RE: What should I do when Ubuntu freezes?

**MeanRoy** · February 7th, 2014

I find in http://askubuntu.com/questions/4408/...ubuntu-freezes

For a fully locked up system (mouse unresponsive) during a Firefox session, I found the following directions:

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

REISUB by:

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

The problem I find with this is that pressing Alt and the SysReq (Print Screen) initiates a screen capture.
Well actually a bunch due to KB repeat feature.

What am I not understanding here?

This is pretty important to me as I just went through a lengthy adventure with downloading an Ubuntu iso, booting livedisk, open term window, run fsck, correct a lengthy set of problems, and very luckily successfully re-boot.

All because Firefox froze the system and I had to hard reset the system.
I've had to do this before and didn't have a problem but once was more than enough thank you very much!

Roy

**tgalati4** · February 7th, 2014

Normally your system will do a couple of things during a freeze: The Caps Lock and Num Lock keys will flash--which is kind of scary looking or you will get no indication and nothing you do will revive the system--including the "magic keys". If you get a screen shot, then that means your system is not really frozen. Try going to another window (Control-Alt-Right_Arrow) and see if it switches. If so, then you can open a terminal and:

Code:

sudo killall firefox

The Alt-Shift-SysRq AND R--E--I--S--U--B (one or two seconds between each key) will cause various things to happen, the most important being synchronize the disks (S) and then Reboot (B). This prevents disk errors and having to wait for a file system check (fsck) upon the next boot cycle. I find about 50% of freeze ups can be rebooted this way. I haven't experienced many in 8 years of using Ubuntu.

Firefox might have a busted profile. Try clearing cache, history, etc. Open a terminal and run firefox in it. Watch for errors that scroll by in the terminal.

**egeezer** · February 7th, 2014

But if you really get into a bind, you need to check if your SysRq key is properly activated. Run:

Code:

cat /proc/sys/kernel/sysrq

If it returns 1, it's working its magic. If it returns 0, it isn't

To activate:

Code:

sudo echo "1" > /proc/sys/kernel/sysrq

**MeanRoy** · February 7th, 2014

Thanks very much for the replies.
I accidentally mislead you, after fixing the problems I tried this to make sure I knew how it worked. The system wasn't frozen when I did this.
On reading your reply though, I see where I messed up!
I failed to hold the shift as well.

I just knew it was something dumb.

I'll do the check to be sure the SysRq key is working properly and re-try the technique.

I don't think my firefox is hosed, I think some javascript stuff in conjunction with youtube ties up all the resources and *might* eventually return control. I do wonder about how this happens though.

Roy.

**tgalati4** · February 8th, 2014

Run Adblock Edge and Noscript and that should take care of the bad actors. The magic sequence should still reboot the system even if it is not frozen. Make sure all of your applications are closed. You don't want to lose any data during a rapid shutdown.

**ajgreeny** · February 8th, 2014

Use the right hand Alt + Print-Screen, not left had Alt.

**MeanRoy** · February 8th, 2014

Ok guys, that does it, works fine.
Someone should make the correction to add the shift key to the instructions in http://askubuntu.com/questions/4408/...ubuntu-freezes

Thanks very much!

Roy