[syslinux] help: booting dos from syslinux/memdisk

Christian Marg christian.marg at tu-clausthal.de
Thu Jul 3 00:09:57 PDT 2003

Hash: SHA1

Thomas Baumann wrote:
| Thanks for Remko for his help to solve the fractional cylinder problem.
| But there is the second problem, the boot disk failure (see below << [B])

I might have an explanation to that one too:
In your original Post you wrote:

| # creating a 16MB image with structure C/H/S 2/256/63
| mkdiskimage disk.img 2 256 63
| # creating dos filesystem
| mkdosfs disk.img

But you forgot that the image will be emulated as a Harddisk. DOS can't
boot from Harddisks without a partition table.
I don't know if mkdiskimage creates a part.table (no linux Box to test
it), but "mkdosfs disk.img" surely overwrites the Partition table if
there was one.

You should "cfdisk disk.img [...]" right after mkdiskimage. You have to
look up the parameters [...]to pass the geometry to it, since I did once
it but forgot how to...

After that you should use losetup (as root) to mount the diskimage with
a proper offset (which is usually the first track calculated in bytes,
in this case 63*512. You can look up the sector offset in cfdisk) to
point to the start of the partition. Then you can use mkdosfs on that
loop device.

Everything else you did should also be done using the loop device you

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