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><A
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></A
>8. Recovering a Deleted Partition Table</H1
><P
> Below are instructions for manually recovering a deleted partition
table. There are utilities such as <A
HREF="http://www.stud.uni-hannover.de/user/76201/gpart"
TARGET="_top"
>gpart</A
>
or <A
HREF="http://www.cgsecurity.org/index.html?testdisk.html"
TARGET="_top"
>TestDisk
</A
> which can make this task considerably easier. If you are
reading this, however, because you have run out of luck, this is
what you will have to do:
</P
><P
>
<P
></P
><OL
TYPE="1"
><LI
><P
>Make a partition that is at least as big as your first partition
was. You can make it larger than the original partition by any
amount. If you underestimate, there will be much wailing and
gnashing of teeth.
<TABLE
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WIDTH="100%"
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><TD
><FONT
COLOR="#000000"
><PRE
CLASS="programlisting"
> Command (m for help): <TT
CLASS="userinput"
><B
>n</B
></TT
>
Command action
e extended
p primary partition (1-4)
<TT
CLASS="userinput"
><B
>p</B
></TT
>
Partition number (1-4): <TT
CLASS="userinput"
><B
>1</B
></TT
>
First cylinder (1-23361, default 1): <TT
CLASS="userinput"
><B
><RETURN></B
></TT
>
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-22800, default 22800): <TT
CLASS="userinput"
><B
>13032</B
></TT
>
Command (m for help): <TT
CLASS="userinput"
><B
>w</B
></TT
>
</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></LI
><LI
><P
> Run <B
CLASS="command"
>dumpe2fs</B
> on the first partition and grep out the block count.
</P
><P
> Example:
<TABLE
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><TD
><FONT
COLOR="#000000"
><PRE
CLASS="programlisting"
> % dumpe2fs /dev/sda1 | grep "Block count:"
Block count: 41270953
</PRE
></FONT
></TD
></TR
></TABLE
>
If you are uncertain about this value, repeat Step 1 with a
bigger partition size. If the block count changes, then you
underestimated the size of the original partition. Repeat Step
1 until you get a stable block count.
</P
></LI
><LI
><P
> Remove the partition you just created
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><TD
><FONT
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><PRE
CLASS="programlisting"
> Command (m for help): <TT
CLASS="userinput"
><B
>d</B
></TT
>
Partition number (1-4): <TT
CLASS="userinput"
><B
>1</B
></TT
>
</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></LI
><LI
><A
NAME="BlockSize"
></A
><P
>Make a new partition with the exact size you got from the block
count. Since you cannot enter block size in fdisk, you need to
figure out how many cylinders to request. Here is the formula:
</P
><P
> <TABLE
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><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="programlisting"
> (number of needed cylinders) = (number of blocks) / (block size)
(block size) = (unit size) / 1024
(unit size) = (number of heads) * (number of sectors/cylinder) * (number of bytes/sector)
</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
> Consider the following example, where a hard drive has been partitioned into four primary
partitions of 1, 2, 4, and 8 cylinders.
<TABLE
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><TD
><FONT
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><PRE
CLASS="programlisting"
> disk /dev/sda: 16 heads, 63 sectors, 23361 cylinders
Units = cylinders of 1008 * 512 bytes
Device Boot Start End Blocks Id System
/dev/sda1 1 2 976+ 83 Linux
/dev/sda2 3 5 1512 83 Linux
/dev/sda3 6 10 2520 83 Linux
/dev/sda4 11 19 4536 83 Linux
</PRE
></FONT
></TD
></TR
></TABLE
>
<B
CLASS="command"
>fdisk</B
> provides the configuration information I need in the head of the output.
The unit size is <TT
CLASS="userinput"
><B
>516096</B
></TT
> ( <TT
CLASS="userinput"
><B
>16</B
></TT
> heads * <TT
CLASS="userinput"
><B
>63</B
></TT
> sectors/cyl * <TT
CLASS="userinput"
><B
>512</B
></TT
> bytes/sector ).
The block size is <TT
CLASS="userinput"
><B
>504</B
></TT
> ( <TT
CLASS="userinput"
><B
>516096 / 1024</B
></TT
> ).
The number of needed cylinders for the second partition is therefore <TT
CLASS="userinput"
><B
>3</B
></TT
> ( <TT
CLASS="userinput"
><B
>1512</B
></TT
> blocks <TT
CLASS="userinput"
><B
>/
504</B
></TT
> ).
The partition table shows that this is indeed the case: the first cylinder is <TT
CLASS="userinput"
><B
>3</B
></TT
>, the second <TT
CLASS="userinput"
><B
>4</B
></TT
>, and
the last is <TT
CLASS="userinput"
><B
>5</B
></TT
>, for a total of three cylinders.
The number of needed cylinders for the third partition is calculated similarly: <TT
CLASS="userinput"
><B
>2520</B
></TT
> blocks
<TT
CLASS="userinput"
><B
>/ 504 = 5</B
></TT
>, which corresponds to blocks <TT
CLASS="userinput"
><B
>6,7,8,9,10</B
></TT
>
.
Notice that this calculation does not work for the first partition because the block count is
wrong ( <TT
CLASS="userinput"
><B
>976</B
></TT
> instead of <TT
CLASS="userinput"
><B
>1008</B
></TT
> ). The plus sign indicates that not all the blocks are included in
the fdisk value. When you try the calculation ( <TT
CLASS="userinput"
><B
>976 / 504</B
></TT
> ) you get <TT
CLASS="userinput"
><B
>1.937</B
></TT
>. Knowing that
the number of cylinders must be an integer, you can simply round up.
</P
></LI
><LI
><P
>Run <B
CLASS="command"
>e2fsck</B
> on it to verify that you can read the new partition.
</P
></LI
><LI
><P
> Repeat Steps 1-5 on remaining partitions.
</P
></LI
></OL
>
Remount your partitions. Amazingly, all of your data will be there.
</P
><P
> Credit goes to: Mike Vevea, jedi sys admin, for providing the basic strategy.
</P
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