The Wiert Corner – irregular stream of stuff

While recovering the backups of a Retina MacBook Pro, I needed to know if I could mount a Disk Utility backup image on read-only mode.

Finding that info was a tad difficult as most results were about making dmg files read-write. This already hinted me in that most dmg files were readonly.

The main tool for handling dmg files is hdiutil. for which you can get more info here:

• [Archive.is] hdiutil(1) Mac OS X Manual Page
• [WayBack] Command Line Mac: Using hdiutil

The hdiutil command imageinfo will output a Format: line having the kind of dmg image:

• UDRW – UDIF read/write image
• UDRO – UDIF read-only image
• UDCO – UDIF ADC-compressed image
• UDZO – UDIF zlib-compressed image
• UDBZ – UDIF bzip2-compressed image (OS X 10.4+ only)
• UFBI – UDIF entire image with MD5 checksum
• UDRo – UDIF read-only (obsolete format)
• UDCo – UDIF compressed (obsolete format)
• UDTO – DVD/CD-R master for export
• UDxx – UDIF stub image
• UDSP – SPARSE (grows with content)
• UDSB – SPARSEBUNDLE (grows with content; bundle-backed)
• RdWr – NDIF read/write image (deprecated)
• Rdxx – NDIF read-only image (Disk Copy 6.3.3 format)
• ROCo – NDIF compressed image (deprecated)
• Rken – NDIF compressed (obsolete format)
• DC42 – Disk Copy 4.2 image

All compressed formats seem to be read-only and of course all read-only formats. Which then basically leaves only these as (potentialy) read-write image types:

• UDRW
• UFBI
• UDSP
• UDSB
• RdWr
• DC42

References and further reading:

• [WayBack] osx – Make DMG Readonly – Super User
• [WayBack] How to write to a Mac OSX read-only filesystem? – Super User
• [Archive.is] Best possible way to edit read only DMG | myjeeva blog
• [WayBack] DeMystifyinG the DMG file format
• [WayBack] Disk Image Formats – The iPhone Wiki
• [WayBack] Disk Utility’s hidden talents | Macworld
• [WayBack] Restoring from a disk image | Carbon Copy Cloner | Bombich Software
• I’m trying to do some research on TimeMachine right now. I don’t want to purchase an external hard drive, just to learn about some software, and so I’d like to be able to tinker with the settings, by

  [WayBack] time machine – How can I make my computer believe a disk image is a hardware disk? – Ask Different

–jeroen