How can I produce high CPU load on a Linux server?

Question

I’m currently in the process of debugging a Cacti installation and want to create CPU load to debug my CPU utilization graphs.

I tried to simply run cat /dev/zero > /dev/null, which works great but only utilizes 1 core:

enter image description here

Is there a better method of testing/maxing-out system resources under load?

Related: How can I produce high CPU load on Windows?

is it possible to run multiple instances of `cat` simultaneously? — Nate Koppenhaver, Jun 30 '12 at 17:16
@NateKoppenhaver: Yes, that seems to be possible when wrapping them in `screen` sessions. But I would prefer a more sophisticated solution if possible. — Oliver Salzburg, Jun 30 '12 at 17:18
Heh, I always used `cat /dev/random > /dev/null`. Guess `/dev/zero` works too. :-) — oKtosiTe, Jul 01 '12 at 07:25
@oKtosiTe cat /dev/random has the side effect of depleting the entropy in /dev/random. There are times you need to conserve entropy, I wouldn't have this as my go to CPU hog. — Rich Homolka, Jul 25 '12 at 21:41
@oKtosiTe What Rich Homolka said is right, but it's not just that it's a bad thing to do, it's also useless because it'll block almost immediately and stop consuming cpu. — Luc, Jul 22 '14 at 18:11
@Luc This isn't always true. With `haveged` you can create enough entropy. — Stefan, Aug 12 '14 at 12:05
@Stefan Interesting, I didn't know that tool existed. Still, it isn't installed by default on any Debian (based) distribution that I know of. — Luc, Aug 12 '14 at 13:12
I've been using `matho-primes all >/dev/null &` but it's undoubtedly not the BEST answer for everyone. — Wildcard, Dec 19 '15 at 03:00

score 295 · Accepted Answer · edited Nov 17 '20 at 16:42

295

Try stress It's pretty much an equivalent of the Windows consume.exe:

oliver$ ./stress --cpu 3
stress: info: [18472] dispatching hogs: 3 cpu, 0 io, 0 vm, 0 hdd

edited Nov 17 '20 at 16:42

Community

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answered Jun 30 '12 at 17:27

Mitesh Shah

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on ubuntu, you can install with `sudo apt-get install stress` – ben Apr 25 '13 at 17:50
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on debian wheezy too. – enapupe Oct 15 '13 at 01:42
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On Fedora, `sudo yum install stress` – Christopher Markieta Nov 13 '14 at 22:15
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Arch: `sudo pacman -S stress` – das_j Feb 19 '15 at 19:44
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`brew install stress` on OS X – Christian Long Jul 16 '15 at 14:15
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From source: ```wget http://people.seas.harvard.edu/~apw/stress/stress-1.0.4.tar.gz && tar -xvf stress-1.0.4.tar.gz && cd stress-1.0.4 && ./configure && make && sudo make install``` See [README](http://people.seas.harvard.edu/~apw/stress/README). – markdsievers Dec 18 '18 at 02:47
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On Amazon Linux, `sudo amazon-linux-extras install epel -y && sudo yum install stress -y` ([ref](https://gist.github.com/mikepfeiffer/d27f5c478bef92e8aff4241154b77e54)) – Shadi Jul 23 '19 at 08:42
The link to the stress package is dead – Shadi Oct 08 '19 at 12:16
This one worked on Amazon linux EC2 --- sudo yum install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm and then sudo yum install stress -y – oneworld Jun 25 '20 at 00:09
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My choice is the other _one-line solution_ below which does not require any installation: https://superuser.com/a/443633/451797 – Pavan Kumar Sep 15 '20 at 06:32
stress-ng https://github.com/ColinIanKing/stress-ng – ufk Jun 01 '23 at 06:07

jlliagre · Answer 2 · 2019-03-27T11:21:55.180

144

No need to install any extra package, your good old shell is able to do it alone.

This one-liner will load your four cores¹ at 100%:

for i in 1 2 3 4; do while : ; do : ; done & done

How it works is quite simple, it starts four endless loops. Each of them is repeating the null instruction (:). Each loop is able to load a CPU core at 100%.

