just looked through all the shortcuts and couldn't find "Key sequence to kill the X server". Can I still do this on 14.04?
    – Andy
    Commented Jan 13, 2016 at 12:28

My first favourite when total freeze occured - Alt + SysRq + K.

That combo kills X, and returns me to the graphical login screen. If that doesn't work, try Alt + SysRq + R E I S U B.


What I do is opening a terminal with eg. Ctrl + Alt + F2

Login and use the terminal to kill the process that is lagging

ps -e | grep <procesname>

This shows the processID of the process with that name

(sudo) kill <processID>

This shuts down the process safely, in case that doesn't work use

(sudo) kill -9 <processID>

Use the man pages for more information about these commands.

You can get back to the graphical user interface with Ctrl + Alt + F7

  • 8
    ps and grep PROCESS can be replaced by a pgrep PROCESS call, and your whole thing can simply be replaced by pkill PROCESS or a killall PROCESS. Commented Apr 24, 2011 at 22:01
  • thanks, I didn't know that. Seems to be UNIX commands too, nice
    – Chielus
    Commented Apr 25, 2011 at 8:32
  • However, the default behavior of pgrep is not to show anything but the process ID itself. If you want to know the process's full name and any other information, ps is still a very valuable tool. Commented Jun 14, 2012 at 21:25

In such cases you can try CTRL-ALT-F1 to get to a console. Then login with your password.

Restarting the GUI

You can try to restart your graphical desktop with:

sudo service lightdm restart

If you're running Ubuntu 11.04 or earlier, you should use this instead (as gdm used to be the default display manager):

sudo service gdm restart

If you're using Kubuntu instead, then the default display manager is kdm, so you should instead use:

sudo service kdm restart

If you're using another display manager, replace ligthdm/gdm/kdm with its name.

Restarting the Machine

If you want to do a clean system reboot, use:

sudo shutdown -r now

DoR and Phoenix has answered this well. To make this page more complete I would add:

If it is only X that is "broken", than you can use kernel to kill it:

SysRq + Alt + K

For laptops (depends on the model, typically needed if "SysRq" is written in blue):

Fn + SysRq + Alt + K (release Fn after pressing SysRq).

  • FWIW it depends on the laptop -- on my ThinkPad Alt+SysRq doesn't require Fn nor Ctrl. Commented May 10, 2011 at 12:46
  • 1
    The key pressing sequence is neatly described here (Ubuntu Forums: ubuntuforums.org/showthread.php?p=11773367#post11773367), particulary for laptop where 'Fn' key makes a difference. I had to follow it on my Lenovo Ideapad - hold 'Fn' with left hand first, press Alt + SysRq in right, leave 'Fn' and continue with REISUB slowly.
    – Chethan S.
    Commented Nov 24, 2012 at 16:41

To diagnose the freezes you should be able to use the net console (or serial serial console for that matter). Follow the set up instructions outlined here.

  • I'll give that a shot and post-back the results. Commented Aug 19, 2010 at 22:12
  • This worked like a champ. Identified the problem as my graphics card: "radeon .... reserve failed for wait". Now I know what to look for. Commented Nov 28, 2010 at 21:47

The first thing to look at is if it is just X that's frozen, or the whole system. Enable ssh and then ssh into the system. If you can't ssh into it, then it's probably a kernel lock up. If you can ssh in, then it might be just a gpu lockup.

Next try restarting X. Do this by restarting the display manager:

  • On Ubuntu 11.10 and later, LightDM is the display manager, so run:

    service lightdm restart
  • On Ubuntu 11.04 and earlier, GDM is the display manager, so run:

    service gdm restart

If that works, then it's perhaps an X bug. If it still doesn't work, then you may have a GPU lockup in the kernel drm driver. It would be useful to know at this point whether you're running the -ati (open source) driver, or -fglrx (closed source) driver.

