How to create a CPU spike with a bash command

Question

I want to create a near 100% load on a Linux machine. It\'s quad core system and I want all cores going full speed. Ideally, the CPU load would last a designated amount of

Answer 1

This does a trick for me:

bash -c 'for (( I=100000000000000000000 ; I>=0 ; I++ )) ; do echo $(( I+I*I )) & echo $(( I*I-I )) & echo $(( I-I*I*I )) & echo $(( I+I*I*I )) ; done' &>/dev/null

and it uses nothing except bash.

Answer 2

I combined some of the answers and added a way to scale the stress to all available cpus:

#!/bin/bash

function infinite_loop { 
    while [ 1 ] ; do
        # Force some computation even if it is useless to actually work the CPU
        echo $((13**99)) 1>/dev/null 2>&1
    done
}

# Either use environment variables for DURATION, or define them here
NUM_CPU=$(grep -c ^processor /proc/cpuinfo 2>/dev/null || sysctl -n hw.ncpu)
PIDS=()
for i in `seq ${NUM_CPU}` ;
do
# Put an infinite loop on each CPU
    infinite_loop &
    PIDS+=("$!")
done

# Wait DURATION seconds then stop the loops and quit
sleep ${DURATION}

# Parent kills its children 
for pid in "${PIDS[@]}"
do
    kill $pid
done

Answer 3

Here is a program that you can download Here

Install easily on your Linux system

./configure
make
make install

and launch it in a simple command line

stress -c 40

to stress all your CPUs (however you have) with 40 threads each running a complex sqrt computation on a ramdomly generated numbers.

You can even define the timeout of the program

stress -c 40 -timeout 10s

unlike the proposed solution with the dd command, which deals essentially with IO and therefore doesn't really overload your system because working with data.

The stress program really overloads the system because dealing with computation.

Answer 4

Dimba's dd if=/dev/zero of=/dev/null is definitely correct, but also worth mentioning is verifying maxing the cpu to 100% usage. You can do this with

ps -axro pcpu | awk '{sum+=$1} END {print sum}'

This asks for ps output of a 1-minute average of the cpu usage by each process, then sums them with awk. While it's a 1 minute average, ps is smart enough to know if a process has only been around a few seconds and adjusts the time-window accordingly. Thus you can use this command to immediately see the result.

Answer 5

#!/bin/bash
duration=120    # seconds
instances=4     # cpus
endtime=$(($(date +%s) + $duration))
for ((i=0; i<instances; i++))
do
    while (($(date +%s) < $endtime)); do :; done &
done