dd usage

shlomo.hovir · 10-14-2018, 07:59 AM

i posted before a question on reddit about how to stress test a cpu someone recommended me a command dd i knew that he is trying to burn my computer he gave me overrated values can someone explain me bs and count usage because even using manual pages i couldn't understand them and what's the maximum values to test on

bs=BYTES
read and write up to BYTES bytes at a times
count=N
copy only N input blocks

FlinchX · 10-14-2018, 08:41 AM

dd is for copying files, it has nothing to do with stress testing a cpu

when used improperly, it can ruin your filesystems indeed

what exactly do you mean by stress testing a cpu anyway?

shlomo.hovir · 10-14-2018, 09:42 AM

Quote:

Originally Posted by FlinchX

dd is for copying files, it has nothing to do with stress testing a cpu

when used improperly, it can ruin your filesystems indeed

what exactly do you mean by stress testing a cpu anyway?

overload cpu with random data came from /dev/urandom

berndbausch · 10-14-2018, 10:22 AM

Quote:

Originally Posted by shlomo.hovir

bs=BYTES
read and write up to BYTES bytes at a times
count=N
copy only N input blocks

bs is block size, count is number of blocks. For example, with bs=1024k and count=100, dd will copy 100 1MB-blocks from input to output.

While I don't know what exactly you want to test, a simpler way of loading the CPU is to run a few yes coommands:

Code:

for i in {1..20}
do
    yes >/dev/null &
done

FlinchX · 10-14-2018, 11:29 AM

Quote:

Originally Posted by shlomo.hovir

overload cpu with random data came from /dev/urandom

I don't understand

kilgoretrout · 10-14-2018, 11:51 AM

There are specific tools for stress testing in linux, namely stress and stress-ng. They're generally available on most distros. See:

https://linux.die.net/man/1/stress

http://www.ubuntugeek.com/stress-ng-...tu-system.html

AwesomeMachine · 10-14-2018, 02:24 PM

I would use prime95 to stress test a cpu. It's available here: https://www.mersenne.org/download/

dd uses about 4% of the cpu.

shlomo.hovir · 10-14-2018, 02:44 PM

Quote:

Originally Posted by berndbausch

bs is block size, count is number of blocks. For example, with bs=1024k and count=100, dd will copy 100 1MB-blocks from input to output.

While I don't know what exactly you want to test, a simpler way of loading the CPU is to run a few yes coommands:

Code:

for i in {1..20}
do
    yes >/dev/null &
done

that doesn't heavy load my cpu
give another suggestion btw i dont want to use software that are used for benchmarking like cpuburn or prime95

shlomo.hovir · 10-14-2018, 03:03 PM

Quote:

Originally Posted by berndbausch

bs is block size, count is number of blocks. For example, with bs=1024k and count=100, dd will copy 100 1MB-blocks from input to output.

While I don't know what exactly you want to test, a simpler way of loading the CPU is to run a few yes coommands:

Code:

for i in {1..20}
do
    yes >/dev/null &
done

what does mean blocksize btw

scasey · 10-14-2018, 03:15 PM

Try

Code:

stress test cpu linux

in your favorite search engine. There are many, many links of advice.

berndbausch · 10-14-2018, 05:24 PM

Quote:

Originally Posted by shlomo.hovir

what does mean blocksize btw

A block is a chunk of data. Blocksize is the number of bytes in a block.

Quote:

that doesn’t heavy load my CPU

How do you measure your CPU load?

If 20 yes processes don’t load your CPU, launch 100 or 1000 processes. Or try dd as you originally planned.

AwesomeMachine · 10-14-2018, 08:54 PM

Quote:

Originally Posted by shlomo.hovir

btw i dont want to use software that are used for benchmarking like cpuburn or prime95

What actually is the object here? Maybe you could try 'stress-ng'?

Honest Abe · 10-14-2018, 11:42 PM

@OP,

You may also choose to run the dd command to copy to /dev/null (of=/dev/null). The source (if=) may be /dev/zero or /dev/random or /dev/urandom.
That way, nothing actually gets written (/dev/null is a 'blackhole'), and you may run multiple dd commands in parallel. (append '&' to the end of the command to run it in the background) to overcrowd you BUS IO operation and simulate a stress test.

Of course, this way you shall only be testing a small part of your resources, i.e. IO operation on a disk. For a comprehensive test, you should use a specific tool such as 'stress-ng'. This link should get you started.