CODEWITHSUNDEEP
linuxunixcommand
Saja Peiris
Saja Peiris

Reputation: 9

How to run multiple instances of this command dd

I want to run this command multiple times but im not sure how to do it. It has to be a single command. what this command does is it pushes my cpu cores to %100 

dd if=/dev/zero of=/dev/null

Its for an assignment. please help if you can thank you

This is what in the assignment says. Maybe it can be helpfull to figure it out

"Figure out how to run multiple instances of the command dd if=/dev/zero of=/dev/null at the same time. You could also use the command sum /dev/zero. You should run one instance per CPU core, so as to push CPU utilization to 100% on all of the CPU cores in your virtual machine. You should be able to launch all of the instances by running a single command or pipeline as a regular user "

so far i tried doing 

dd if=/dev/zero of=/dev/null | xargs -p2

but that doesn't do the job right

Upvotes: 0

Views: 5259

Answers (4)

user10277898
user10277898

Reputation:

Or you could try my home made parallel data transfer tool pdd. This tool spawns several threads and each of the threads is bond to a CPU core.

Upvotes: 0

Ole Tange
Ole Tange

Reputation: 33748

This will run 4 copies:

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

But it is really not recommended as a solution for homework, as it looks as if you do not understand what | does. Here nothing is being sent through the pipe. It has the advantage that it is easy to stop with a Ctrl-C.

If the goal is simply to increase carbon emissions then this is shorter:

 burnP6 | burnP6 | burnP6 | burnP6

If you have GNU Parallel:

yes /dev/zero | parallel dd if={} of=/dev/null
yes | parallel burnP6

GNU Parallel starts by default 1 job per CPU core, and thus it only reads that many arguments from yes.

Upvotes: 1

alvits
alvits

Reputation: 6768

Your assignment is probably already due and over. But for future readers, here's a single line solution.

perl -e 'print "/dev/zero\n" x'$(nproc --all) | xargs -n 1 -P $(nproc --all) -I{} dd if={} of=/dev/null

How does this work? Let's dissect the pipeline.

nproc --all will return the number of cores in the system. Let's pretend your system has 4 cores.

perl -e 'print "/dev/zero\n" x 4' will print 4 lines of /dev/zero.

Output

/dev/zero
/dev/zero
/dev/zero
/dev/zero

The output of perl is then passed to xargs.

-n 1 tells xargs to use only one argument at a time.

-I {} tells xargs that the argument shall replace the occurrences of {}

-P 4 tells xargs to run as many as 4 instances of the command in parallel

A shorter version of the above command can be written like this:

perl -e 'print "if=/dev/zero of=/dev/null\n" x '$(nproc --all) | xargs -n2 -P0 dd

Upvotes: 1

zsram
zsram

Reputation: 386

Many ways.. for example repeating the command four times:

command & ; command & ; command & ; command &

..or in a more systematic way:

for i in {1..4}
do
   dd if=/dev/zero of=/dev/null &
done

Upvotes: 0

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