Easy, Fast, Cheap Way to Generate CPU Load?

jsailor asks: "A large client and their engineering team will be evaluating cabinets and their ability to cool high density blade server deployments. Some of these systems can consume upward of 21 kW per rack and accordingly require a lot of airflow and/or liquid systems to cool. The systems actively monitor heat conditions, increase airflow rates, and can throttle CPU speeds if necessary. What we need is an easy, fast, and cheap way to run the 2-way and 4-way blades at or near peak CPU utilization for extended periods of time so thermal analysis can be performed. Ideally, we would be able to boot them off a CD and have some means of monitoring the CPU on each or even setting the level of CPU utilization we'd like them to run at. Please note that we do NOT need to simulate a real world application and disk and network access are not of much concern. While running your favorite compute-intensive project is a nice idea, we need something simple so I've come to the Slashdot community for assistance. What are your thoughts?"

How about these?

[brejc8]

CPU Burn-in [bigpond.net.au] and cpuburn [sbcglobal.net]

EDIT.COM

[mosel-saar-ruwer]

Back in the day, the old MS-DOS editing program, EDIT.COM, ran a polling loop that would drive the CPU up to 100%.

The Intel guys used to recommend it as a way to stress test your system.

while true; do true; done

[mystran]

That title says it. It's bash syntax. Will give you about 100% CPU utilization on Linux. Run several instances at once to load more CPU's. (while true; do true; done) & (while true; do true; done) & (while true; do true; done) & Since true is /bin/true, each iteration forks twice, which means zero-filling at least a few pages of memory per iteration, which recent Linux AFAIK does with SIMD instructions where possible (someone correct me if that's not correct), so that actually loads more of the CPU core than one would think at first.

Re:while true; do true; done

[12dec0de]

It should read:
while true; do /bin/true; done
otherwise the shell built-in is used and not fork is executed.

Re:while true; do true; done

[mystran]

Indeed, this seems to be true.

I actually tried to check this, but obviously I was too lazy; bash(1) doesn't seem to list true as built-in, but checking (by renaming /bin/true indeed confirms that you are right).

Sorry about that.

Re:while true; do true; done

[harrkev]

Will this generate maximum heat?

I would think that something like Prime95, while larger, would be better.

Your method will exercise a small portion of the ALU. Prime95 will pump up the RAM, and floating-point unit. More transistors switching = more heat!

Re:while true; do true; done

[Spoing]

1. That title says it. It's bash syntax. Will give you about 100% CPU utilization on Linux. Run several instances at once to load more CPU's.

Tried it. Got 30% on one instance and 17% each for up to 8 instances (when I stopped). Plenty of remaining space to run many instances of this loop.

OS & tools: Linux: Fedora Core 3 with latest updates.

Hardware: P4 3ghz with hyperthreading enabled.

Re:That's way too much typing.

[spuzzzzzzz]

First of all, you need to add whitespace in appropriate places (I'm not sure where and I'm not about to test). Your version gives me

-bash: syntax error near unexpected token `{:'

Also you end up running out of memory with all the processes and grinding to a halt as you move to swap space. So CPU utilization is not going to be 100% since you're waiting on the disk.

Re:How about these?

[Anonymous Coward]

The LiveCD List [livecdlist.com] has several bootable CDs which include cpuburn. Check out Stresslinux [stresslinux.org] and Overclockix [octeams.com]. If they don't meet your needs you could modify them.

So simple.

[leonbrooks]

Boot Knoppix, open (BASH) shell, type:

for cpu in 1 2 3 4; do
( while true; do true; done ) &
done

If you want to exercise the disks a bit too, replace the middle line with:

( while true; do find / -type f -exec cp {} /dev/null \; ; done ) &

Re:So simple.

[atomic-penguin]

'while :' is more efficient than 'while true' because you don't have to fork the external process /bin/true. Not sure that your 'for 1 2 3 4' would ever fork more than one process either. Logically this is the same:

while :; do :; done

Unless you can provide some example of true becoming false in the while loop; you would never get 4 forks this way.

Re:So simple.

[lewp]

The parens spawn a subshell. The ampersand at the end backgrounds the subshell. His example is, in fact, right. As far as /bin/true not being as efficient... well, the idea is to load the CPU.

Re:So simple.

[leuk_he]

and for 75% load do:

for cpu in 1 2 3; do
( while true; do true; done ) &
done

SO the parent's solution this is the best solution for this.

