bup-random(1) Bup 0.33.3

Avery Pennarun



bup-random - generate a stream of random output


bup random [-S seed] [-fv] <numbytes>


bup random produces a stream of pseudorandom output bytes to stdout. Note: the bytes are not generated using a cryptographic algorithm and should never be used for security.

Note that the stream of random bytes will be identical every time bup random is run, unless you provide a different seed value. This is intentional: the purpose of this program is to be able to run repeatable tests on large amounts of data, so we want identical data every time.

bup random generates about 240 megabytes per second on a modern test system (Intel Core2), which is faster than you could achieve by reading data from most disks. Thus, it can be helpful when running microbenchmarks.


the number of bytes of data to generate. Can be used with the suffices k, M, or G to indicate kilobytes, megabytes, or gigabytes, respectively.
-S, --seed=seed
use the given value to seed the pseudorandom number generator. The generated output stream will be identical for every stream seeded with the same value. The default seed is 1. A seed value of 0 is equivalent to 1.
-f, --force
generate output even if stdout is a tty. (Generating random data to a tty is generally considered ill-advised, but you can do if you really want.)
-v, --verbose
print a progress message showing the number of bytes that has been output so far.


$ bup random 1k | sha1sum
2108c55d0a2687c8dacf9192677c58437a55db71  -

$ bup random -S1 1k | sha1sum
2108c55d0a2687c8dacf9192677c58437a55db71  -

$ bup random -S2 1k | sha1sum
f71acb90e135d98dad7efc136e8d2cc30573e71a  -

$ time bup random 1G >/dev/null
Random: 1024 Mbytes, done.

real   0m4.261s
user   0m4.048s
sys    0m0.172s

$ bup random 1G | bup split -t --bench
Random: 1024 Mbytes, done.
bup: 1048576.00kbytes in 18.59 secs = 56417.78 kbytes/sec


Part of the bup(1) suite.