If you use bash, ksh93 and other shells supporting ranges, (i.e. not dash or older ksh), you can use this non portable syntax:

for i in {1..4}; do ...

Replace 4 with the number of CPUs you'd like to load if different from 4.

Assuming you had no background job already running when you launched one of these loops, you can stop the load generation with that command:

for i in 1 2 3 4; do kill %$i; done

Answering @underscore_d's comment, here is an enhanced version that simplify a lot stopping the load and that also allow specifying a timeout (default 60 seconds.) A Control-C will kill all the runaway loops too. This shell function works at least under bash and ksh.

# Usage: lc [number_of_cpus_to_load [number_of_seconds] ]
lc() {
  (
    pids=""
    cpus=${1:-1}
    seconds=${2:-60}
    echo loading $cpus CPUs for $seconds seconds
    trap 'for p in $pids; do kill $p; done' 0
    for ((i=0;i<cpus;i++)); do while : ; do : ; done & pids="$pids $!"; done
    sleep $seconds
  )
}

¹_{Note that with CPUs supporting more than one thread per core (Hyper-threading), the OS will dispatch the load to all virtual CPUs. In that case, the load behavior is implementation dependent (each thread might be reported as 100% busy or not).}.

edited Mar 27 '19 at 11:21

answered Jul 01 '12 at 14:55

jlliagre

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Thanks, but `&` causes a command to run in a separate _thread_ or separate _core_? I am confused. – mmdemirbas Jul 04 '12 at 14:23
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@mmdemirbas: The ampersand causes the command to run as a separate process. The scheduler is then dispatching all the active processes to all available cores . – jlliagre Jul 05 '12 at 01:54
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As a reminder you can stop this test by issuing `killall bash` - just make sure you don't have any other important script running at the time. – a coder Jun 29 '15 at 19:42
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@acoder Thanks for suggesting a way to end the loop. I would however avoid `killall bash`. Answer edited to add a safer method to end the load generation. – jlliagre Jun 29 '15 at 22:04
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or simply end them with `fg` ctrl+c, 4 times. – phil294 Aug 18 '17 at 17:21
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+1 for the lc shell function – Akira Yamamoto Jun 27 '18 at 07:07
I used this in a script for testing! – Marinaio Aug 12 '19 at 19:28
Thanks for the response. I tried 'for i in 1 2 3 4; do while : ; do : ; done & done'. My question is how to verify/check the CPU load accordingly? I used 'top', however, the % load per each thread is not 100%...Please advise. – Amber.G Jun 23 '20 at 02:02
@Amber.G You can run `htop` as the OP or `mpstat` to see per CPU load. – jlliagre Jun 23 '20 at 07:32
Succinctly, if no other BG jobs are running - `kill $(jobs -p)` – Jack Kinsella Jul 16 '20 at 12:12

rkosegi · Answer 3 · 2017-06-18T08:16:22.770

46

One alternative way would be

openssl speed -multi $(grep -ci processor /proc/cpuinfo)

or (if nproc is present)

openssl speed -multi $(nproc --all)

OpenSSL is almost always present on nowadays distros, so no extra packages needed.

edited Jun 18 '17 at 08:16

answered Sep 08 '16 at 11:19

rkosegi

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imho this should be the accepted answer because it doesn't require any additional packages and it takes care of all cores. – lsu_guy May 24 '23 at 05:03

Pushpak Dagade · Answer 4 · 2013-12-28T08:29:03.210

24

I made a simple python script which does the same. You can control the number of cpu cores you want to load. The good thing about this is that it won't consume any other resource besides the cpu. (I think mark johnson's idea would consume a lot of I/O resources, which is undesired here.)

from multiprocessing import Pool

def f(x):
    # Put any cpu (only) consuming operation here. I have given 1 below -
    while True:
        x * x

# decide how many cpus you need to load with.
no_of_cpu_to_be_consumed = 3

p = Pool(processes=no_of_cpu_to_be_consumed)
p.map(f, range(no_of_cpu_to_be_consumed))

Just run this script from the terminal $ python temp1.py. You need to kill the script when you are done.

