Question

I’ll often create a file of a particular size with a trick like

dd if=/dev/zero of=1gb.dd bs=1M count=1024

or perhaps even

dd if=/dev/urandom of=1gb.dd bs=1M count=1024
dd if=/dev/random of=1gb.dd bs=1M count=1024

But what if I want to get all 1’s instead of 0’s or random?

Answer 1

For random data, in almost all cases use /dev/urandom. (You can also use /dev/random, but that’s much much slower because it’s entropy-bound. urandom is a PRNG which self-seeds from random.)

For a non-zero file, I’d suggest something like this:

perl -e 'print chr(0xff) x 1000' > t

Obviously, customise the 0xff and 1000 to taste.