  • 1
    Thanks! My desktop randomly freezes as well. Running 'service gdm restart' always brings it up. Most of the times the desktop seems to freeze when Firefox is running. Any ideas on how I can debug/fix this ?
    – suhridk
    Commented Sep 28, 2010 at 10:35
  • Well, generally when I find myself using the word 'random' in describing a bug, I take that as a clue that I need to do a bit more to better characterize the bug. E.g., how often does it happen, are there any things that seem more likely to trigger it than others, if any other symptoms occur in conjunction, etc.
    – Bryce
    Commented Oct 1, 2010 at 1:28
  • You should also consider your hardware and driver. Some drivers like -intel are more likely to have freeze bugs than other drivers like -ati. Hardware also can play a factor, such as if you put a high end ATI card into a box with a sketchy power supply. Bad RAM, buggy motherboards, overheating, power irregularities, etc. all can result in freezes.
    – Bryce
    Commented Oct 1, 2010 at 1:34
  • Looking through the other commenters on this page, you can see suggestions all over the map. Freezes are an unfortunately common end result of a whole variety of different kinds of problems. They can be software, hardware, or a combination of the two. This is why it is extremely important that the original reporter provide as detailed and thorough a report as possible. This is also why two people both experiencing similar freezes really have to be treated as completely separate bugs, unless their HW and SW are exactly the same.
    – Bryce
    Commented Oct 1, 2010 at 1:41
  • Freezes on different drivers are debugged in different ways. For instance, -intel has a set of debugging tools you can install that allow you to capture GPU dumps. See wiki.ubuntu.com/X/Troubleshooting/Freeze for details.
    – Bryce
    Commented Oct 1, 2010 at 1:42

If you ever use the magic SysRq key as suggested in the first answer, just try getting the keyboard to work first with Alt + SysRq + R; then try Ctrl + Alt + F1 again.

It may work and you may save yourself a reboot. Only if it doesn't work you should try the whole REISUB sequence.


If you have to do a hard shutdown I'd be wondering if the memory (RAM) was failing. On your next boot, try running memtest86. To do this:

  • while booting, hold down a shift key
  • the GRUB menu will appear
  • use the cursor keys to select the last option "memtest86"
  • press enter

You'll get a basic display and it will try reading and writing lots of values to all of your RAM. As long as there are no failures, you'll see a green status. If there is any failure it will turn red. In that case you'll need to replace at least one stick of your RAM.

There is also community documentation of diagnosing hardware failures.


Just press Ctrl + Alt + F1 on your keyboard to open TTY1. When it opens, run the kill command. An example is below.

First you use ps.

This will show you all processes running (ps | less if you want to see the results page by page).
Then you look for the PID of the process you want to terminate. After this use: kill pid

kill command- Stop a process from running

Syntax: kill [-s sigspec] [-n signum] [-sigspec] jobspec or pid kill -l [exit_status]

Description: Most modern shells, Bash included, have a built-in kill function. In Bash, both signal names and numbers are

accepted as options, and arguments may be job or process IDs. An exit status can be reported using the -l option: zero when at least one signal was successfully sent, non-zero if an error occurred. Using the kill command from /usr/bin, your system might enable extra options, such as the ability to kill processes from other than your own user ID and specifying processes by name, like with pgrep and pkill. Both kill commands send the TERM signal if none is given.

Extra: Use Ctrl+Alt+Del for Task Manager in Linux to Kill Tasks Easily

  • 1
    How about if I am not sure about pid which is causing my system to freeze. There could be many processes running interfering with each other making the system freeze. Could you please explain how to tackle in such case.. Commented Jun 12, 2012 at 6:25
  • Using the top command on the console you can often see which process is hanging, by checking the cpu % column. You can then kill that process.
    – Floyd
    Commented Jun 12, 2012 at 8:59
  • What command? ps
    – Mitch
    Commented Jun 12, 2012 at 9:02
  • i meant the command 'top' from the console.
    – Floyd
    Commented Jun 12, 2012 at 9:32
  • As of kinetic 22.10 I had to use CTRL-ALT-F3 to get to terminal. ALT-F2 to return to GUI. Ctrl-Alt-F1 just locked my session. Commented Mar 13, 2023 at 20:58

I thinks there is no such thing as a perfect distro, even in Windows they have this screen of death.

  • Open another terminal Ctrl + Alt + F2.

  • Login with your username and password.

  • Issue this command:

    sudo /etc/init.d/gdm restart

    This restarts or logs you out of your current session but it will not reboot.

Then Ctrl + Alt + F7 go get back to your graphical interface.


You can always do Alt + F2 and write killall <program> or xkill and click on the window you want smashed!


(Community wiki answer - solution was originally buried in the OP question)


Solved it.

My particular problem was my graphics card (integrated Radeon 9000 series). netconsole revealed I was getting the error: "reserve failed for wait". After trial-and-error, I manually configured my video card and disabled hardware acceleration. Completely fixed the issue.

Here is what I did:

Manually Created xorg.conf

Ubuntu automatically configures xorg.conf and doesn't use a file. To edit this file, you have to tell Ubuntu to explicitly create one and then edit it. Here are the steps:

  1. Restart system
  2. Hold Shift as GRUB boots
  3. Select root terminal in GRUB login menu
  4. Execute: X -config xorg.conf.new
  5. Copy: cp xorg.conf.new /etc/X11/xorg.conf

Disable Hardware Acceleration

The following is specific to my Radeon card, but I'm sure other cards have a similar setup.

  1. Edit xorg.conf
  2. Find "Device" section for graphics card
  3. Uncomment "NoAccel" option and set to "True"
  4. Save + reboot

Hope that helps.


Some other resources:


The simplest solution is to add the "Force Quit" applet to your Gnome top panel and when a program doesn't respond, click on the force quit and then on the application.

I am surprised with so many answers, this isn't mentioned. Of course, you can always do a ps -A and pipe that to grep for your program name. And kill -9 that. I prefer simplicity.

  • That's not an option on Unity or GNOME 3 anymore, is it? Commented Aug 16, 2013 at 21:13

You might get some extra information when you switch to the TTY view. Press Ctrl + Alt + F1 to get this, use Ctrl + Alt + F7 (or maybe F8) to get back to the GUI. You can have different sessions on most of the F-keys but that's different question altogether.

  • I tried that but the entire system is locked. Keyboard is completely unresponsive. Commented Aug 19, 2010 at 22:13

My ubuntu is super prone to freezing (probably 20 odd times a day). I use the magic sysrq key too, but instead of using it to reboot or kill xserver, I use the 'f' command which calls oom_kill, effectively dropping a process. I've only ever seen this drop chrome tabs (as I tend to have quite a few heavyweight ones open at a time). Anyway, this get's me out of this mess 95% of the time.

So when my ubuntu freezes (locks up, mouse stops responding etc), I hold alt + sysrq and then hit f (if you don't do this correctly it will take a screenshot instead). I usually have to repeat this combo a couple of times before ubuntu spurs back to life.

I'd have given up on ubuntu a long time ago if I hadn't discovered this, hope it helps someone!


Hit Alt+F2 to run a command. Type xkill and hit Enter.

Your mouse cursor will transform into a cross that can force to close any window you click on.

If somebody can provide a screenshot, I think that would be useful.

  • 2
    not working since the desktop is frozen
    – Floyd
    Commented Jun 12, 2012 at 9:00

There were some missed bugs between the relation of Unity/Compiz, the X.org system and the Video driver. These bugs of course are dealt with with newer, updated versions of Unit, Compiz, X or the video Driver.

When inside Unity and everything is slow and basically damaged, to go to TTY1, press CTRL+ALT+F1. When in the terminal, type your user and password to get to the prompt line. You can also get to the TTY when booting by pressing ESC or holding SHIFT, then on the GRUB menu, selecting recovery mode.

  1. Install Xorg Edgers PPA

    sudo add-apt-repository ppa:xorg-edgers/ppa sudo apt-get update

    Depending on your video card you can either install the 304 series, 310 Series, 313 Series or any newer one that appears there. I recommend always test the latest version and only if it throws a problem, then go down from there until you reach a version where everything works correctly. For example, if you have a GT 9500 or later (Like in my case to which I also have a 440 GT, 560 TI and 680 GTX) the only version that solves all my problems is the 313.18 that came out a couple of days ago. So I would do this:

    sudo apt-get install nvidia-313

    This would install the latest version of the 313 series. It fixes MANY video problems with compiz, unity and xorg. The 310 series also fixes many issues but have not tested that one with my video cards. The other Nvidia versions are nvidia-experimental-304 and nvidia-experimental-310 as of this writing.

  2. Reboot to test if your video card not works correctly with Ubuntu. If you get any problems regarding Nvidia config file, simply open a terminal and type sudo nvidia-xconfig and reboot.

There are other nice questions that could also help like:

How can I update my NVIDIA driver?

How do I install the Nvidia drivers?

Can not install Nvidia driver

What's the difference between the nvidia-current, and nvidia-current-updates packages?

Or even one that is more generic: How to correctly enable Desktop Cube in Unity 3D?


To debug the freeze, you can use Magic SysRq key, for example:

Note: Consider holding ⇧ Shift (depending on your keyboard).

  • Alt-SysRq-9 (no ⇧ Shift) - Set the console log level to 9 to show more of kernel messages
  • Alt-SysRq-w - Display list of blocked (D state) tasks
  • Alt-SysRq-l - Shows a stack backtrace for all active CPUs.
  • Alt-SysRq-t - Output a list of current tasks and their information to the console
  • Alt-SysRq-p - Output the current registers and flags to the console
  • Alt-SysRq-q - Display all active high-resolution timers and clock sources.
  • Alt-SysRq-m - Output current memory information to the console

Other things to try during freeze:

Note: Consider holding ⇧ Shift (depending on your keyboard).

