Hi,
I was wondering how you could back up your MBR in case it is overwritten, for example. I know the command:

dd if=/dev/hda of=/root/mbr bs=512 count=1

but the shortcoming with this approach is that the partition table for only the primary partitions is saved. What would I do if I wanted the partition tables of the logical partitions to be saved. Would I do something like:

dd if=/dev/hda4 of=/root/mbrlogical bs=512 count=1

I'm asking because I'm not sure how big it should be or is. Is there any way to know? Thanks for your time.

If you are wanting to back up the partition table then I would use sfdisk:
sfdisk -d /dev/hda > part_layout.txt

Then you can restore with:
sfdisk /dev/hda < part_layout.txt

This is also a good way to set up partitions for a raid 1 system.

http://www.cpqlinux.com/ddbackup.html has an interesting discussion on this very topic.

Actually, that command works very nicely with extended / logical parttions also.

This will (probably) achieve what you are looking for.
IMHO a bit pointless, but that's o.k.
The "logical" part table(s) within each logical partition are chained (forward chain only). A single sector per logical partition should be sufficient.

Let's hope your root isn't mounted on the disk you are trying to salvage ...

Note that the MBR backup will also have the data for the extended partition in addition the the primary/primaries.

Edit: Go with sfdisk as suggested by david_ross.
*MUCH* better option - hadn't seen that use of it.

Thanks... So using sfdisk -d would dump both the MBR contents and the logical partition information in hdx4, right?

syg000, "Note that the MBR backup will also have the data for the extended partition in addition the the primary/primaries."

It should just have the data for the start and end of the extended partition but no information about the logical partitions.

Yep - all the partitions. Try it and have a look at the text file outputted.
This is true - I made no mention of logicals. That note was to alert you to the error of your first post;"but the shortcoming with this approach is that the partition table for only the primary partitions is saved".

Thanks for your help...