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

Question

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.

Answer 1

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

something... | dd of=sample.txt bs=1G count=1 iflag=fullblock
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 iflag=fullblock

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 iflag=fullblock

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

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

Answer 2

Create a 1GB.bin random content file:

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

Answer 3

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.

Answer 4

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

Answer 5

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.

Answer 6

You could setup a bash-script for this like here. Get sure that you installed command 'pwgen' ... :

#!/bin/bash

touch cypher-01.txt

pwgen -sy 1024512 1024 >> cypher-01.txt

... this is finish and a file is created with randomly size of 1GB text. This takes on computer with 4 cores about ten minutes to fourteen minutes. To read this 1GB file with cat -A takes then about two and a half minutes.

Answer 7

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