Re:How about these?

[GoRK]

I was going to suggest these two tools also. They are specifically designed for what you want to do. I use CPU burn exclusively to test cooling performance in new white box server setups; it is particularly useful in conjunction with lmsensors to determine optimum cooling.

The utility is designed to run instruction loops which require the most POWER CONSUMPTION from the cpu and thus generate the most heat. There are versions tuned from pentiums up to current CPU's. There is also a version designed to cause your ram to use the maximum amount of power it can.

Unlike running any old utility that gives you "100% cpu load" such as the comments about running 'true' in an endless loop presented in this thread, cpuburn is actually targeted at generating heat, power, and system stress. 100% processor utalization does not necessarily mean that you are stressing a computer.

Unsuprisingly, many times cpuburn will often cause a computer that you believe is fine and works properly 100% of the time to hard lock after only a couple of minutes. Over time, dust builds up; fans get slower and give out, etc. and a computer with an adequate cooling solution a year ago may not be able to take the heat anymore. CPUBurn can reveal that. It is a very very good utility.

Linpack

[verycoldpenguin]

On a serious note, linpack ( http://www.netlib.org/linpack/ [netlib.org]) You can run as many processes as required for your machine (i.e. 1 process per cpu) and with care you can use as much memory as you want (memory gets really hot and takes a lot more power than most people think). I do development testing for manufacturers who want us to sell their kit, I have burnt out many (now the manufacturers believe me that they are underspec'd) power supplies by using a well tuned linpack run to overload the system. It will

A Heater.

[Anonymous Coward]

Why not stick a heater in the cabinet that also consumes 21kW of power?

Endless fork?

[mooingyak]

maybe a simple script like:
#!/bin/sh
sh $0

or in c

while ( 1 )
fork();

Re:Endless fork?

[kyle90]

I've been using int main() { while(1); } to stop the Dev-C++ run window from closing as soon as the execution is done - it seems to eat up 100% of my processing power, but dammit, I want to be able to see the results! The only thing it seems to mess up is if I'm listening to music at the time.

Re:Endless fork?

[bigattichouse]

put a sleep(1) in the loop or usleep(100) .. and it won't eat all your CPU

Re:Endless fork?

[flink]

#include <stdio.h>

int main( int argc, const char** argv )
{
/* program */
printf( "\n\nHit any key to quit." );
getchar();
return 0;
}

Flash ads

[BandwidthHog]

Always do it for me. The Vonage ones are the best, especially when you end up with like three of them on a page. Sometimes I swear they can even spike the cpu load of other machines in the same room.

Re:Flash ads

[ErikZ]

My little forum that I run, has a bank of animated GIF smileys you can choose from. When you open the page that gives you all of them at once to pick from, my CPU pegs 100%.

Animated. GIF. Smileys.

Other people use their processing cycles to find puslars. Me? I use mine to have little yellow smiley faces chase each other around with machine guns.

quite simple

[timdorr]

`yes`

A little hack someone showed me a while ago. Just set that in the startup script and away you go! Eats up memory and CPU time, so you'll end up with a very very high load and disk activity to boot.

Re:quite simple

[Student_Tech]

Every time I tried that in a bash shell, it would kill the shell after minute.

So you might want to expand that to
while [ /bin/true ] ; do sh -c '`yes`' ; done

so when this happens:
"sh: xrealloc: ../bash/subst.c:4197: cannot reallocate 268435456 bytes (0 bytes allocated)"

It just restarts it. (Hmm, the comment appears to be formatted correctly for the command).

POVRay

[eskwayrd]

Render something [povray.org]: repeatable, high CPU usage test with visible (and interesting) progress.

Re:POVRay

[Jorkapp]

Or install Folding@Home on all the systems, set the CPU usage to 100%, and set every client to the same User ID and Team. Top user in no time!

here you go

[ArmorFiend]

int main (void)
{
for (int i=0; 1; i++)
;
}

Re:here you go

[p2sam]

boo!! my infinite loop is far superior!!

int main() { for( ;; ) ; }

Re:here you go

[ameoba]

: ( ) { : | : & } ; :

Cat got your tongue? (something important seems to be missing from your comment ... like the body or the subject!)

Re:here you go

[cgenman]

Is it infinitely superior?

Re:here you go

[MerlynEmrys67]

I always prefered
#define ever ;;
int main() {for(ever);}

But again, infinite loops that do nothing tend not to generate significant amounts of heat anyway.

Microsoft's jvc.exe would skip that.

[mosel-saar-ruwer]

Back in the day, Microsoft used to write a nifty little Java "compiler" called jvc.exe [to differentiate itself from Sun's javac.exe] - this was back before Sun sued them over their Java implementation.

Anyway, jvc.exe in combination with Microsoft's java.exe had the uncanny ability to spot empty loops like that and jump write over them.

[Which, no doubt, did not bring pleasure to the ghost of poor ol' Alan Turing...]

Re:Microsoft's jvc.exe would skip that.

[Bert64]

Most modern compilers will do that too, they evaluate if the result from a loop is actually used, and if it isn't, dont bother running it..
Also, if the result is always the same, they will precompute it and remove the loop.

Re:Microsoft's jvc.exe would skip that.

[TheLink]

Ah, but I heard that some modern compilers only remove the loop if it doesn't loop that many times (don't know exact figures). If it loops many times they leave it in.

Because some programmer may be using the loop as a quick and dirty delay.

That's what I heard anyway, haven't bothered testing that.

A DEC ForTran compiler turned one of those...

[leonbrooks]

...benchmarks into a print-string-and-exit monitor call plus a string corresponding to the final answer. This was back in MicroVAX days. Hi, Jeremy!

Re:here you go

[Stevyn]

you might want to throw a float in there too. I'm sure the integer ALU consumes a lot less power than the float ALU. I think something like a video game would also be good for this. It tests integers, floats, and cache. All together, those will generate some serious heat. And since this guy is interested in heat, why not utilize the entire data path plus the cache?

Put your cycles to good use

[Your_Mom]

How about Project Bovine [distributed.net]?

You want load?

[Myrkur]

Post the address on slashdot.

First, make it into a server

[AtariAmarok]

First, make it into a server. Host a web page on it, perferably about a popular topic like Star Wars. Next, successfully submit a Slashdot story that links to it. You'll be overloaded in no time.

Distributed.Net, surely.

[Kris_J]

Distributed.Net [distributed.net] always shows me what happens to a PC permanently at 100% CPU load. Had to remove it from the student labs because it caused all the Dells to turn their fans up full. The noise! There are ports for pretty much everything.

openssl benchmark

[molo]

Fire off one of these per processor:

> while true ; do openssl speed ; done
Doing md2 for 3s on 16 size blocks: 511846 md2's in 3.00s
Doing md2 for 3s on 64 size blocks: 278228 md2's in 3.00s
Doing md2 for 3s on 256 size blocks: 98836 md2's in 3.00s
Doing md2 for 3s on 1024 size blocks: 27645 md2's in 3.00s
Doing md2 for 3s on 8192 size blocks: 3574 md2's in 3.01s
[... continues ...]

-molo

Re:openssl benchmark - SMP version

[Anonymous Coward]

You need to run that on each CPU. This should do it under Linux 2.6:

#!/bin/sh
for x in /sys/devices/system/cpu/*; do
(while true ; do openssl speed; done) &
done
wait

Distributed projects

[OAB_X]

Run seti@home, folding@home, and distributed.net all at once. That should really go for them. Plus they are all linux compatible as well as windows.

Re:Distributed projects

[hcdejong]

Just Folding@home should be enough. The F@h client can be set to use N% of available CPU time (where 0here

Re:Distributed projects

[hcdejong]

that should have read "The F@h client can be set to use N% of available CPU time (where N is between 0 and 100%).
It's available here [stanford.edu]

Gentoo

[dasalvagg]

Finally...a REAL use for Gentoo

Re:Gentoo

[peragrin]

It was my suggestion. se the Gentoo live cd and install to /dev/null of the live cd.

that should keep things busy for a while.

Prime95, as the overclockers use.

[gusnz]

Prime95 [mersenne.org]. Available for numerous OSs.

Re:Prime95, as the overclockers use.

[Craigj0]

This is probably the best as it hits the RAM hard too.

Re:Prime95, as the overclockers use.

[bedessen]

Yes, it will tax the FPU as well as the normal integer units and the cache. The FPU is a considerable amount of die space. Forget all these posts about silly bash fork bombs. Prime95 even has a torture test that you can run in a loop - requires no net connection, no accounts to setup, etc. It's perfect for a boot floopy/live CD.