Here, is my cpu consumption output when I load 3 of my cores.

Script temp1.py creates three processes (PIDs - 9377, 9378, 9379) which load 3 of my cores

edited Dec 28 '13 at 08:29

answered Jun 30 '12 at 17:56

Pushpak Dagade

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What program do you used to display CPU usage like this? It reminds me of top, but I don't recall the CPU 'charts'. – jftuga Jul 01 '12 at 01:13
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@jftuga probably _htop_, _top_'s prettier brother. – BoppreH Jul 01 '12 at 03:38
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yes its htop. Best real time, colorful interactive process viewer for linux - http://htop.sourceforge.net/ – Pushpak Dagade Jul 02 '12 at 17:12
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Wasn't paying attention and ran this on a Windows box. Very bad things... – Derrick Feb 07 '13 at 17:43

score 20 · Answer 5 · answered Nov 01 '15 at 21:31

20

Start two

sha1sum /dev/zero &

commands for every core in your system.

To stop

killall sha1sum

or

kill sha1sum

answered Nov 01 '15 at 21:31

ecabuk

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Like this one. Short & sweet and didn't need to download anything. – MikeMurko Mar 24 '21 at 03:22

score 11 · Answer 6 · edited Mar 22 '18 at 08:25

11

I've been developing stress-ng, an updated stress tool that can stress a wide range of aspects of a Linux system. For more information, see http://kernel.ubuntu.com/~cking/stress-ng/

Usage is similar to stress

$ stress-ng --cpu 4 --vm 2 --fork 8 --switch 4 --timeout 1m
stress-ng: info:  [32254] dispatching hogs: 4 cpu, 8 fork, 4 switch, 2 vm
stress-ng: info:  [32254] cache allocate: default cache size: 8192K

Install with

sudo apt-get install stress-ng

edited Mar 22 '18 at 08:25

Matt

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answered Sep 06 '15 at 20:11

Colin King

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Please read [How do I recommend software](https://meta.superuser.com/questions/5329/how-do-i-recommend-software-in-my-answers/5330#5330) for some tips as to how you should go about recommending software. At the very least you should provide more than just/at least a link, for example some additional information about the software itself, and how it can be used to solve the problem in the question. – DavidPostill Sep 06 '15 at 20:33

score 7 · Answer 7 · edited Apr 13 '13 at 22:23

I usually take the cpuburn suite:

sudo apt-get install cpuburn
for i in {1..4}; do burnK7 & done

Replace 4 with the number of cores / HT-threads you have or want to stress.

Note: This stresses as much chip area as possible at the same time, it's programmed to generate maximum power dissipation. I had to write this post a second time, somehow my machine didn't like it :-(

You could also do cpuburn in sequences:

burnP6 & burnP6 & burnP6 & burnP6 & 
[1] 28520
[2] 28521
[3] 28522
[4] 28523

And when you want to stop them:

killall burnP6

You could also multiply burnP6 & to match the number of CPU cores on your system.

score 3 · Answer 8 · answered Jul 01 '12 at 02:09

3

You can run that command as many times as you want, and it will take up a different core each time:

$ CORES=1
$ for i in `seq 1 $CORES`; do cat /dev/zero > /dev/null &
> done
[1] 8388

answered Jul 01 '12 at 02:09

Christian Mann

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Wouldn't that make terminating the processes a bit of a hassle? – oKtosiTe Jul 01 '12 at 07:26
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`killall cat` should do it. – Christian Mann Jul 01 '12 at 21:00
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Depending on whether you have other `cat` processes running (I usually do). – oKtosiTe Jul 02 '12 at 13:36

TJR · Answer 9 · 2016-06-22T16:59:30.420

I combined both +jlliagre and +ecabuk.

