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Top Forums Shell Programming and Scripting Enhanced partition copy script (new & improved!) Post 302448738 by jwzumwalt on Friday 27th of August 2010 12:00:50 AM
Old 08-27-2010
I'm not sure I understand what you are asking but here is a bit of additional information that may or may not answer your question.

The partition information for an entire drive is kept in the MBR (master boot record). There is no separate or individual information block available. Therefore my program (and any other) that attempts to save the first 512 bytes of a partition (which is the mbr) for any partition other than the first will receive an error.

My program does not attempt to stop someone from saving an invalid MBR block on other partitions. dd is smart enough to notice that an attempt is being made to save the MBR of an invalid partition and will shoot out an error message, but it still saves the invalid 512 byte block.

This first example will work because the mbr is actualy at the start of partition 1
Code:
dd if=hda1 of=partition.mbr.img count=1 bs=512

This example will cause an error message because the 2nd partition does not have an mbr!
Code:
dd if=hda2 of=partition.mbr.img count=1 bs=512

My thinking is that there may be some special case that I am not aware of that a user may need that 512 byte block. So, I trust the users judgment.

In the future, I will place some type of error trap and give sa message to the user that explains what is going on.

I hope this information helps.

Jan Zumwalt
 

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HD(4)							     Linux Programmer's Manual							     HD(4)

NAME
hd - MFM/IDE hard disk devices DESCRIPTION
The hd* devices are block devices to access MFM/IDE hard disk drives in raw mode. The master drive on the primary IDE controller (major device number 3) is hda; the slave drive is hdb. The master drive of the second controller (major device number 22) is hdc and the slave hdd. General IDE block device names have the form hdX, or hdXP, where X is a letter denoting the physical drive, and P is a number denoting the partition on that physical drive. The first form, hdX, is used to address the whole drive. Partition numbers are assigned in the order the partitions are discovered, and only non-empty, non-extended partitions get a number. However, partition numbers 1-4 are given to the four partitions described in the MBR (the `primary' partitions), regardless of whether they are unused or extended. Thus, the first logi- cal partition will be hdX5. Both DOS-type partitioning and BSD-disklabel partitioning are supported. You can have at most 63 partitions on an IDE disk. For example, /dev/hda refers to all of the first IDE drive in the system; and /dev/hdb3 refers to the third DOS `primary' partition on the second one. They are typically created by: mknod -m 660 /dev/hda b 3 0 mknod -m 660 /dev/hda1 b 3 1 mknod -m 660 /dev/hda2 b 3 2 ... mknod -m 660 /dev/hda8 b 3 8 mknod -m 660 /dev/hdb b 3 64 mknod -m 660 /dev/hdb1 b 3 65 mknod -m 660 /dev/hdb2 b 3 66 ... mknod -m 660 /dev/hdb8 b 3 72 chown root:disk /dev/hd* FILES
/dev/hd* SEE ALSO
mknod(1), chown(1), mount(8), sd(4) Linux 1992-12-17 HD(4)
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