[Qemu-devel] Re: No useful documentation.

[Emmanuel Charpentier <charpent@bacbuc.dyndns.org>]

Dear Daniel,

Daniel Carrera a écrit :
> Hello,
> 
> I write here because there doesn't seem to be a Bugzilla for qemu and
> whoever is responsible for the qemu documentation must be here.
> 
> The documentation is quite worthless.

I cannot agree. Qemu doc is (more or less) adequate *for people already 
familiar with coping with bare hardware*. Read along

> I'm sure you don't like hearing that, but consider that it doesn't
> actually show the user how get qemu to do what qemu is supposed to di
> (ie. run a host OS). Ok, it tells me how to create a blank disk image,
> that's great, but how do I create a disk image with something bootable
> on it? Sorry, no information on that. I expect that the most typical use
> case for qemu is running Windows under Linux, so you'd expect to see
> some documentation for that, right? Nope, none. Sure, there are
> trouble-shooting tips, but what use are trouble-shooting tips if you
> can't even get started?

The information you're lacking seems not to be how to use QEMU, but 
rather how to install an OS on a bare ("virgin") system. This is not 
QUEM related. This was universal knowledge back in early PCs day (PC-XT, 
to be precise) ; the quasi-universal dissemination of preinstalled OSes 
(thanks to Microsoft's and Apple's grip on the market), made this 
knowledge unuseful for most of users, therefore more and more a nerd's 
knowledge.

In short : in order to install an OS on bare hardware, you have to boot 
this hardware on something coming in removable media, then use this 
installer to install the OS.

In olden days of yore, you booted on diskettes (or even on a tape (yuck 
!)), ad used the resulting running mini-OS to read another support 
(diskettes or tape(s) again) to install its content on the hardware hard 
disk. Nowadays, the boot medium and the OS distribution medium are 
merged in a common CDROM. So you boot an installer from  the (first) 
installation CDROM and use this installer to install the OS on the disk. 
Since booting and installing come from the same medium, the distinction 
became more and more blurred, thanks to the willingness of distribution 
creators more and more willing to "help" "unskilled" end-users. Hence 
the confusion...

With QEMU, the process is the same in principle, but slightly different 
in realization, due to the difference between real and simulated hardware.

You have to have an installation medium for your target OS, either 
physical (e. g. a cd-rom) or virttual (e. g. a cd-rom ISO image).
You start  by creating a *virgin* hard disk image (with qcow).
You then boot qemy by pointing it to your newly-created hard disk image 
as your first hard disk (e. g. -hda myharddisk.qcow), to your 
distribution medium or medium image as a cdrom (e. g. -cdrom /dev/cdrom, 
or -cdrom mymediumimage.iso), and telling qemu to boot on the 
distribution medium (image) with -boot d.

The installer boots on the emulated system and hand-helds you to install 
the target OS on what it thinks is the primary hard disk. At the end of 
installation, you will be prompted to reboot your system on 
yournewly-installed OS. At this stage, you should terminate QEMU and 
restarting it with the sames options as before, *except for the -boot 
option,*, which you change to "-boot c". This directs QEMU to boot on 
your newly-loaded hard disk.

> I've looked at qemu several times over the past several years. Every
> time I get excited at the prospect of migrating people to GNU/Linux by
> letting them run the one windows app they need...

For many cases (but not all, by a long way !), wine is a better solution 
to run a couple of "irreplacable" (??) Windows apps. Installing a full 
virtual machine and OS to run one app is a bit like using a sledgehammar 
to swat a fly...

>                                                    and every time I hit a
> brick wall, as qemu fails to actually do anything useful.
> 
> Try to take this approach: You are writing to a technically competent
> user (perhaps a sysadmin) who wants to run Windows under Linux with qemu
> (perhaps to migrate some of the company computers). He has a Windows
> install CD, he has qemu installed, and is ready to go. Please write
> something that this person can use to get Windows running under qemu.


I have to point out that any sysadmin worth his salt would have serious 
knowledge of system installation procedures, much more than what I've 
sketched above. This is ultrabasic knowledge to a sysadmin...

					Emmanuel Charpentier
				Remembering way more CP/M, TRSDOS
				VMS, MS-DOS, Unix, Windows and Linux
				installations than he wishes to
				acknowledge... Shit, I even remember
				how to boot a Mini-6 (a nice Bull mini
				from the 70's) !