#!/bin/bash
lc() {
    nowMs=$(date +%s)
    (
        pids=""
        cpus=${1:-1}
        seconds=${2:-60}
        echo "[$(date)] loading $cpus CPUs for $seconds seconds"
        echo "[$(date)] Expected completion: [$(date --date=@$(expr $nowMs + $seconds))]"
        trap 'for p in $pids; do kill $p; done' 0
        for ((i=0;i<cpus;i++)); do
            sha1sum /dev/zero &
            pids="$pids $!";
        done
        sleep $seconds
    )
    echo "[$(date)] Done"
}

lc $@

score 2 · Answer 10 · answered May 17 '19 at 15:33

2

Here's the way I use and there's no need to install anything extra.

For example to start with 4 processes,

nproc | xargs seq | xargs -n1 -P4 md5sum /dev/zero

You can change the number of processes by the option "-P" above.

answered May 17 '19 at 15:33

yichun

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user · Answer 11 · 2016-09-08T11:12:27.250

2

https://github.com/GaetanoCarlucci/CPULoadGenerator

pretty simple and scientific solution.

Here you can see dynamics example in which 50% load is generated on CPU core 0:

You can run the process on other cores at the same time.

edited Sep 08 '16 at 11:12

answered Mar 28 '14 at 15:46

user

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score 1 · Answer 12 · answered Nov 07 '18 at 20:11

pxz is a parallel implementation of xz.

pxz -9e /dev/zero --stdout >/dev/null should do the trick, as this is quite cpu intensive.

If /dev/zero is not fast enough (you notice that pxz gets I/O throttled) you can do pxz -9e /dev/zero --stdout | pxz -9e --stdout >/dev/null

Newer versions of xz have the --threads option which is a substitute for pxz.

AndreasKralj · Answer 13 · 2018-12-11T21:11:36.577

I wanted to add this to @jlliagre's comment, but I don't have enough reputation. If you're going to use this code on multiple servers and the CPU count will vary, you can use the following command:

for ((i=1; i<=`nproc --all`; i++)); do while : ; do : ; done & done

This will utilize all of the cores on your server regardless of how many you have. The command nproc is part of coreutils so should be on most Linux installations.

score 1 · Answer 14 · answered Apr 22 '22 at 06:32

1

Dockerized solution, using stress. Can be deployed using k8s to cover multiple machines.

https://hub.docker.com/r/jfusterm/stress

answered Apr 22 '22 at 06:32

Sida Zhou

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Lyma Lyma · Answer 15 · 2020-05-13T13:31:03.723

1

You can use:

fulload() { dd if=/dev/zero of=/dev/null | dd if=/dev/zero of=/dev/null | dd if=/dev/zero of=/dev/null & }; fulload; read; killall dd

Repeat dd if=/dev/zero of=/dev/null for your CPU cores.

Hit any key to stop the test!

edited May 13 '20 at 13:31

answered Jul 24 '15 at 19:12

Lyma Lyma

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score 0 · Answer 16 · answered Apr 16 '20 at 19:36

0

Run the program stress specifying all the cores you have on your CPU:

stress -c `nproc`

You can get it on Debian/Ubuntu: sudo apt install stress

answered Apr 16 '20 at 19:36

Smeterlink

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score 0 · Answer 17 · answered Jun 30 '12 at 19:08

0

A simple command line does it too:

x="x" ; while : ; do x=$x$x ; echo -n "." ; done

answered Jun 30 '12 at 19:08

ott--

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This would be simpler: `while : ; do : ; done` – jlliagre Jul 01 '12 at 06:30
@jlliagre Yours wön't go above loadavg 1. – ott-- Jul 01 '12 at 11:06
Your loop isn't primarily loading the CPU but more filling the memory. It will eventually crash with an out of memory error. – jlliagre Jul 01 '12 at 12:31
@jlliagre Mine fills memory and swap (if present), thus producing a load of 3 before it killed because it runs out of memory. – ott-- Jul 01 '12 at 14:14
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That's the problem. You aren't answering the question asked which is how to produce a high CPU load on a server. Your script is quickly making a system unresponsive and then crashes. There are much more reliable ways to get a loadavg of 3. eg: `for i in 1 2 3; do while : ; do : ; done & ; done` – jlliagre Jul 01 '12 at 14:52

How can I produce high CPU load on a Linux server?

17 Answers17