Subject: Ideas on one-floppy installation
To: None <>
From: Gordon W. Ross <>
List: current-users
Date: 10/19/1994 00:21:06
> Reply-To:
> X-Reposting-Policy: redistribute only with permission
> Date: Tue, 18 Oct 1994 10:42:11 -0400
> From: "Perry E. Metzger" <>
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> Precedence: list

> I don't think, however, that the "memory filesystem" approach to
> booting is impossible. Here is an idea.


> You then need a way to use the memory you've just saved as a disk -- I
> suggest an astonishingly simple minded driver built into into the
> initial kernel that uses the top couple of meg as a ram disk.  Given a
> kernel that "knows" not to know about the top of memory and a driver
> that can read that memory as disk, the proceedure becomes this...
> 1) the hacked boot loads the hacked kernel into memory, and prompts
>    you to change floppies.
> 2) The hacked boot loads the second floppy verbatim (sector for
>    sector) into the top of memory.
> 3) The hacked boot starts the kernel which you tell that root is on
>    the "in memory" file system.
> You now no longer have any dependancy at all on the floppy drive.
> This seems straightforward to do, but also seems like a bunch of work.
> It would be rather cool, of course...
> Perry

Here is the typical RAM-disk root approach:  (SunOS, some SysV)

(1) Kernel is configured to use RAM-disk ("rd") as root device
(2) The "rd" init routine stops the world as if in kernel debug
    and reads in a RAM-disk image from some predetermined place.
	(typically it prompts: "insert boot diskette 2")
(3) The mountroot call proceeds on the open block device with the
    file system image copied in by the open call.

This is quite easy to do...