Sep 22

This post is very useful if you have ever needed to make a readonly mac .dmg file writable. Say for instance that you wanted to create a Mac OS X install disk, then mount it up writable, add something to it and then save it to be used to install OS X in say “VMware”. Listed below are the steps to make this happen:

From Terminal:
###This creates a writable dmg image###
hdiutil convert nameoffile.dmg -format UDRW -o nameoffile_writable.dmg

###This tells you the size of the image###
hdiutil resize -limits nameoffile_writable.dmg

###This resizes your dmg image so that you will have space to add stuff to it. Make sure you substitute the first number from the previous command and add to it sufficiently for the 9999etc. number###
hdiutil resize -sectors 999999 nameoffile_writable.dmg

###This mounts the new dmg writable image so that you can add stuff to it###
hdiutil attach nameoffile_writable.dmg


  1. Anonymous says:

    thank you!!!!!!

  2. Nate says:

    I’m not experienced (at all!) using terminal.

    But I’m trying to make a .dmg file writable. (I’m not even entirely sure how to confirm it’s not writable except that I’m not allowed to add any more docs to the disk.)

    Here is what I input into terminal, and the response I got back.

    nate-walters-computer:~ Nat$ hdiutil convert Tax docs.dmg -format UDRW -o Tax docs_writable.dmg
    hdiutil: convert: only a single input file can be specified
    Usage: hdiutil convert -format -o [options]
    hdiutil convert -help

    Can you help me figure out what I did wrong? Is it because I have a space in the disk name?

  3. crazyedy says:

    Yes, your problem is that you have a space in the disk name.

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