Create a random file on linux using dd and /dev/random

Question

I executed this:

$ dd if=/dev/random of=foo bs=1G count=1
0+1 records in
0+1 records out
6 bytes (6 B) copied, 0.00016958 s, 35.4 kB/s

$ stat -c "%s" foo
6

Also this does not work, I get stuck in the command:

$ head -c 500 /dev/random > foo

What is my mistake?

I'm on Linux mint.

Possible duplicate of Generate a random filename in unix shell — Alexander Guz
– Alexander Guz, Commented May 2, 2016 at 19:51
This question was not about the filename but the content. Not a duplicate. — Florian
– Florian, Commented May 3, 2016 at 1:42

Florian · Accepted Answer · 2016-05-02 19:40:25Z

5

/dev/random wil just deliver random data until the entropy sources for the RNG are exhausted. If you want to read bigger chunks of (pseudo-)random data, you can read from /dev/urandom instead.

answered May 2, 2016 at 19:40

Florian

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4 Comments

nowox Over a year ago

/dev/urandom is very very slow. It takes about 1minute to generate about 30MB. Is it normal?

nowox Over a year ago

Is it possible to generate bad random file quickly? I just wanna get a dummy file to benchmark a file transfer over nfs.

Florian Over a year ago

For that purpose, it should be sufficient to create a smaller file and concatenat that a couple of times to create a larger one: dd if=/dev/urandom bs=1024 count=1024 >1m; cat 1m 1m 1m 1m 1m >5m; cat 5m 5m 5m 5m 5m >25m; cat 25m 25m 25m 25m>100m

that other guy Over a year ago

That should indeed work for NFS. To generate test data for tools that are harder to fool like rsync or xz, you can use head -c 100m /dev/zero | openssl enc -aes-128-cbc -pass pass:"$(head -c 20 /dev/urandom | base64)" > my100MBfile.

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