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You are here: MacNN Forums > Software - Troubleshooting and Discussion > Mac OS X > Proper way to compress a .dmg file?

Proper way to compress a .dmg file?
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Jul 10, 2003, 12:02 AM
 
What's the proper way to compress a .dmg file?

We have a file available for download that end in .dmg.sit. The file downloads and mounts correctly in Safari and Mozilla/Netscape. However if you attempt to download the file in Internet Explorer under OS X, it tries to download it as a dmg file and cannot be mounted correctly. It launches Disc copy and gives "Error 95" rather than launching stuffit. This happens on any computer or user account we try.

Do I need to mount the image first, then run it through stuffit?

- If it matters the file is located at http://help.stargate.net/download/index.shtml

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Jul 10, 2003, 12:14 AM
 
Your best bet is to just create a compressed format disk image with Disk Copy. This eliminates the need to compress the image with another utility. In most cases Disk Copy can compress an image more efficiently than other formats such as .sit, .gz, etc.
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Jul 10, 2003, 07:08 AM
 
bzip2 gives decent compression on already-compressed disk images (sometimes 30-40%) but not much else does. Certainly not Stuffit.
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Jul 10, 2003, 11:08 AM
 
Originally posted by Art Vandelay:
Your best bet is to just create a compressed format disk image with Disk Copy. This eliminates the need to compress the image with another utility. In most cases Disk Copy can compress an image more efficiently than other formats such as .sit, .gz, etc.
The problem with this is that some servers don't have the MIME type set for dmg files, so when a user clicks a link to download the file, it just gets opened by the browser as a page of giberish (and they have to control/right click and select save link to disk, to force the download).
using dmg.sit overcomes this because all servers have set the type correctly for .sit files.
     
k3vmo  (op)
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Jul 10, 2003, 04:15 PM
 
That was part of the problem. The .dmg file by itself just displayed binary code in Netscape/Mozilla and Safari. Oddly the .dmg file worked in Internet Explorer, but I need some way for it to work correctly.
     
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Jul 11, 2003, 01:29 AM
 
Just set up your webserver to serve .dmg files as MIME type "application/object-stream", or ask your sysadmin to. It's a lot better than filling people's desktops up with the intermediary stages of decompressing a .dmg.sit.tgz.hqx file as some developers are wont to do.

If you compress your disk image using the command-line hdiutil tool, you can get the best size by using level-9 zlib compression -- after that, even bzip2 will only save you a percent or two. To do that:
Code:
% hdiutil convert MyOriginalDiskImage.dmg -format UDZO -imagekey zlib-level=9 -o MyCompresedDiskImage
Rick Roe
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