Hi,
I made disk images with all my projects made in the 1990s and early 2000s. I've stored them on multiple drives, and the files used to open. I think the last time I opened them was in 2014. None of them will open. I dont have an older Mac to try opening them on, mine are using the latest os and from 2016 and 2020. Any advise on what to do, or are these lost forever. The error message I get is "no mountable file systems".
The DMG file may be damaged or it may just be so incredibly old and the latest macOS Big Sur no longer supports the older file format. It may contain multiple partitions, resource forks, etc. This was prior to HFS being journaled, etc. This also predates sparse disk images.
However, all is not lost. First of all make a copy of the DMG image file on the newer Big Sur Mac. You might be able to use Unix commands to find out more information and possibly work around the problem. But the built-in Disk Utility may be worthless with very old DMG files.
Open Terminal and attempt this command to write out the debug information of the DMG file.
hdid /Users/<YourHomeFolder>/<PathToFileLocation>/<filename>.dmg -nomount -verbose -debug > disk_debug.txt
The above will scan the file and output all the debugging details about the file to a disk_debug.txt file.
Please reply and attach disk_debug.txt file contents. It may provide insight to the root cause problem.
You might be able to use a similar command to list the unmounted disk and then use the 'dd' command to disk duplicate it to a new physical external disk.
diskutil list
Determine which disk it is, example /dev/disk3, etc. Also determine which disk your external physical drive is.
WARNING! THE dd COMMAND WILL OVERWRITE ANYTHING ON THE "of=/dev/disk5/" BE ABSOLUTELY SURE YOU HAVE THE CORRECT DEVICE OBTAINED FROM THE DISKUTIL LISTING. THIS IS SOMEWHAT DANGEROUS IF YOU SPECIFY THE WRONG DISK YOU WILL LOSE DATA OR IF Y
dd if=/dev/disk3 of=/dev/disk5 bs=131072
Where /dev/disk3 is the DMG image and /dev/disk5 is an external physical drive with nothing you care about on it. The 'bs' is the block size buffer which could be more accurately calculated to give enough buffer room to speed up the process as much as 20 times. However, the value of 131072 should be sufficiently large enough to make a difference in most any modern scenario. If it's taking a ridiculously long amount of time you could abort with Ctrl+C and try again with a 'bs=8M' which gives it considerably more elbow room.
If this works and you manage to be able to access your data files on the external disk, back them up. Then rinse and repeat for any other DMG disk images you may be.
Alternative methods:
The DMG file may be damaged or it may just be so incredibly old and the latest macOS Big Sur no longer supports the older file format. It may contain multiple partitions, resource forks, etc. This was prior to HFS being journaled, etc. This also predates sparse disk images.
However, all is not lost. First of all make a copy of the DMG image file on the newer Big Sur Mac. You might be able to use Unix commands to find out more information and possibly work around the problem. But the built-in Disk Utility may be worthless with very old DMG files.
Open Terminal and attempt this command to write out the debug information of the DMG file.
hdid /Users/<YourHomeFolder>/<PathToFileLocation>/<filename>.dmg -nomount -verbose -debug > disk_debug.txt
The above will scan the file and output all the debugging details about the file to a disk_debug.txt file.
Please reply and attach disk_debug.txt file contents. It may provide insight to the root cause problem.
You might be able to use a similar command to list the unmounted disk and then use the 'dd' command to disk duplicate it to a new physical external disk.
diskutil list
Determine which disk it is, example /dev/disk3, etc. Also determine which disk your external physical drive is.
WARNING! THE dd COMMAND WILL OVERWRITE ANYTHING ON THE "of=/dev/disk5/" BE ABSOLUTELY SURE YOU HAVE THE CORRECT DEVICE OBTAINED FROM THE DISKUTIL LISTING. THIS IS SOMEWHAT DANGEROUS IF YOU SPECIFY THE WRONG DISK YOU WILL LOSE DATA OR IF Y
dd if=/dev/disk3 of=/dev/disk5 bs=131072
Where /dev/disk3 is the DMG image and /dev/disk5 is an external physical drive with nothing you care about on it. The 'bs' is the block size buffer which could be more accurately calculated to give enough buffer room to speed up the process as much as 20 times. However, the value of 131072 should be sufficiently large enough to make a difference in most any modern scenario. If it's taking a ridiculously long amount of time you could abort with Ctrl+C and try again with a 'bs=8M' which gives it considerably more elbow room.
If this works and you manage to be able to access your data files on the external disk, back them up. Then rinse and repeat for any other DMG disk images you may be.
Alternative methods:
Those old images are using an older no longer supported partitioning/file system (APM ?). You can try installing an older version of macOS into a Virtual Machine to see if they can be opened if you don't have access to another older working Mac.
You can probably use Linux to open those old .dmg archives although they may need to be uncompressed first into a standard raw image (.img) file before they can be opened which can be done using special Linux utilities.
How are the drives formatted that are storing the dmg files? If it's not either OS X Extended (journaled) or APFS the copy a dmg file to your Desktop and try opening it from there.
Otherwise, boot into Safe Mode according to Start up your Mac in safe mode - Apple Support , copy the dmg file to your Desktop and try mounting them from there. If success create a new dmg file and save back to an EHD that's formatted either APFS or OS X Extended (journaled). When done reboot normally.
NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following;
• Verifies your startup disk and attempts to repair directory issues, if needed
• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts
• Deletes font caches, kernel cache, and other system cache files
Disk images made between 1997 and 2002 wont mount
