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I would start by nicing the Xvnc it's only allowed to eat the CPU when other things do not need to run.
It's not a fix but it's a technique I've used to help fix a box that has a run-away process.

The details of how to "nice" it differ between BSD and ATT so do a man nice to find the correct value to use.

Patrick




________________________________
From: Mike Miller <mbmiller+l@gmail.com>
To: VNC List <vnc-list@realvnc.com>
Sent: Tuesday, October 2, 2012 4:11 AM
Subject: CPU at 100%, no refresh, known bug, but what to do?

Here's the bug...

https://bugs.launchpad.net/ubuntu/+source/vnc4/+bug/819473

...and I assume that is what has happened to me.  I'm running Xvnc at 100% CPU and I can connect to it, but the screen won't refresh.  I have a lot of stuff running there and I don't want to kill all of it, so I'm hoping there's some trick to make it refresh again.

Any ideas?

Do I just have to give up and kill Xvnc?

Thanks in advance.

Mike

--
Michael B. Miller, Ph.D.
Minnesota Center for Twin and Family Research
Department of Psychology
University of Minnesota

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On Thu, 4 Oct 2012, Patrick Steranka wrote:

> I would start by nicing the Xvnc it's only allowed to eat the CPU when
> other things do not need to run. It's not a fix but it's a technique
> I've used to help fix a box that has a run-away process.

That's a good idea when there is a single CPU and it's hard to run any
commands because Xvnc is in the way. In my case there are two quad-core
chips so I have 8 CPUs and only one was at 100%, I believe. Anyway, it
was easy to ssh in and do things -- it wasn't slow.

In the end I decided to kill Xvnc, but before I did it I used reptyr to
attach to running ssh jobs and bash shells and exit them properly, saving
the bash command histories. That was great -- I'd never heard of reptyr
until a couple of days ago.

I used ssh to attach to the Ubuntu box with Xvnc running and I ran this
command:

ps aux | grep ssh

That showed me these ssh processes and a few extraneous things:

USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
mbmiller 3520 0.0 0.0 46944 4668 pts/5 S+ Jul25 0:23 ssh -X Server
mbmiller 4602 0.0 0.0 47720 5544 pts/9 S+ Aug09 1:07 ssh -X Server
mbmiller 25614 0.0 0.0 45584 3344 pts/11 S+ Sep24 0:00 ssh -X Server

I launched an xterm from which I would try to recapture those ssh
sessions. I was missing the reptyr binary, so I installed it like so:

sudo apt-get install reptyr

The reptyr man page told me that I had to do this to allow reptyr to work
(I could change the 0 back to 1 after finishing):

$ sudo su
root# echo 0 > /proc/sys/kernel/yama/ptrace_scope
root# exit

After that I just ran reptyr for each process, for example:

reptyr 3520

A few lines of text would appear (the last saying "Set the controlling
tty"), I'd hit "enter" and it would give me my command prompt from my old
shell. I was then able to save command histories, etc.

Mike


> ________________________________
> From: Mike Miller <mbmiller+l@gmail.com>
> To: VNC List <vnc-list@realvnc.com>
> Sent: Tuesday, October 2, 2012 4:11 AM
> Subject: CPU at 100%, no refresh, known bug, but what to do?
>
> Here's the bug...
>
> https://bugs.launchpad.net/ubuntu/+source/vnc4/+bug/819473
>
> ...and I assume that is what has happened to me.  I'm running Xvnc at 100% CPU and I can connect to it, but the screen won't refresh.  I have a lot of stuff running there and I don't want to kill all of it, so I'm hoping there's some trick to make it refresh again.
>
> Any ideas?
>
> Do I just have to give up and kill Xvnc?
>
> Thanks in advance.
>
> Mike
>
> --
> Michael B. Miller, Ph.D.
> Minnesota Center for Twin and Family Research
> Department of Psychology
> University of Minnesota