  • Reset the nice level of all high-priority and real-time tasks by hitting Alt-SysRq-n.
  • Try forcing a return to a text console try hitting Control-Alt-F1 (from F1 to F12).
  • Kill all processes on the current virtual console (can kill X) by hitting Alt-SysRq-k.
  • Perform a system crash (if it is configured) by Alt-SysRq-c.

If nothing works, you should perform a safe reboot by Alt-SysRq-REISUB, which is:

  • Alt-SysRq-R: UnRaw (take control of keyboard back from X).
  • Alt-SysRq-E: tErminate (send SIGTERM to all processes).
  • Alt-SysRq-I: kIll (send SIGKILL to all processes, forcing them to terminate immediately).
  • Alt-SysRq-S: Sync all mounted filesystems (flush data to disk).
  • Alt-SysRq-U: Unmount (remount all filesystems in read-only mode),
  • Alt-SysRq-B: immediately reBoot the system.

    Note: If above hard reboot combination won't work, the freeze could be caused by defected hardware, not video drivers.

If you can't use Magic SysRq key, see also: Diagnosing and fixing apparently random Ubuntu crashes?

After reboot, check your kern.log for details, especially call traces generated by above kernel commands. This can help to find the right bug report for it, and find the solution. Check the following kern.log example.

You can check the latest crash log by:

journalctl -b -1 # Then hit Shift-G to jump to the end.

To list other journal logs, run:

journalctl --list-boots

Suggested solution:

  • Upgrade your Ubuntu and kernel to the latest version.
  • If problem repeats, the workaround is to install NVIDIA drivers, which replaces Nouveau video driver.

See also:


I was having similar issues with 10.04. X would hang and and nothing but a reset would fix it. I updated my nvidia drivers to the latest version and I haven't had issues since.

  • Using ATI video drivers...but it might be worth looking into. Thanks! Commented Aug 19, 2010 at 22:13

if possible, try to open an ssh shell from another computer. this is an option If you knew in advance that the computer might hang soon, open the connection first before you perform that task.

I do this sometimes when I know vmware runs crazy and the GUI of ubuntu (the vmware host) becomes unresponsive. I can do a suspend from the ssh shell, it might take a while until it gets thru, and after a while the computer is idle again.

  • A better idea would going to an other TTY (non-GUI) by pressing Ctrl + Alt + F[1-6] where F[1-6] is F1, F2, ..., F6. This is especially helpful if your network connection is heavily used. (to switch back, use Ctrl + Alt + F7. Replace F7 by F8 if it didn't work.
    – Lekensteyn
    Commented Apr 30, 2011 at 8:14
  • Sure, however I always tend to forget these key combinations. And when I know I have to carry out some tasks/experiments where the computer might hang, it's always handy to have access to a second computer available right next to the hanging one.
    – knb
    Commented May 1, 2011 at 13:03
  • For some experiments, a virtual machine in VirtualBox is recommended. In that way, you can easily revert the machines state.
    – Lekensteyn
    Commented May 1, 2011 at 13:24

In the very specific case you are using Virtualbox to run a 64-bit guest on a 32-bit (Ubuntu) host using VT-x or AMD-V (hardware virtualization technology built-in your CPU) only

Virtualbox may make your 32-bit host randomly crash when you run a 64-bit guest on it using VT-x or AMD-V (hardware virtualization technology built-in your CPU). It is a known issue.

2 solutions:

  1. You have to run 32-bit guests only on your current 32-bit host [recommended if you have less than 2 GB of RAM];
  2. You have to switch to Ubuntu 64-bit as host (you can even perform a 32-bit to 64-bit "migration" by reinstalling Ubuntu 64-bit without touching to your "/home" folder) [recommended if you have 2 GB of RAM or more].

Please note that you can run 64-bit and 32-bit guests on a 64-bit host using Virtualbox without any problem.

Other answers have very well covered general cases...


If you have tried all of the above and the freezing problem remains, you might want to try what I did.

Apply generous amounts of contact cleaner to CPU, RAM and any other chip complex enough to show those tiny, tightly packed pins. They can lose conductivity from dust accumulation as well as shorting due to humidity.

Some days after the cleaning (I used CRC 2-26) and a series of really brutal stress tests, my PC hasn't frozen once.

So, for all of you getting sudden unexpected freezings, give up messing around with your OS beyond what's reasonable and do an exhaustive dust and contact cleaning.

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