long story short, i issued the following command:

dd if=/dev/zero of=/dev/sda bs=512 count=1

how do i recover my partitions and data?

you don't I'm afraid and afaik

well, i had no luck with gpart, testdisk, and fixdisktable. however, rescuept gave me some decent info. partitionmagic 8 gave me nothing. i can't believe the little 10 sec command took out the entire disk.


you see, i had a dual boot with winnt4 and redhat 7.3. i needed usb support so i thought this would be a great time to upgrade to win2k - takes too long in linux to get usb up and running. i did the upgrade but i had problems with grub. so i said why not wipe out grub. i tried the dos fdisk /mbr method but since my partition was 6gig ntfs, it would not work. so i looked for a linux way to wipe mbr. well the newsgroups gave me a great way! all i wanted was a way to use my usb2 sandisk drive so i could read some docs off it and get ahead in my job. i should have not gotten out of bed today.

That's the danger of trying stuff as root.
I feel your pain though, a long time ago I had something similar.
I sure hope nothing important was on that disk, always take backups.

If you had run lilo before doing that then in /boot there is a backup of the bootsector. I'm not sure what the number would be for sda but for hda it would be /boot.0300

The partition table is is between bytes 447 - 512 the first part would be lilo. If you do a dd if=/boot/boot.0300 of=/dev/hda then you will uninstall lilo. But thats easy to fix, just run lilo again.

You should be able to boot the Redhat into rescue mode and fix this.

jesus, you're right, it's only 512 bytes, totally looked over that.
Great

/dev/sda looks empty to the os. i ran gpart, rescuept , etc by moving the disk to another linux box since i would boot off the scsi disk. so would the scsi version of

dd if=/boot/boot.0300 of=/dev/hda

still work?

here is what i got from rescuept:

[root@localhost linux]# /sbin/rescuept /dev/sda
# partition table of /dev/sda
# total size 35566478 sectors
unit: sectors
# 0 MB candidate ext pt (type 5): sectors 1541061- 1541061
# 4001 MB found in ept (type 7): sectors 1541124- 9734210
# 4001 MB extended part ok (type 5): sectors 1541061- 9734210
# 10 MB small fat partition (type 1): sectors 10079654- 10100392
# 0 MB candidate ext pt (type 5): sectors 13109040- 13109040
# retracted
# 55 MB ext2 partition (type 83): sectors 13109040- 13221493
# 2000 MB fat partition (type 6): sectors 13221495- 17318069
# 0 MB candidate ext pt (type 5): sectors 17318070- 17318070
# 1004 MB found in ept (type 83): sectors 17318133- 19374389
# 3004 MB found in ept (type 83): sectors 19374453- 25527284
# 2000 MB found in ept (type 83): sectors 25527348- 29623859
# 133 MB found in ept (type 82): sectors 29623923- 29896964
# 1757 MB found in ept (type 6): sectors 29897028- 33495524
# 1004 MB found in ept (type 6): sectors 33495588- 35551844
# 8903 MB extended part ok (type 5): sectors 17318070- 35551844
/dev/sda0 : start= 1541061, size= 8193150, Id= 5
/dev/sda0 : start= 1541124, size= 8193087, Id= 7
/dev/sda0 : start= 10079654, size= 20739, Id= 1
/dev/sda0 : start= 13109040, size= 112454, Id=83
/dev/sda0 : start= 13221495, size= 4096575, Id= 6
/dev/sda0 : start= 17318070, size=18233775, Id= 5
/dev/sda0 : start= 17318133, size= 2056257, Id=83
/dev/sda0 : start= 19374453, size= 6152832, Id=83
/dev/sda0 : start= 25527348, size= 4096512, Id=83
/dev/sda0 : start= 29623923, size= 273042, Id=82
/dev/sda0 : start= 29897028, size= 3598497, Id= 6
/dev/sda0 : start= 33495588, size= 2056257, Id= 6



from what i can remember i had and the above output:

primary1: 6.4gb ntfs
primary2: 55mb ext3, /boot
primary3: ? not sure if i had a 3rd primary but the 2000 MB fat makes sense

extended:
1004 MB ext3, /
3004 MB ext3, /home
2000 MB ext3, /usr
133 MB swap
1757 MB fat
1004 MB fat

it is a 18.4 gb quantum atlas 10k iii scsi drive. I would really appreciate any tips or advice you can give me to restore the data.

Why don't you go ahead and try fdisk? The partition table is trashed the way it is, and if you mess up you know how to erase it right?

If you are having trouble converting the sectors into cylinders then just toggle fdisk to sectors using the u command.

ok, i got my data back! used fdisk -u and the output from rescuept to recreate the partition table. data has been backed up to another disk.

Great.

Even though lilo makes a backup of the bootsector I usually make another 1 or 5 backups and keep them on other partitions, or windows partitions or even floppy.

In your case you rebooted which made the drive unreadable. But if you had access to a backup bootsector you could have saved yourself alot of work.

For future reference, you could have undone the oops like this:
lilo -u # That would put the original bootsector (with the partition table) back on the drive.
lilo # This would reinstall lilo since the first command removed it.