How do I create a 1GB random file in Linux?

I am using the bash shell and would like to pipe the out of the command openssl rand -base64 1000 to the command dd such as dd if={output of openssl} of="sample.txt bs=1G count=1. I think I can use variables but I am however unsure how best to do so. The reason I would like to create the file is because I would like a 1GB file with random text.

1

6 Answers

if= is not required, you can pipe something into dd instead:

something... | dd of=sample.txt bs=1G count=1
something... | head -c 1G > sample.txt

It wouldn't be useful here since openssl rand requires specifying the number of bytes anyway. So you don't actually need dd – this would work:

openssl rand -out sample.txt -base64 $(( 2**30 * 3/4 ))

1 gigabyte is usually 2³⁰ bytes (though you can use 10**9 for 10⁹ bytes instead). The * 3/4 part accounts for Base64 overhead, making the encoded output 1 GB.

Alternatively, you could use /dev/urandom, but it would be a little slower than OpenSSL:

dd if=/dev/urandom of=sample.txt bs=1G count=1

I would use bs=64M count=16 or similar, so that 'dd' won't try to use the entire 1 GB of RAM at once:

dd if=/dev/urandom of=sample.txt bs=64M count=16

or even the simpler head tool – you don't really need dd here:

head -c 1G /dev/urandom > sample.txt

15

Create a 1GB.bin random content file:

 dd if=/dev/urandom of=1GB.bin bs=64M count=16 iflag=fullblock

1

Since, your goal is to create a 1GB file with random content, you could also use yes command instead of dd:

yes [text or string] | head -c [size of file] > [name of file]

Sample usage:

yes this is test file | head -c 100KB > test.file

If you want EXACTLY 1GB, then you can use the following:

openssl rand -out $testfile -base64 792917038; truncate -s-1 $testfile

The openssl command makes a file exactly 1 byte too big. The truncate command trims that byte off.

1

If you just need a somewhat random file which is not used for security related things, like benchmarking something, then the following will be significantly faster:

truncate --size 1G foo
shred --iterations 1 foo

It's also more convenient because you can simply specify the size directly.

Try this script.

#!/bin/bash
openssl rand -base64 1000 | dd of=sample.txt bs=1G count=1

This script might work as long as you don't mind using /dev/random.

#!/bin/bash
dd if=/dev/random of="sample.txt bs=1G count=1"

6

Your Answer

Sign up or log in

Sign up using Google Sign up using Facebook Sign up using Email and Password Submit

Post as a guest

Post Your Answer Discard

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy