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

cat /dev/urandom > /dev/null

Answer 2

I use stress for this kind of thing, you can tell it how many cores to max out.. it allows for stressing memory and disk as well.

Example to stress 2 cores for 60 seconds

stress --cpu 2 --timeout 60

Answer 3

Utilizing ideas here, created code which exits automatically after a set duration, don't have to kill processes --

#!/bin/bash
echo "Usage : ./killproc_ds.sh 6 60  (6 threads for 60 secs)"

# Define variables
NUM_PROCS=${1:-6} #How much scaling you want to do
duration=${2:-20}    # seconds

function infinite_loop {
endtime=$(($(date +%s) + $duration))
while (($(date +%s) < $endtime)); do
    #echo $(date +%s)
    echo $((13**99)) 1>/dev/null 2>&1
    $(dd if=/dev/urandom count=10000 status=none| bzip2 -9 >> /dev/null) 2>&1 >&/dev/null
done
echo "Done Stressing the system - for thread $1"
}


echo Running for duration $duration secs, spawning $NUM_PROCS threads in background
for i in `seq ${NUM_PROCS}` ;
do
# Put an infinite loop
    infinite_loop $i  &
done

Answer 4

I've used bc (binary calculator), asking them for PI with a big lot of decimals.

$ for ((i=0;i<$NUMCPU;i++));do
    echo 'scale=100000;pi=4*a(1);0' | bc -l &
    done ;\
    sleep 4; \
    killall bc

with NUMCPU (under Linux):

$ NUMCPU=$(grep $'^processor\t*:' /proc/cpuinfo |wc -l)

This method is strong but seem system friendly, as I've never crashed a system using this.

Answer 5

One core (doesn't invoke external process):

while true; do true; done

Two cores:

while true; do /bin/true; done

The latter only makes both of mine go to ~50% though...

This one will make both go to 100%:

while true; do echo; done

Answer 6

To load 3 cores for 5 seconds:

seq 3 | xargs -P0 -n1 timeout 5 yes > /dev/null

This results in high kernel (sys) load from the many write() system calls.

If you prefer mostly userland cpu load:

seq 3 | xargs -P0 -n1 timeout 5 md5sum /dev/zero

If you just want the load to continue until you press Ctrl-C:

seq 3 | xargs -P0 -n1 md5sum /dev/zero