Comments on: How to create a large empty file in osx?

Question: How to create a large empty file in osx?

greggish — Sat, 16 Aug 2008 06:16:54 -0800

How do I create a very large (+10gb) empty file in OSX?

I've found some instructions on doing this through disk partitioning, but the external hard drive i have accessible right now has stuff on it - and i don't want to accidentally erase it all... i just want a large file full of zeroes.

By: claudius

claudius — Sat, 16 Aug 2008 06:22:54 -0800

Open the terminal and type
dd if=/dev/zero of=<filename> bs=1024 count=10485760

I believe that os x has dd installed, and had as a /dev/zero.

By: claudius

claudius — Sat, 16 Aug 2008 06:23:39 -0800

Er... has a /dev/zero

By: Popular Ethics

Popular Ethics — Sat, 16 Aug 2008 10:26:28 -0800

Alternatively, open Disk Utility, press "New Image", change the "Volume Size" to 10Gb, and save the resulting blank *.dmg file wherever you like.

By: Popular Ethics

Popular Ethics — Sat, 16 Aug 2008 10:32:19 -0800

How important is it that the whole file be zeros? A dmg is going to have some file system header stuff, even if the rest of the file is blank.

By: greggish

greggish — Sat, 16 Aug 2008 10:39:10 -0800

hrm, i was getting a "No such file or directory" in the terminal, and in the disk utility it wouldn't let me create the "New Image" (and didn't even give me the option of "Volume Size"), instead told me that the resource was busy. am i doing something wrong?

By: bottlebrushtree

bottlebrushtree — Sat, 16 Aug 2008 10:45:11 -0800

For those that these commands are arcane, I've also taken a large file that you would care that people saw the data from (a big picture or movie or application) and then copied it over and open again, stopping every once and a while to select more of the copies with "select all" until I fill up the disk. It's not as secure as dd or dedicated applications, but works in a pinch.

By: sergeant sandwich

sergeant sandwich — Sat, 16 Aug 2008 10:54:22 -0800

i just tested claudius's thing (with a smaller count) and it works under OSX, but for some reason you have to specify the full path in "of=filename" part. specifying the path with ~ was giving me the same "No such file or directory" error, which i don't understand.

so putting of=/Users/greggish/Desktop/zeros.txt there will put the file on your desktop, for example.

By: fantabulous timewaster

fantabulous timewaster — Sat, 16 Aug 2008 12:07:49 -0800

~ is expanded by the shell, not by the program called, and only at the beginning of a token:

$ echo ~/foo; echo foo/~; echo of=~foo /Users/rob/foo foo/~ of=~foo

This lets you use ~ in filenames.

By: chairface

chairface — Sat, 16 Aug 2008 20:08:17 -0800

If you just want to fill up the disk, dd is unnecessary. Good ol' cp will work file:

$ cp /dev/zero /path/to/big/file

I do this myself before disposing of old disks.

By: chairface

chairface — Sat, 16 Aug 2008 20:08:36 -0800

Bah file=>fine

By: zouhair

zouhair — Sun, 17 Aug 2008 11:01:34 -0800

chairface: "If you just want to fill up the disk, dd is unnecessary. Good ol' cp will work file:

$ cp /dev/zero /path/to/big/file

I do this myself before disposing of old disks."

dd is much better, you can set the size of the file.

By: majick

majick — Mon, 18 Aug 2008 19:03:18 -0800

Actually, it's much easier just to use mkfile this way:

$ mkfile 10g /path/to/my/tengigfile

If you want it created sparsely, use the -n parameter.