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My 2011 Mac Mini was running so slowly, that I decided to back up it’s entire hard disk, and switch to Ubuntu. For the backup process, I opted to boot into a live Ubuntu environment, then use dd to copy the entire hard drive to a USB external hard drive. I can’t remember the exact command, but it was something to the extent of–
dd if=/dev/sda | pv -petr > /media/ubuntu/usbhdd/apple-dapple-2016-sept-03.img
After ~5 hours, my new disk image was created on the USB HDD mounted at /media/ubuntu/usbhdd. Before deleting all the contents of the Mac Mini’s hard drive, I wanted to make sure the disk image was good, so I needed a way to mount the partitions that existed inside apple-dapple-2016-sept-03.img. I unmounted the USB HDD from the Mac Mini, and connected it to my laptop. On my laptop, as you’ll see below, the USB HDD was mounted to /media/chris/backup
Prerequisites
I’m not sure this is actually needed, but I’m putting it here just in case.
sudo apt-get -y install hfsplus
Mounting process
I started by making a mount point. This is where I mounted the filesystem to, so that I could browse to this directory and see all the files in the partition.
sudo mkdir -p /media/chris/mypartition
Next I needed to list the partitions on the dd image. fdisk won’t do, because fdisk doesn’t support GPT partition tables. Here I used parted. Setting the unit to B in parted was important, because the mount command expects offsets and sizes in bytes, not sectors.
sudo parted /media/chris/backup/grimmett-chris-mac-mini-2016-september-3-disk.img unit B print free
Model: (file)
Disk /media/chris/backup/apple-dapple-2016-sept-03.img: 500107862016B
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Number Start End Size File system Name Flags
17408B 20479B 3072B Free Space
1 20480B 209735679B 209715200B fat32 EFI System Partition boot
2 209735680B 471500587007B 471290851328B hfs+ Customer
4 471500587008B 484363347967B 12862760960B ext4
484363347968B 484363468799B 120832B Free Space
5 484363468800B 490959011839B 6595543040B ext4
6 490959011840B 499457720319B 8498708480B linux-swap(v1)
499457720320B 499457839103B 118784B Free Space
3 499457839104B 500107841535B 650002432B hfs+ Recovery HD
500107841536B 500107845119B 3584B Free Space
Using this output, I needed to find the start byte offset of the partition I wanted to mount, along with that partition’s total size. All my data was on the partition named, “Customer” and it starts at 209735680 (209735680B). Using that byte offset & byte partition size 471290851328, I was able to mount it.
sudo mount -t hfsplus -o loop,ro,offset=209735680,sizelimit=471290851328 /media/chris/backup/grimmett-chris-mac-mini-2016-september-3-disk.img /media/chris/mypartition
Now I was able to browse the files, and copy whatever I needed from the partition. It worked!
cd /media/chris/mypartition
ls
Applications cores dev home mach_kernel Network private System Users var
bin DamagedFiles etc Library net opt sbin tmp usr Volumes
This process took a lot of research. Lots of blogs and stackexchange answers instructed to specify a byte offset as an option for the mount command, but did not mention a sizelimit. I originally specified the byte offset, but not the sizelimit, so that resulted in an error–
mount: wrong fs type, bad option, bad superblock on /dev/loop2,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so
Following the instructions in the above error message, I saw these lines in the output of dmesg—
[ 9996.454670] hfsplus: invalid secondary volume header
[ 9996.454675] hfsplus: unable to find HFS+ superblock
And that’s what led me to the solution. This Superuser question about that same error.
HTH, GLHF HAGD
