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 time and then stop   I m hoping there s some trick in bash   I m thinking some sort of infinite loop

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Although I m late to the party  this post is among the top results in the google search  generate load in linux    The result marked as solution could be used to generate a system load  i m preferring to use sha1sum  dev zero to impose a load on a cpu-core    The idea is to calculate a hash sum from an infinite datastream  eg   dev zero   dev urandom       this process will try to max out a cpu-core until the process is aborted  To generate a load for more cores  multiple commands can be piped together    eg  generate a 2 core load   sha1sum  dev zero   sha1sum  dev zero

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bin bash duration 120      seconds instances 4       cpus endtime      date   s     duration   for   i 0  i lt instances  i     do     while     date   s   lt   endtime    do    done  amp  done

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Just paste this bad boy into the SSH or console of any server running linux   You can kill the processes manually  but I just shutdown the server when I m done  quicker   Edit  I have updated this script to now have a timer feature so that there is no need to kill the processes   read -p  Please enter the number of minutes for test  gt   MINTEST  amp  amp      MINTEST      -    0-9       NCPU    grep -c  processor  proc cpuinfo       endtime   date   s      MINTEST 60     NCPU    NCPU-1    for   i 1  i lt   NCPU  i      do while     date   s   lt   endtime    do     done  amp  done

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bin bash while   1   do          Your code goes here done

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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

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To load 3 cores for 5 seconds   seq 3   xargs -P0 -n1 timeout 5 yes  gt   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

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I would split the thing in 2 scripts    infinite loop bash       bin bash while   1     do       Force some computation even if it is useless to actually work the CPU     echo    13  99   1 gt  dev null 2 gt  amp 1 done   cpu spike bash       bin bash   Either use environment variables for NUM CPU and DURATION  or define them here for i in  seq   NUM CPU     do       Put an infinite loop on each CPU     infinite loop bash  amp  done    Wait DURATION seconds then stop the loops and quit sleep   DURATION  killall infinite loop bash

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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

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An infinite loop is the idea I also had  A freaky-looking one is   while    do    done      is the same as true  does nothing and exits with zero   You can call that in a subshell and run in the background  Doing that  num cores times should be enough  After sleeping the desired time you can kill them all  you get the PIDs with jobs -p  hint  xargs

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cat  dev urandom  gt   dev null

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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

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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

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I think this one is more simpler  Open Terminal and type the following and press Enter   yes  gt   dev null  amp    To fully utilize modern CPUs  one line is not enough  you may need to repeat the command to exhaust all the CPU power   To end all of this  simply put  killall yes   The idea was originally found here  although it was intended for Mac users  but this should work for  nix as well

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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 gt  dev null 2 gt  amp 1     done      Either use environment variables for DURATION  or define them here NUM CPU   grep -c  processor  proc cpuinfo 2 gt  dev null    sysctl -n hw ncpu  PIDS    for i in  seq   NUM CPU     do   Put an infinite loop on each CPU     infinite loop  amp      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

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amp        This fork bomb will cause havoc to the CPU and will likely crash your computer

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This does a trick for me   bash -c  for    I 100000000000000000000   I gt  0   I        do echo     I I I     amp  echo     I I-I     amp  echo     I-I I I     amp  echo     I I I I      done   amp  gt  dev null   and it uses nothing except bash

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to increase load or consume CPU 100    sha1sum  dev zero  amp    then you can see CPU uses by typing command   top   to release the load   killall sha1sum

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I ve used bc  binary calculator   asking them for PI with a big lot of decimals     for   i 0 i lt  NUMCPU i     do     echo  scale 100000 pi 4 a 1  0    bc -l  amp      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

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You can also do  dd if  dev zero of  dev null   To run more of those to put load on more cores  try to fork it    fulload     dd if  dev zero of  dev null   dd if  dev zero of  dev null   dd if  dev zero of  dev null   dd if  dev zero of  dev null  amp     fulload  read  killall dd   Repeat the command in the curly brackets as many times as the number of threads you want to produce  here 4 threads    Simple enter hit will stop it  just make sure no other dd is running on this user or you kill it too

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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   lt   endtime    do      echo   date   s      echo    13  99   1 gt  dev null 2 gt  amp 1       dd if  dev urandom count 10000 status none  bzip2 -9  gt  gt   dev null  2 gt  amp 1  gt  amp  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   amp  done

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To enhance dimba s answer and provide something more pluggable  because i needed something similar    I have written the following using the dd load-up concept  D  It will check current cores  and create that many dd threads  Start and End core load with Enter     bin bash  load dd         dd if  dev zero of  dev null    fulload         unset LOAD ME UP SCOTTY     export cores    grep proc  proc cpuinfo -c       for i in    seq 1    expr  cores - 1           do     export LOAD ME UP SCOTTY    LOAD ME UP SCOTTY   echo  load dd         done         export LOAD ME UP SCOTTY    LOAD ME UP SCOTTY   echo  load dd  amp         eval   LOAD ME UP SCOTTY     echo press return to begin and stop fullload of cores   read   fulload   read   killall -9 dd

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Using examples mentioned here  but also help from IRC  I developed my own CPU stress testing script  It uses a subshell per thread and the endless loop technique  You can also specify the number of threads and the amount of time interactively      bin bash   Simple CPU stress test script    Read the user s input echo -n  Number of CPU threads to test    read cpu threads echo -n  Duration of the test  in seconds     read cpu time    Run an endless loop on each thread to generate 100  CPU echo -e   E 32mStressing   cpu threads  threads for   cpu time  seconds    E 37m  for i in   seq   cpu threads    do     let thread   i -1      taskset -cp   thread   BASHPID  while true  do true  done   amp  done    Once the time runs out  kill all of the loops sleep   cpu time  echo -e   E 32mStressing complete  E 37m  kill 0

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I went through the Internet to find something like it and found this very handy cpu hammer script      bin sh    unixfoo blogspot com  if    1    then     NUM PROC  1 else     NUM PROC 10 fi  for i in  seq 0    NUM PROC-1     do     awk  BEGIN  for i 0 i lt 10000 i   for j 0 j lt 10000 j        amp  done

[linux] How to create a CPU spike with a bash command

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