I made these notes as a result of my experimentation with a Raspberry Pi. I kept messing up the software on the SD card and needed to start over, but it took a long time to go through all of the RPi setup steps. By copying the partitions, I was able to restore relatively quickly.
Get the info of each partition you want to copy on your SD card using diskutil:
$ diskutil info /dev/disk1s1
Device Identifier: disk1s1
Device Node: /dev/disk1s1
Part Of Whole: disk1
Device / Media Name: Untitled 1
Volume Name:
Escaped with Unicode:
Mounted: Yes
Mount Point: /Volumes/Untitled
Escaped with Unicode: /Volumes/Untitled
File System: MS-DOS FAT16
Type: msdos
Name: MS-DOS (FAT16)
Partition Type: Windows_FAT_32
...
$ diskutil info /dev/disk1s2
Device Identifier: disk1s2
Device Node: /dev/disk1s2
Part Of Whole: disk1
Device / Media Name: Untitled 2
Volume Name:
Escaped with Unicode:
Mounted: No
File System: fuse-ext2
Type: fuse-ext2
Name: fuse-ext2
Partition Type: Linux
...
This disk (/dev/disk1) has two partitions: an MS-DOS partition and a fuse-ext2 partition. We can back up each of these partitions using dd:
$ dd bs=1m if=/dev/rdisk1s1 of=backup-boot.img
$ dd bs=1m if=/dev/rdisk1s2 of=backup-root.img
You now have two partition images backup-boot.img and backup-root.img.
Restoring from backup
We’ve broken our SD card somehow and want to restore from backup.
Be sure to unmount (but not detach/eject) any existing filesystems on the SD card after inserting it. Now, you can partition the SD card using diskutil:
$ diskutil partitionDisk disk1 2 MBR MS-DOS "" 114688S fuse-ext2 "" 3665920S
Started partitioning on disk1
Unmounting disk
Creating partition map
Waiting for disks to reappear
Formatting disk1s1 as MS-DOS (FAT) with name
Formatting disk1s2 as fuse-ext2 with name
Finished partitioning on disk1
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: FDisk_partition_scheme *15.9 GB disk1
1: DOS_FAT_32 58.7 MB disk1s1
2: Linux 15.8 GB disk1s2
I’ve decided to create a 3rd “data” partition:
$ diskutil partitionDisk disk1 3 MBR MS-DOS boot 114688S fuse-ext2 root 3665920S fuse-ext2 data R
Started partitioning on disk1
Unmounting disk
Creating partition map
Waiting for disks to reappear
Formatting disk1s1 as MS-DOS (FAT) with name boot
Formatting disk1s2 as fuse-ext2 with name root
Formatting disk1s3 as fuse-ext2 with name data
[ 0%..10%..20%..30%..40%..50%..60%..70%..80%........... ]
Now we can restore our images to the SD card (be sure to unmount the partitions again after diskutil):
$ dd bs=1m if=backup-boot.img of=/dev/disk1s1
56+0 records in
56+0 records out
58720256 bytes transferred in 157.174893 secs (373598 bytes/sec)
When you write to the disk, use rdisk1sX instead of disk1sX. It copies data about 13x faster. I think this is because it is unbuffered (r for raw?)
Note: for the boot partition, don’t use the rdisk1s1—it doesn’t boot well.
Additional notes
Sat May 4 16:33:40 MDT 2013
As of today, here is the partition scheme I’m using:
$ diskutil partitionDisk disk1 5 MBR MS-DOS boot 114688S fuse-ext2 root 3665920S fuse-ext2 usr 6G fuse-ext2 home 8G fuse-ext2 backup R
Started partitioning on disk1
Unmounting disk
Creating partition map
Waiting for disks to reappear
Formatting disk1s1 as MS-DOS (FAT) with name
Formatting disk1s2 as fuse-ext2 with name root
Formatting disk1s3 as fuse-ext2 with name usr
Formatting disk1s5 as fuse-ext2 with name home
Formatting disk1s6 as fuse-ext2 with name backup
Finished partitioning on disk1
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: FDisk_partition_scheme *32.5 GB disk1
1: DOS_FAT_32 58.7 MB disk1s1
2: Linux root 1.9 GB disk1s2
3: Linux usr 6.0 GB disk1s3
4: Linux home 8.0 GB disk1s5
5: Linux backup 16.5 GB disk1s6
Last modified on 2013-04-28