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Is My "SuperBlock" Corrupted?

Posted on 2013-10-29
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Last Modified: 2014-05-19
MacBook Pro 17-inch happily running Apple's most recent OS "Maverick" version 10.9 however that Mac had a recent history of superblock problems.

Is there any way I can determine whether my superblock is corrupted?

My Unix knowledge is next to nil, so be gentle.   ;-)

I use Apple's "Terminal" utility to type in Unix commands.

Tried to post a "comment" to expert "arnold" but I am a new member of EE so do not yet know how to navigate here.

arnold offered that Unix "fsck" should be used.

I entered a request for info' on how to use fsck by:  "man fsck" but the info' was apparently written is a combination of Latin and Greek.

I   _think_   that "fsck -b"   might be safe to use to force my Mac to use an alternate block of superblock data.

Then again it might blow up my Mac.  (again)


"man fsck" mutters something about an automatic reboot when using fsck.

I do not have the foggiest idea how that reboot will affect me if I use   fsck -b


SuperSenile -
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Question by:SuperSenile
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Eoin OSullivan earned 500 total points
ID: 39610933
@SuperSenile
Referring to your other Question which you marked as resolved would indicate that OSX is running OK following the reboot to the recovery partition and use of OSX Disk Utility recovery tools
http://www.experts-exchange.com/Apple/Operating_Systems/Q_28278486.html

In relation to your insecurity about the superblock data.  The superblock is a small bit of data that identifies the characteristics of your HD including size, format, block size etc.  As it is key to allow any OS to identify the nature of the HD it is replicated in multiple locations across the HD and not just a single copy.  This allows it to be recovered in the event of corruption.
Read a more detailed description of superblock here - http://www.linfo.org/superblock

Since you've run the OSX recovery process and your system now boots and runs properly there is NO indication that there is anything work with the superblock data on your HD now.

The OSX Disk Utility application is a visual front end to a number of UNIX tools including fsck so when you run Disk Utility in repair mode you're running fsck repair tools.

To be completely honest I see NO need to run the "fsck -b" command which is designed to replace the initial superblock with another from elsewhere on the HD.  Especially when you're not sure why you need to use it apart from a feeling of nervousness following the HD problems you had.

If you stay away from the Terminal and command line and simply use the Disk Utility application - verify disk command and repair permissions command these will address most issues on an OSX system now that the system is running properly.

Is there a reason you're not using Apple Time Machine or a 3rd party program like Carbon Copy Cloner to backup your Hard Drive to an external device?  These are stable, tried-and-tested on OSX and easy to configure and automate.
Using "dd" is not at all common on OSX as it is more commonly a Unix/Linux command and the OSX HFS filesystem is a little different from most other Linux flavours.
Read the manual for dd on OSX here
https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/dd.1.html
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by:SuperSenile
ID: 39613120
Thanks eoinosullivan, that is exactly the info' I needed.

There are several reasons I created the dd code:

1) Time Machine will not back up my Windows partition. (Boot Camp)

2) I want an exact mirror image backup of every block, even the "free space".

3) I just feel better with every possible part of the drive backed up.

For example in these sophisticated hacker days, with even our own NSA sticking their big fat noses in our private lives without our permission, I want to make it as difficult as possible for them to act like "Big Brother".

Its about freedom, do you want   _me_   running your life?    Of course not.

SuperSenile -
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