Infinite loop

[themuffinking]

int main() {
int x=1;
while (1=1) {
x++;
}
return 0;
}

That's one sure fire way to spike CPU usage.

Re:Infinite loop

[pizza_milkshake]

no it's not, try running it. you cannot assign to a constant. i think you mean while(1)

Re:Infinite loop

[thegrassyknowl]

That's not quite the answer. Loading up the CPU to 100% won't guarantee it gets as hot as you would like it too. You need to run CPU instructions that use the most power (floating point, SIMD type instructions, preferably.

Try seti@home or something similar. That would do much more than just a tight - relatively efficient loop.

A

Fractals

[Hadlock]

Some sort of fractal generator, which is avalible on knoppix.

good ol' Hiren's

[Fry-kun]

There's an ISO circulating the net, called Hiren's Boot Disk. It has a lot of utilities for diagnosing and fixing nearly any PC. The only big problem with it is that it's probably less than legal - it has rescue versions of programs such as Partition Magic, Norton Antivirus, etc. It has copies of different burn-in tests (CPU, memory, HD, you name it). Up to you if you want to try it.

And if you don't like that, you can try Knoppix bootable CD. It has (i think) multi-CPU support and you can most likely find

Easy, Fast Way to Generate CPU Load

[Anonymous Coward]

http://www.microsoft.com/windows/ [microsoft.com]

easy as a b C

[hammeredpeon]

while(1) { if(fork() == 0) while(1); } :)

loop.c

[icemax]

void main(void)
{
while(true)
{}
}

Just have it calculate pi...

[Eosha]

Or protein folding@home, or SETI... hell, just fork a bunch of threads each counting to 1,000,000,000...

Come on..

[bloosqr]

this is what I've used to make sure our cluster was cooling properly.. you can even do it in perl.. Of course this won't check to make sure any of your memory is okay or anything else.. but is a simple, straightforward and easy enough to implement..
main() {
a = 0;
for (;;) {
double a;
a *= 1.00001;
}
}

Re:Come on..

[cnvogel]

fredegar vogel $ cc -Wall -g slashdot.c
slashdot.c:1: warning: return type defaults to `int'
slashdot.c: In function `main':
slashdot.c:2: error: `a' undeclared (first use in this function)
slashdot.c:2: error: (Each undeclared identifier is reported only once
slashdot.c:2: error: for each function it appears in.)

Re:

[account_deleted]

Comment removed based on user account deletion

How about Netbench?

[msoftsucks]

A few years back Ziff Davis released some decent benchmarking tools. The ones for file serves were called Netbench [etestinglabs.com] You can set up different tests that exercise different aspects of file servers. With just a couple of PCs you can create significant load that would peg the CPU utils to 100% for a whole weekend. Although these tools are no longer supported, they still work quite well.

LAPACK et. al.

[Salis]

LAPACK or LABLAS linear algebra libraries

That's what they use to spec and rank supercomputers. It'll burn, burn, burn!

Re:LAPACK et. al.

[Salis]

Uhh.... LAPACK [netlib.org].

LinPack [netlib.org] also exists. From Linpack's website, "LINPACK was designed for supercomputers in use in the 1970s and early 1980s. LINPACK has been largely superceded by LAPACK, which has been designed to run efficiently on shared-memory, vector supercomputers."

But, dude, why the hate? These are subroutines that solve specifically defined linear algebra problems. They happen to consume a large amount of cpu time for large scale problems. So why the reply? Or are you just trying to flamebait?

Re:LAPACK et. al.

[Salis]

Um. Linpack is ALSO a linear algebra library.

It's the older one. LAPack is the newer one. I still don't understand why you're ranting about this.

Uh, the program could be very simple. Create a randomized A matrix (1 million x 1 million). Create a randomized b matrix (1 million). Solve for x, Ax=b, using LAPACK. If that's too difficult for the guy, then maybe he shouldn't be in charge of a major computing center. Or he can tell someone else to do it.

Solving it (using Gaussian elim or another of LAPACK's su

Re:LAPACK et. al.

[Salis]

For someone who knows all this, you didn't know what LAPACK was.

And the reason why you chimed in is because you're probably bored, an **hole, and have nothing else to do.

My last reply.

Merseinne Prime

[Xife]

At one time I heard Intel used this because it was real good at filling up the CPU pipelines.

Seti@Home is another alternative along the same lines, although Seti will utilize more Hard drive. (Signal processing vs huge Mathematical algorithm).

