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0 pointsape42mo ago0 comments

If I recall correctly:

    dd if=/dev/urandom of=/home/myrandomfile bs=1 count=N

0 comments

12 comments · 5 top-level

Twirrim2mo ago· 2 in thread

If you want to do it really quickly

    openssl enc -aes-256-ctr -pbkdf2 -pass pass:"$(date '+%s')" < /dev/zero | dd of=/home/myrandomfile bs=1M count=1024

Almost all CPUs have AES native instructions so you'll be able to produce pseudorandom junk really fast. Even my old system will produce it at about 3Gb/s. Much faster than urandom can go.

ape4OP2mo ago

That's very cool. Sadly running that exact command gets an incomplete file and error "error writing output file". It suggests adding iflag=fullblock (to dd). Running that makes a file of the correct size. But still gives "error writing output file". I suppose that occurs because dd breaks the pipe.

Twirrim2mo ago

Weird, I could have sworn that used to work, maybe I wrote the notes down wrong.

Easiest alternative I guess is to pipe through head. It still grumbles, but it does work

    openssl enc -aes-256-ctr -pbkdf2 -pass pass:"$(date '+%s')" < /dev/zero | head -c 10M > foo

dotancohen2mo ago· 2 in thread

My choice has always been `shred`:

  $ sudo truncate --size 1G /emergency-space
  $ sudo shred /emergency-space

I find it widely available, even in tiny distros.

ape4OP2mo ago

Very cool. Reading the man page I see, by default, shred does 3 iterations. Adding --iterations=1 makes it random enough for this purpose and faster.

dotancohen2mo ago

Terrific, thank you!

fragmede2mo ago· 2 in thread

bs=1 is a recipe for waiting far longer than you have to because of the overhead of the system calls. Better bs=N count=1

__david__2mo ago

That’s also not great if you’re trying to make a 10 gigabyte file. In that case, use bs=1M and count=SizeInMB.

marcosdumay2mo ago

Modern computers are crazily overengineered...

Most current desktops (smaller than your usual server) won't have any problem with the GP's command. Yours is still better, of course.

bugfix2mo ago· 1 in thread

I just use fallocate to create a 1GB or 2GB file, depending on the total storage size. It has saved me twice now. I had a nasty issue with a docker container log quickly filling up the 1GB space before I could even identify the problem, causing the shell to break down and commands to fail. After that, I started creating a 2GB file.

ape4OP2mo ago

Interesting! I did `fallocate -l 1G myfile` - very fast. Its all zeros but probably won't be compressed by the filesystem since its created with the fallocate() system call.

tdeck2mo ago

Fwiw you can also do this with

    head -c 1G /dev/urandom > /home/myrandomfile

And not have to remember dd's bizarre snowflake command syntax.

j / k navigate · click thread line to collapse

0 comments

12 comments · 5 top-level

Twirrim2mo ago· 2 in thread

If you want to do it really quickly

    openssl enc -aes-256-ctr -pbkdf2 -pass pass:"$(date '+%s')" < /dev/zero | dd of=/home/myrandomfile bs=1M count=1024

Almost all CPUs have AES native instructions so you'll be able to produce pseudorandom junk really fast. Even my old system will produce it at about 3Gb/s. Much faster than urandom can go.

ape4OP2mo ago

Twirrim2mo ago

Weird, I could have sworn that used to work, maybe I wrote the notes down wrong.

Easiest alternative I guess is to pipe through head. It still grumbles, but it does work

    openssl enc -aes-256-ctr -pbkdf2 -pass pass:"$(date '+%s')" < /dev/zero | head -c 10M > foo

dotancohen2mo ago· 2 in thread

My choice has always been `shred`:

  $ sudo truncate --size 1G /emergency-space
  $ sudo shred /emergency-space

I find it widely available, even in tiny distros.

ape4OP2mo ago

Very cool. Reading the man page I see, by default, shred does 3 iterations. Adding --iterations=1 makes it random enough for this purpose and faster.

dotancohen2mo ago

Terrific, thank you!

fragmede2mo ago· 2 in thread

bs=1 is a recipe for waiting far longer than you have to because of the overhead of the system calls. Better bs=N count=1

__david__2mo ago

That’s also not great if you’re trying to make a 10 gigabyte file. In that case, use bs=1M and count=SizeInMB.

marcosdumay2mo ago

Modern computers are crazily overengineered...

Most current desktops (smaller than your usual server) won't have any problem with the GP's command. Yours is still better, of course.

bugfix2mo ago· 1 in thread

ape4OP2mo ago

Interesting! I did `fallocate -l 1G myfile` - very fast. Its all zeros but probably won't be compressed by the filesystem since its created with the fallocate() system call.

tdeck2mo ago

Fwiw you can also do this with

    head -c 1G /dev/urandom > /home/myrandomfile

And not have to remember dd's bizarre snowflake command syntax.

j / k navigate · click thread line to collapse