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I'm doing some testing on a Linux server and I need the server to be on a heavy load. I was wondering how I would simulate this? Right now the server goes upto 20% CPU but I need to force it to around 80% and do some testing to see how it copes.

unleashed
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2 Answers2

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If you want to force CPU's occupation, try this : 

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

If you want to simualte IO charge too, try with this :

for cpu in 1 2 ; do
   ( while true; do find / -type f -exec cp {} /dev/null \; ; done ) &
done

with for cpu in 1 2 for 2 cores, for cpu in 1 2 3 4 for 4 cores ;)

Cédric Julien
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  • I'm guessing this does some searching or something in dev/null ? – unleashed May 19 '11 at 09:28
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    the `find` command with those arguments are copying every file in the filesystem to `/dev/null`, so generating a lot of IO as @Cédric said. – Carlos Campderrós May 19 '11 at 09:37
  • Certainly works although i'm abit worried with the copying of files to /dev/null. The files don't actually get permanently stored in /dev/null right? – unleashed May 19 '11 at 09:47
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    @unleashed no, `/dev/null` is some kind of black-hole or sink. Anything you store in there just disappears, and does not use a single byte of your hard disk space. – Carlos Campderrós May 19 '11 at 09:54
  • find generates a lot of file system i/o. But @unleashed like to know, how to rise the CPU usage much as possible. So don't use filesystem-components for that, because the CPU generates filesystem-wait-i/o which is not the same as CPU usage. – The Bndr May 19 '11 at 12:58
  • @The Bndr : my first loop burn only CPU, my second loop burn IO (if your filesystem are in a RAMFS, it will burn some CPU too), if you want to burn CPU and IO, launch the 2 loops in parallel ;) – Cédric Julien May 19 '11 at 13:01
  • @Cédric Julien Sorry, I did an mistake be reading your post. So: everything is fine. Sorry. :-) – The Bndr May 19 '11 at 13:18
  • To kill them, use `kill %1 %2`, replacing the numbers with the ones printed at the beginning of the lines when starting the jobs. – l0b0 Apr 07 '14 at 10:18
  • Copying a file to /dev/null overwrites /dev/null. – Felipe Alvarez Jun 16 '16 at 22:50
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If you are looking for generating cpu usage, so you have to choose commands, which are CPU intensive. For example generation random-numbers.

Try this:

dd if=/dev/urandom of=/dev/null

Add on of those line for every CPU core. If you have an dual-core CPU use:

dd if=/dev/urandom of=/dev/null &
dd if=/dev/urandom of=/dev/null &

Check the jobs with

jobs

End the jobs with kill %1 (where %1 is the number of job 1)

The Bndr
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