The Ultimate Bootable CD

[DustMagnet]

Since you said you'd like a bootable CD for your load, I'd recommend The Ultimate Bootable CD (UBCD). The UBCD has memtest and some other utilities that will stress the CPU. It has dozens of other utilities that you'll love.

Burn it to a DVD and it will load even faster.

md5sum

[jacobdp]

md5sum < /dev/urandom

/dev/urandom produces an infinite stream of random data - just pipe that throgh MD5 for some nice numerical CPU load. Not disk- or network-bound either.

Re:md5sum

[boneshintai]

Reading /dev/urandom does not block when the system runs low on entropy -- it just keeps producing "random" noise that gets less random. This property makes /dev/urandom unsuitable for real crypto use, where you want /dev/random's entropy guarantees. Read the man page on random(4) for more info.

Remember the disks too

[gtrubetskoy]

Disk drives generate heat (and fail first from it). To keep your drives excercised, check out Bonnie [garloff.de].

This is easy

[crmartin]

cat > swamp.c
int main(){ for(;;) ; }
^D
gcc -o swamp swamp.c
sudo nice -20 ./swamp

100 percent CPU load, nice as you please.

Easiest way

[PKPerson]

Try running windows

Re:Easiest way

[Glytch]

Oh, Slashdot, why are you so placid and intolerant of a good old-fashioned flamewar these days? I had to scroll through two pages of boring serious answers before finding this, the proper reply to this story.

bc and ^

[ubiquitin]

bc
1234123412341234^1234123412


Should work for at least an hour or two on current CPU's.

gzip

[CyberVenom]

So you need simple, fast, no-need-for-network CPU load?

Boot any linux liveCD that supports your hardware, and run the following command:

cat /dev/urandom | gzip > /dev/null

Sould eat one whole CPU and run forever. If you have an SMP machine, run one instance of that per CPU, and you should max out. The system should still remain responsive enough that you can terminate the processes at will, even though the CPU is at 100% usage.

I would try to pick a liveCD that does not bother starting X since that just adds to the boot time.

You may want to consider the heat generated by components other than the CPU. Hard drives put off a significant amount of heat, as do memory and video, and to a lesser extent network hardware.

To utilize a lot of memory as well as CPU, you might look for something like a prime-factoring program. (prime seives love to eat memory)

For video heat, try something like an unlimited framerate demo in Quake 2. (I think there is even a Linux port)

For network load, just use a ping utility that supports flood-ping and arbitrary payloads. Then floodping yourself or something on the LAN with huge packets.

For hard drive heat, you could just dd /dev/zero to a blank HD (since you are booting from CD, destroying the contents of the HD won't crash the OS)

Another option

[chriskenrick]

There are some CPU spinners in the CPU scheduler evaluation [sourceforge.net] project that should be of assistance.

The actual download page is here [sourceforge.net]

Kernel compiles!

[itwerx]

Can't believe nobody's suggested just doing kernel compiles in a loop...?

Re:Kernel compiles!

[menscher]

Can't believe nobody's suggested just doing kernel compiles in a loop...?

I was about to, and saw your post when making sure I wouldn't be modded redundant. It's the best method I've found to stress-test your CPU and memory subsystem. In particular, do a make -j to compile in parallel, and use all your CPUs. Be careful, though, the 2.6 kernel will drive your load up to about 80 if you don't restrict it.

I've previously used the kernel-compile trick to test processor stability (when overclocking). Comp

Re:Kernel compiles!

[menscher]

Huh? Just to prove you wrong, I downloaded the latest kernel (2.6.11.7) and started a make -j on it. Top showed 80% usr, 20% sys. So io/wait was down under 1%. Cool part was the load average shooting up over 3000. Then top stopped refreshing, and I can't seem to ssh in anymore. Oops.

For the curious, this was on a dual opteron with 8 gig of ram.

Ah, doing a ^C got it back... here's top output on its way down:

top - 00:12:04 up 12 days, 19:09, 16 users, load average: 592.34, 743.33, 647.93
Tasks: 453

Re:Kernel compiles!

[itwerx]

...a dual opteron with 8 gig of ram.

Damn you!
And here I'd just convinced myself I didn't *really* need to upgrade my main test system yet!
Argh... :)

Slashdot community is simple

[DaoudaW]

we need something simple so I've come to the Slashdot community for assistance.

