Last updated on September 19, 2021
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
I’m not sure this is actually needed, but I’m putting it here just in case.
sudo apt-get -y install hfsplus
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
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
[ 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
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