script to get 100% cpu/disk usage

sidra · 09-17-2007, 12:16 PM

Hi all,

I want to create a test case by writing a script that will fill up the filesystem and lead to a crash. How can i accomplish this, script code? I also want to try and cause 100% cpu usage, how would i do this?

Thanks in advance.

nadroj · 09-17-2007, 01:37 PM

i thought in order to increase cpu usage/priority you have to have root access (is 100% even possible?). also, i dont know of a way to make such a script, because ive never had to think about it. since this seems malicious, i dont know how much help youll get.

1slipperyfish · 09-17-2007, 02:30 PM

if you're wanting a virus or a virus type of program try some of the hackers forums as they give them out for free, or have i got the question wrong?
paul

gnashley · 09-17-2007, 02:58 PM

Just search this forum for 'fork bomb'. There is at least one thread that discusses them and gives examples.

sidra · 09-17-2007, 04:05 PM

Thanks! I actually filled up disk space very easily, resolved a bug i was working on. Will check out fork bomb!

cconstantine · 09-18-2007, 08:45 AM

super-fast way to fill your drive:

Code:

# cat /dev/null > /some/dir/somefile.txt

/dev/null is implemented within the system so the zero-bytes is produces are super-fast to read by cat. Throughput is limited by your filesystem I/O rate.

jlliagre · 09-18-2007, 03:48 PM

Quote:

Originally Posted by cconstantine

super-fast way to fill your drive:

Code:

# cat /dev/null > /some/dir/somefile.txt

/dev/null is implemented within the system so the zero-bytes is produces are super-fast to read by cat.

You certainly mean /dev/zero, not /dev/null which would just empty somefile.txt.

jlliagre · 09-18-2007, 03:52 PM

Quote:

Originally Posted by nadroj

i thought in order to increase cpu usage/priority you have to have root access (is 100% even possible?).

Actually, assuming your O/S is using a standard scheduler, a very simple script can load a CPU to 100% without any privilege requirements.

For multi-core / multi-thread CPUs, you need to run more than once the script to achieve 100% load.

syg00 · 09-18-2007, 05:14 PM

True, but not much use if you are trying to track interference to some other task - you really need something that isn't as easily pre-empted. I tend to use something like a stress test program - there are a few around.
I also generally use cpusets to contain the test to a subset of CPUs so I can monitor the effect(s) realtime without being locked out myself.

bigearsbilly · 09-19-2007, 04:26 AM

Here is something interesting (?)

it's 2 little perl scripts, one writes to the other through a pipe
something like:

buffer_write.pl -size=10000000 |buffer_read.pl

as the writer doesn't append a newline the reader never reads it.
so the internal buffer fills up and up and up and up.
eventually it fills up, interestingly on linux most often it brings the

OS to it's knees and you get a freeze up. With solaris however it
always chucks you off eventually with: Out of memory!

Code:

#!/usr/bin/perl  -s

# write to the stdout, but with no '\n' character causes
# the internal (stdio?) buffer to fill up.
# when used with the perl buffered <> operation
#
# use -size=n
#
# to increase the write


$main::size ||= 10_000;

$count;

sub do_write {

    $buf = chr int(rand(25)+65);
    $message = $buf x $size;
    $message .= "\n" if $line;;
    print "$message";           # no new line !!!
    $count += length $message;
    warn "$count bytes\n";
}

while ("hell" ne "frozen over") {

    do_write;
}

Code:

#!/usr/bin/perl -n

print length($_), "\n";
print;