Thanks! I think...

Folding@HOME!

[xmas2003]

The powder2glass team is #4 for Google Toolbar Compute folks [powder2glass.com] - we'd love to get some boost in our ranking if you want to fire up FAH and contribute some work units. Note that you can use the FAH client from Stanford [stanford.edu] and we'll still get some credit if you team=0, and username=powder2glass.

Sounds like you got some serious, serious horsepower, so I can't resist asking! ;-)

It's not so easy

[Phil Karn]

I don't think it's quite as easy as running a simple infinite loop. That will certainly peg the CPU utilization at 100%, but it probably won't maximize the power drain and heat output.

Modern CPUs are complicated beasts, with multiple execution units, deep pipelines and big caches. And they're connected to big external memories and disk drive arrays. If you want to stress-test the cooling system, then you need code that keeps all the execution units and all the pipelines and the caches and main memory and the disk array all going full blast. That's not as easy as it sounds. Intel has mentioned various test programs that they use when thermally testing their CPUs, but I don't know that they've ever released them. Perhaps they're afraid they'd might cause damage, and they'd have to deal with a lot of irate customers.

Re:It's not so easy

[Phil Karn]

Sounds like that would quickly become highly I/O bound, and CPU utilization would be nearly zero.

Again, these things have to be carefully constructed to load up everything. It's almost impossible in any real application -- something always seems to bottleneck well before everything else -- and with the architectural complexities of today's CPUs, probably only a little easier to do in a test designed merely to load everything up without accomplishing any useful work.

Goin for da gold

[termos]

yes|grep no

Perl

[VenTatsu]

perl -e "for(2..$ARGV[0]){last unless fork}print$$,$/;sqrt(rand(1<<32))while 1"

This will suck up all the CPU for one processor, add the number of processes to run on the end of the command line to load multiple CPUs.

Simulations

[flikx]

I have a few simulations that are taking upwards of 48 hours each to run on puny Athlon 1300s. I could load your systems for a couple hours. :-)

Easy, CPUBurn

[Lomby]

Download CPUBurn here [sbcglobal.net].
Run x instances, where x is the number of CPUs in your machine.
As easy as that.

small, cool, little iso

[LordAlpha]

- Minimal linux distribution running from a bootable cdrom or via PXE.

- Uses of some utitlities like: stress, cpuburn, hddtemp, lm_sensors, smartmontools .

- Dedicated to users who want to test their systems entirely on high load and monitoring their health.

http://www.stresslinux.org/ [stresslinux.org]

You need stress

[Dysan2k]

There's a software package called 'stress' that should fill your needs nicely.

http://weather.ou.edu/~apw/projects/stress/ [ou.edu]

I use it at work for testing all of our servers. You have the option of testing CPU, Memory, IO, or VM, and it will most certainly put a heavy load on the server.

File compression

[Lehk228]

run 7zip compressing a very large file to 7z format in ULTRA mode, large file being CD ISO sized or so. either that or video encoding, but video encoding has been improved greatly over the years while 7z ULTRA mode is basically designed to not care about resource usage and squeeze an extra 2 megs off a 5 gig DVD image even if it takes 3 more hours to do it. (BTW, ULTRA is amazing with game compression, HL2 in 1.5 gigs anyone?)

It was so obvious and I missed it.

[bigattichouse]

Add a link to your servers, and post a front page link on slashdot!

AMD-based solution

[Donny Smith]

Here's an idea for you:
1. Get 10-20 older Athlon boxes.
2. Put them in the same room with the blade servers you want to test.
(3. And do I need to add this step - profit!)

Re:Fact(-1)

[SomeGuyFromCA]

er.

if memory serves, factorial(x) is undefined on x (unsigned int) -1 wouldn't take a nice long time...

Re:hmmph

[menscher]

Actually, factorial(x) is defined as gamma(x+1). And the gamma function is defined for negative values of x also. So computing the "factorial" of a negative number isn't really a problem.

Re:hmmph

[menscher]

Yes... though it blows up for non-positive integers. See mathworld [wolfram.com] for details.

Re:Here's a good one...

[LuckyStarr]

Better use /dev/zero or /dev/urandom as /dev/random may not provide characters fast enough to be of any use (heating).

Re:infinite loop in java

[Tet]

Who needs an infinite loop? Just running running any java program should be enough to consume all of your CPU cycles and bring the system to its knees...