OS X dmg files – Disk Utility usually creates them read-only
Posted by jpluimers on 2017/11/27
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:
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
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