Not too tricky. Hopefully.
First of all, note the size and order of all your partitions on /dev/sda:
challenger:/home/michael # grep . /sys/block/sda/sda*/{start,size}
/sys/block/sda/sda1/start:63
/sys/block/sda/sda2/start:228690000
/sys/block/sda/sda3/start:257040
/sys/block/sda/sda1/size:256977
/sys/block/sda/sda2/size:83885760
/sys/block/sda/sda3/size:228432960
Run fdisk on /dev/sda and change the units to sectors:
Command (m for help): u
Changing display/entry units to sectors
Then start making partitions. Use the appropriate numbers start
and size
for each partition.
Avoid an off-by-one error - subtract one from size
before typing it into fdisk.
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First sector (63-312581807, default 63):
Using default value 63
Last sector, +sectors or +size{K,M,G} (63-312581807, default 312581807): +256976
Command (m for help): p
Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders, total 312581808 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x02b002af
Device Boot Start End Blocks Id System
/dev/sda1 63 257039 128488+ 83 Linux
Don't forget to set your partition IDs and toggle the boot flag on the right partition
Now re-install your MBR and you should be ready to go.
Naturally you can do all this using your favorite partition editor... parted works just fine as well.
If you've lost the information regarding start/end of partitions - parted has 'rescue' options to search the disk for lost partitions. But you shouldn't need those.
Best Answer
If you have a key that's simply hard-coded and always available to the system, then you're essentially defeating the entire point of having the disk encrypted in the first place. If you're set on that approach, create a LUKS key file and attach it into the crypttab for that device. See here for instructions.
A better option might be to have a TPM chip handle the key; it can provide secure storage for the encryption key and automatically provide it when needed. See this question for more info.