It seems that in order to read the partition table an o/s must execute some executable code at the beginning of a disk, in the area known as the master boot record.

This bizarre design came into being so there is flexibility in the design of partitioning tables. It also means viruses can reside in the mbr, and that is where the first ever virus resided.

Nowadays mbr infections are rare, but I wonder. Does linux still execute the instructions in the mbr machine code to get a partition table?

This link will explain it better than I can:

http://en.wikipedia.org/wiki/Master_boot_record

1 members found this post helpful.

Before I read all of that, can we go straight to the answer? Is it "no" because that machine code is only executed when booting off that disk drive and not executed for other disk drives?

I might be mistaken, but doesn't the mbr run before the operating system?

The BIOS has no other way to pass control to operating system. It is done through MBR of disk selected as boot device in BIOS (I think in EFI this is different). For example there could be installed GRUB. And yes, the virus can reside there. It can be installed under running Linux (of course, it must bypass its security) or other system, so is not very secure to use the same drives with Linux and other OS, like Windows.

So a windows virus can execute in linux?

And the partition table of a data disk (ie not the one you boot) can be accessed without the mbr code being executed?

There are 3 possibilites:
1. You have installed 'wine' or similar software (not emulator) - if you explicty run Windows virus, it will run and can do anything that Linux user can do under that user account. The virus must known it is run under wine, to make changes in Linux filesystem. If not it will only can make changes in ~/.wine directory

2. I hear that virus can be compiled in a way to execute in both operating systems, but I don't known if it is true.

3. If virus in some way will change MBR it will run before any operating system, and can do anything.

Yes, code from MBR is only needed to start your operating system. To read partition layout there is no need to execute any code from MBR. Tools from operating system known how to read partition table.

No.

Syd00, surely you can come up with a "more than" 1 syllable answer.

I'm also intrigued by this issue.

But, have not had any trouble dual booting M$win on the same HD's as GNU/Linux.
(except lately, no boot sometimes).

Could I be wrong?

Please expand your answer.

Regards Glenn

<edit>I have good backups, restoring is an-other matter entirely. </edit>

As per #3, seems the OP isn't interested in putting any effort into finding out.
AFAIAC the following questions I also answered.

Nothing personal buddy (Syg00), just though you may have more to offer.

Glenn