Something really dumb happened to me recently: I was playing doctor with my Galaxy Nexus when a got hung up in a dreaded bootstrap. Luckily I had laid out a backup beforehand, which was something I absolutely didn't want have to restore. So what should I do?
Backups are the meat and potatoes of root experimentations. Before you make even the smallest change to your system, you should first create a backup in the recovery with Nandroid. This way you are always on the safer side of things...or so I thought yesterday at any rate.
Last night when I wanted to load my previously laid out backup, I only got the following message: ''MD5 mismatch!''. This means that the backup's determined checksum was not attune with the expected checksum. In that moment, I was up a creek without a paddle. An incorrect MD5 checksum suggests modified or corrupted data. In this case, it can also mean that there is a problem with Nandroid, in which none of my backups can be restored. Obviously I could've simply conducted a full wipe, but I didn't want to lose my data and then have to piece the puzzle back together again. So I took it upon myself to find a solution and after many flops, I struck it rich.
I found the saving command in the XDA-Developers forum. All that I need for this is a development environment with ADB. From there, you open a command line and enter the following order:
# cd /sdcard/clockworkmod/backup/<Name Eures Backups>
# rm nandroid.md5
# md5sum *img > nandroid.md5
Using these commands, you first delete the MD5 data that already exists, which contains the checksum and then subsequently create a new MD5 checksum, that you will eventually save in a file. After this you can restore the backup.
Important: Only because this worked for me does it nowhere near mean that it will also work for you. In the worst case, your backup will be damaged and after the recovery, you will only obtain errors and crashes. Thankfully it worked for me and my Galaxy Nexus was afterwards operational again.
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(Photo: Nico Heister/AndroitPIT)