Re: can I bring Linux down by running "renice -20 cpu_intensive_process"?

[Jan Engelhardt <jengelh@linux01.gwdg.de>]

>Subject: can I bring Linux down by running "renice -20 cpu_intensive_process"?
>
Depends on what the cpu_intensive_process does. If it tries to allocate 
lots of memory, maybe. If it's _just_ CPU (as in `perl -e '1 while 1'`), 
you get a chance that you can input some commands on a terminal to kill it.
SCHED_FIFO'ing or SCHED_RR'ing such a process is sudden death of course.

> I have a Linux server (kernel 2.6.8.1 + Linux RAID1) which is a "backup"
> machine: it gets the files from other servers, compresses it, writes to the
> tape, checks md5sums etc.
>
> It's been running for quite a bit, no problems with stability so far.
>
Why would you need it to run at -20 anyway?

> As I restarted the machine, I saw that the logging ends few minutes after I
> changed the priority of md5sum to -20.
>
> So here is my question: is it possible to bring down the machine by simply
> doing "renice -20 cpu_intensive_process"?
>
In case of md5sum: it should not be. At least you should have been able to 
unblank the console pressing any key, or have sysrq available.

> As I said, this machine does heavy compression and md5sum calculations of big
> files every day, and was stable all the time - but stopped responding after I
> changed the priority of a CPU-intensive process to -20.
>
> Coincidence and a hardware failure?
>
Sysrq+T (and/or +P) will tell you where the CPU is running.


Jan Engelhardt
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