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layout: post
title: Create a small disk image
date: 2008-01-23 22:26:52
updated: 2008-01-23 22:29:51
---
<div class="narrow-col">
<p>I needed a small disk image (a .dmg file) for the Lightroom <a href="/blog/lightroom-iphoto-export" title="Lightroom to iPhoto export">export plugin</a> I wrote earlier but for some reason the built-in &lsquo;Disk Utility&rsquo; program in Mac OS X Leopard does not allow you to create a disk image smaller than 10 <abbr title="megabyte">MB</abbr>. Sure, you can select a custom size but the tool changes it back to a minimum of 10 MB with the following message:</p>
<blockquote>The image size was changed to 10 MB because that is the minimum image size.</blockquote>
<p>I have no idea why it says that because you <strong>can</strong> make smaller disk images, just not via the Disk Utility program. Fire up &lsquo;Terminal&rsquo; and see for yourself. The following command creates a disk image in HFS+ format with a size of only 600 <abbr title="kilobyte">KB</abbr>:</p>
{% highlight bash %}
hdiutil create -size 600k myImage.dmg -srcfolder myFolder/ -fs HFS+
{% endhighlight %}
<p>The size can be specified with <samp>-size &lt; ?? | ??b | ??k | ??m | ??g | ??t | ??p | ??e &gt;</samp> but the minimum disk image size with this method is still 512 KB. I don't understand this minimum size as the created disk image is only as large as the data it contains. When I use this method to create a disk image with an empty folder the resulting image is only 10 KB, not 600 KB as specified in with the &lsquo;-size&rsquo; option.</p>
<h2>Other hdiutil uses</h2>
<ul>
<li>Use hdiutil to <a href="http://www.macosxhints.com/article.php?story=20040121135301830" title="Convert .dmg files to .iso files for burning elsewhere">convert .dmg files to .iso files</a> to burn them elsewhere.</li>
<li><a href="https://web.archive.org/web/20081108040341/http://www.commandlinemac.com:80/article.php/20071209133426668" title="Using hdiutil">Using hdiutil</a> for creating, (un)mounting, burning and encrypting disk images.</li>
</ul>
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